Total Hardness

This method, called a complexometric titration, is used to find the total calcium and magnesium content in water and various solid materials. It can also be used to determine the total hardness of fresh water provided the solutions used are diluted.

The combined concentration of calcium and magnesium ions is considered to be the measure of water hardness.
The method uses a very large molecule called EDTA which forms a complex with calcium and magnesium ions. EDTA is short for ethylenediaminetetraacetic acid. A blue dye called Eriochrome Black T (ErioT) is used as the indicator. This blue dye also forms a complex with the calcium and magnesium ions, changing colour from blue to pink in the process. The dye–metal ion complex is less stable than the EDTA–metal ion complex. For the titration, the sample solution containing the calcium and magnesium ions is reacted with an excess of EDTA. The indicator is added and remains blue as all the Ca2+ and Mg2+ ions present are complexed with the EDTA.
A back titration is carried out using a solution of magnesium chloride. This forms a complex with the excess EDTA molecules until the end-point, when all the excess EDTA has been complexed. The remaining magnesium ions of the magnesium chloride solution then start to complex with ErioT indicator, immediately changing its colour from blue to pink.
The main reaction is:
Ca2+ + EDTA4- --> [Ca-EDTA]2-−
Back titration:
EDTA4- + Mg2+ --> [Mg-EDTA]2-− −
Indicator reaction: Note: ErioT is blue and ErioT-Mg is pink
ErioT + Mg2+ --> ErioT-Mg

Calcium Hardness

The Method is applicable to determine the calcium ion content in water samples aswell as the solid samples.

The Disodium salts of ethylene diamine tetra acetic acid ( Na2 EDTA) form slighly ionised colourless, stable complex with calcium ions. Muroxide is dark purple in the absence of calcium but with calcium form alight salamen coloured complex which has inonisation constant higher than Na2 EDTA complex. Hence by using muroxide indicator a solution containg ions may be titrated with Na2EDTA. the optimum pH = 10

Muroxide (NH4C8H4N5O6, or C8H5N5O6.NH3), also called ammonium purpurate or MX, is the ammonium salt of purpuric acid.

Muroxide in its dry state has the appearance of a reddish purple powder, slightly soluble in water. In solution, its color ranges from yellow in strong acidic pH through reddish-purple in weakly acidic solutions to blue-purple in alkaline solutions. The pH for titration of calcium is 11.3.

Molarity of EDTA solution is 0.01 M ; mL of 0.01 M EDTA = 1 mg of CaCO3
EDTA molarity x EDTA volume (L) = Ca+2 molarity x Ca+2 volume (L)

Chloride by Gravimetric Method

In Gravimetric method determines the chloride ion concentration of a solution by gravimetric analysis. A precipitate of silver chloride is formed by adding a solution of silver nitrate to the aqueous solution of chloride ions. The precipitate is collected by careful filtration and weighed.

Ag+(aq) + Cl-(aq) --> AgCl(s)

The precipitate can be collected more easily if the reaction solution is heated before filtering. This causes the solid silver chloride particles to coagulate. The precipitation is carried out under acidic conditions to avoid possible errors due to the presence of carbonate and phosphate ions which, under basic conditions, would also precipitate with the silver ions.

As the method requires very careful weighing of the samples, it is best to use it on solutions that are known to contain a fairly significant concentration of chloride ions, such as seawater. For this reason it should not be used for stream or river water.

Chloride by Volhard's Method

Volhard's method uses a back titration with potassium thiocyanate to determine the concentration of chloride ions in a solution. Before the titration an excess volume of a silver nitrate solution is added to the solution containing chloride ions, forming a precipitate of silver chloride.

The term ‘excess‘ is used as the moles of silver nitrate added are known to exceed the moles of sodium chloride present in the sample so that all the chloride ions present will react.

Ag+(aq) + Cl-(aq) --> AgCl(s)

The indicator Fe3+ (ferric ion) is then added and the solution is titrated with the potassium thiocyanate solution. The titrate remains pale yellow as the excess (unreacted) silver ions react with the thiocyanate ions to form a silver thiocyanate precipitate.

Ag+(aq) + SCN -(aq) --> AgSCN(s)

Once all the silver ions have reacted, the slightest excess of thiocyanate reacts with Fe3+ to form a dark red complex.

Fe3+(aq) + SCN -(aq) --> [FeSCN]2+(aq)

The concentration of chloride ions is determined by subtracting the titration findings of the moles of silver ions that reacted with the thiocyanate from the total moles of silver nitrate added to the solution. "This method is used when the pH of the solution after the sample has been prepared is acidic. If the pH is neutral or basic, Mohr’s method or the gravimetric method should be used".

Chloride by Mohr's Method

Mohr's method determines the chloride ion concentration of a solution by titration with silver nitrate. As the silver nitrate solution is slowly added, a precipitate of silver chloride forms.

Ag+(aq) + Cl-(aq) --> AgCl(s)

The indicator used is dilute potassium chromate solution. When all the chloride ions have reacted, any excess silver nitrate added will react with chromate ions to form a red-brown precipitate of silver chromate. This procedure is known as Mohr’s method.

2Ag+(aq) + CrO42-(aq) --> Ag2CrO4(s)

The procedure described here for seawater may also be applied to water samples from various other sources to determine the relative concentrations of chloride ions in, e.g., stream water, river water, estuary water.

Ryznar Stability Index (RSI)

Ryznar Stability Index (RSI)
The Ryznar stability index (RSI) uses a database of scale thickness measurements in municipal water systems to predict the effect of water chemistry.
Ryznar saturation index (RSI) was developed from empirical observations of corrosion rates and film formation in steel mains.

Ryznar saturation index is defined as:
RSI = 2 pHs – pH (measured)

RSI << 6 the scale tendency increases as the index decreases
RSI >> 7 the calcium carbonate formation probably does not lead to a protective corrosion inhibitor film·

RSI >> 8 mild steel corrosion becomes an increasing problem.

Langelier Saturation Index (LSI)

Langelier Saturation Index (LSI)
The Langelier Saturation Index (sometimes Langelier Stability Index) is a calculated number used to predict the calcium carbonate stability of water. It indicates whether the water will precipitate, dissolve, or be in equilibrium with calcium carbonate. Langelier developed a method for predicting the pH at which water is saturated in calcium carbonate (called pHs). The LSI is expressed as the difference between the actual system pH and the saturation pH.

Langelier saturation index is defined as:
LSI = pH (measured) – pHs

pH is the measured water pH
pHs is the pH at saturation in calcite or calcium carbonate and is defined as:
pHs = (9.3 + A + B) - (C + D)
A = (Log10 [TDS] - 1) / 10
B = -13.12 x Log10 (oC + 273) + 34.55
C = Log10 [Ca2+ as CaCO3] - 0.4
D = Log10 [alkalinity as CaCO3]

If the actual pH of the water is below the calculated saturation pH, the LSI is negative and the water has a very limited scaling potential. If the actual pH exceeds pHs, the LSI is positive, and being supersaturated with CaCO3, the water has a tendency to form scale. At increasing positive index values, the scaling potential increases.

LSI > 0, water is super saturated and tends to precipitate a scale layer of CaCO3
LSI = 0, water is saturated (in equilibrium) with CaCO3 . A scale layer of CaCO3 is neither precipitated nor dissolved
LSI < 0, water is under saturated and tends to dissolve solid CaCO3

In practice, water with an LSI between -0.5 and +0.5 will not display enhanced mineral dissolving or scale forming properties. Water with an LSI below -0.5 tends to exhibit noticeably increased dissolving abilities while water with an LSI above +0.5 tends to exhibit noticeably increased scale forming properties.
It is also worth noting that the LSI is temperature sensitive. The LSI becomes more positive as the water temperature increases. This has particular implications in situations where well water is used. The temperature of the water when it first exits the well is often significantly lower than the temperature inside the building served by the well or at the laboratory where the LSI measurement is made.

Hardness

Hard water is the type of water that has high mineral content (in contrast with soft water). Hard water minerals primarily consist of calcium (Ca2+), and magnesium (Mg2+) metal cations, and sometimes other dissolved compounds such as bicarbonates and sulfates. Calcium usually enters the water as either calcium carbonate (CaCO3), in the form of limestone and chalk, or calcium sulfate (CaSO4), in the form of other mineral deposits. The predominant source of magnesium is dolomite (CaMg(CO3)2).
More exact measurements of hardness can be obtained through a wet titration. The total water 'hardness' (including both Ca2+ and Mg2+ ions) is read as parts per million (ppm) or weight/volume (mg/L) of calcium carbonate (CaCO3) in the water. Although water hardness usually only measures the total concentrations of calcium and magnesium (the two most prevalent, divalent metal ions), iron, aluminium, and manganese may also be present at elevated levels in some geographical locations.
Classification of Water by Hardness Content

Concentration mg/L CaCO3 Description
0 - 75 soft
75 - 150 moderately hard
150 - 300 Hard
300 and up Very hard

Temporary hardness
Temporary hardness is caused by a combination of calcium ions and bicarbonate ions in the water. It can be removed by boiling the water or by the addition of lime (calcium hydroxide). Boiling promotes the formation of carbonate from the bicarbonate and precipitates calcium carbonate out of solution, leaving water that is softer upon cooling.
The following is the equilibrium reaction when calcium carbonate (CaCO3) is dissolved in water:
CaCO3(s) + H2CO3(aq) ⇋ Ca2+(aq) + 2HCO3-(aq)

Permanent hardness
Permanent hardness is hardness (mineral content) that cannot be removed by boiling. It is usually caused by the presence of calcium and magnesium sulfates and/or chlorides in the water, which become more soluble as the temperature rises. Despite the name, permanent hardness can be removed using a water softener or ion exchange column, where the calcium and magnesium ions are exchanged with the sodium ions in the column.

Measurement:
The method is based on the reaction of heavy metal ions and alkaline earth metal ions (mostly Ca and Mg) with EDTA in basic solution. The sample is titrated with EDTA solution of known concentration until the initially obtained violet colour of the solution has turned to stabile blue colour. Eriochrome black -T serves as an indicator with this measurement.

Different methods of endpoint (Titration)

Different Type of Endpoints:

pH indicator: This is a substance that changes colour in response to a chemical change. An acid-base indicator (e.g., phenolphthalein) changes colour depending on the pH.

Redox indicators are also frequently used. A drop of indicator solution is added to the titration at the start; when the colour changes the endpoint has been reached.
A potentiometer: can also be used. This is an instrument that measures the electrode potential of the solution. These are used for titrations based on a redox reaction; the potential of the working electrode will suddenly change as the endpoint is reached.
pH meter: This is a potentiometer that uses an electrode whose potential depends on the amount of H+ ion present in the solution. (This is an example of an ion-selective electrode.) This allows the pH of the solution to be measured throughout the titration. At the endpoint, there will be a sudden change in the measured pH. It can be more accurate than the indicator method, and is very easily automated.
Conductance: The conductivity of a solution depends on the ions that are present in it. During many titrations, the conductivity changes significantly. (For instance, during an acid-base titration, the H+ and OH- ions react to form neutral H2O. This changes the conductivity of the solution.) The total conductance of the solution depends also on the other ions present in the solution (such as counter ions). Not all ions contribute equally to the conductivity; this also depends on the mobility of each ion and on the total concentration of ions (ionic strength). Thus, predicting the change in conductivity is harder than measuring it.
Colour change: In some reactions, the solution changes colour without any added indicator. This is often seen in redox titrations, for instance, when the different oxidation states of the product and reactant produce different colours.
Precipitation: If the reaction forms a solid, then a precipitate will form during the titration. A classic example is the reaction between Ag+ and Cl- to form the very insoluble salt AgCl. This usually makes it difficult to determine the endpoint precisely. As a result, precipitation titrations often have to be done as "back" titrations.
An isothermal titration calorimeter: uses the heat produced or consumed by the reaction to determine the endpoint. This is important in biochemical titrations, such as the determination of how substrates bind to enzymes.
Thermometric titrimetry is an extraordinarily versatile technique. This is differentiated from calorimetric titrimetry by the fact that the heat of the reaction (as indicated by temperature rise or fall) is not used to determine the amount of analyte in the sample solution. Instead, the endpoint is determined by the rate of temperature change.
Spectroscopy can be used to measure the absorption of light by the solution during the titration, if the spectrum of the reactant, titrant or product is known. The relative amounts of the product and reactant can be used to determine the endpoint.

Amperometry can be used as a detection technique (amperometric titration). The current due to the oxidation or reduction of either the reactants or products at a working electrode will depend on the concentration of that species in solution. The endpoint can be detected as a change in the current. This method is most useful when the excess titrant can be reduced, as in the titration of halides with Ag+. (This is handy also in that it ignores precipitates.)

Back Titration: The term back titration is used when a titration is done "backwards": instead of titrating the original analyte, one adds a known excess of a standard reagent to the solution, then titrates the excess. A back titration is useful if the endpoint of the reverse titration is easier to identify than the endpoint of the normal titration. They are also useful if the reaction between the analyte and the titrant is very slow.

Titration Classification

Titrations can be classified by the type of reaction.

Different types of titration reaction include:
Acid-base titrations are based on the neutralization reaction between the analyte and an acidic or basic titrant. These most commonly use a pH indicator, a pH meter, or a conductance meter to determine the endpoint.
Redox titrations are based on an oxidation-reduction reaction between the analyte and titrant. These most commonly use a potentiometer or a redox indicator to determine the endpoint. Frequently either the reactants or the titrant have a colour intense enough that an additional indicator is not needed.
Complexometric titrations are based on the formation of a complex between the analyte and the titrant. The chelating agent EDTA is very commonly used to titrate metal ions in solution. These titrations generally require specialized indicators that form weaker complexes with the analyte. A common example is Eriochrome Black T for the titration of calcium and magnesium ions.

Zeta potential titration characterizes heterogeneous systems, such as colloids. Zeta potential plays role of indicator. One of the purposes is determination of iso-electric point when surface charge becomes 0. This can be achieved by changing pH or adding surfactant. Another purpose is determination of the optimum dose of the chemical for flocculation or stabilization.

Titration

Titration is a common laboratory method of quantitative chemical analysis that is used to determine the unknown concentration of a known reactant. Because volume measurements play a key role in titration, it is also known as volumetric analysis.

A reagent, called the titrant or titrator, of known concentration (a standard solution) and volume is used to react with a solution of the analyte or titrant whose concentration is not known.

Using a calibrated burette to add the titrant, it is possible to determine the exact amount that has been consumed when the endpoint is reached.

The endpoint is the point at which the titration is complete, as determined by an indicator.

This is ideally the same volume as the equivalence point - the volume of added titrant at which the number of moles of titrant is equal to the number of moles of analyte, or some multiple thereof (as in polyprotic acids).

In the classic strong acid-strong base titration, the endpoint of a titration is the point at which the pH of the reactant is just about equal to 7, and often when the solution permanently changes color due to an indicator. There are however many different types of titrations.

Turbidity

Turbidity is a principal physical characteristic of water and is an expression of the optical property that causes light to be scattered and absorbed by particles and molecules rather than transmitted in straight lines through a water sample.

It is caused by suspended matter or impurities that interfere with the clarity of the water. These impurities may include clay, silt, finely divided inorganic and organic matter, soluble colored organic compounds, and plankton and other microscopic organisms.

Jackson Candle Turbidimeter: (Year - 1900)
A water sample is poured into the tube until the visual image of the candle flame, as viewed from the top of the tube, is diffused to a uniform glow. When the intensity of the scattered light equals that of the transmitted light, the image disappears; the depth of the sample in the tube is read against the ppm-silica scale, and turbidity was measured in Jackson turbidity units (JTU).

Formazin Turbidity Units (FTU): (Year - 1926)

Formazin is a suitable suspension for turbidity standards when prepared accurately by weighing and dissolving 5.00 grams of hydrazine sulfate and 50.0 grams of hexamethylenetetramine in one liter of distilled water. The solution develops a white hue after standing at 25EC for 48 hours. A new unit of turbidity measurement was adopted called formazin turbidity units (FTU).

Nephelometric Turbidimeter (Year - 1970)

It determines turbidity by the light scattered at an angle of 90 Degree from the incident beam. A 90 Degree detection angle is considered to be the least sensitive to variations in particle size.
Nephelometry has been adopted by Standard Methods as the preferred means for measuring turbidity because of the method's sensitivity, precision, and applicability over a wide range of particle size and concentration. The nephelometric method is calibrated using suspensions of formazin polymer such that a value of 40 nephelometric units (NTU) is approximately equal to 40 JTU. The expression of turbidity is NTU.

Conductivity

Electrical Conductivity is the ability of a solution to transfer (conduct) electric current.

It is the reciprocal of electrical resistivity (ohms). Therefore conductivity is used to measure the concentration of dissolved solids which have been ionized in a polar solution such as water.

The unit of measurement commonly used is one millionth of a Siemen per centimeter (micro-Siemens per centimeter or µS/cm).

When measuring more concentrated solutions, the units are expressed as milli-Siemens/cm (mS/cm) i.e.- 10-3 S-cm (thousandths of a Siemen).

For ease of expression, 1000 µS/cm are equal to 1 mS/cm. Often times conductivity is simply expressed as either micro or milli Siemens.

However this unit of measurement is sometimes (incorrectly) referred to as micro-mho's rather than micro-Siemens. The expression "mho" was simply the word ohm spelled backwards. Conductivity measurement unit of expression into whole numbers.

TDS is really a gravimetric measurement, because in solution the solids are predominately present in ionic form, they can be approximated with conductivity.

The TDS scale uses 2 µS/cm = 1 ppm (part per million as CaCO3). It is also expressed as 1 mg/l TDS.

Temperature plays a major role in conductivity. Because ionic activity increases with increasing temperature, conductivity measurements are referenced to 25ºC. The coefficient used to correct for changes in temperature, β is expressed as a percentage per degree Celsius. For most applications, beta has a value of two. In order to establish the true value of beta a solution is measured at the elevated temperature (without temperature compensation). Then the solution is cooled and re-measured. β can then be exactly calculated for that particular solution.

pH

pH is a measure of the acidity or basicity of a solution.

• It is defined as the cologarithm of the activity of dissolved hydrogen ions (H+).
• Hydrogen ion activity coefficients cannot be measured experimentally, so they are based on theoretical calculations.
• The pH scale is not an absolute scale; it is relative to a set of standard solutions whose pH is established by international agreement.

The concept of pH was first introduced by Danish chemist Soren Peder Lauritz Sorensen at the Carlsberg Laboratory in 1909.

It is unknown what the exact definition of p stands for. Some references suggest the p stands for “Power”, others refer to the German word “Potenz” (meaning power in German), and still others refer to “potential”.

Jens Norby published a paper in 2000 arguing that p is a constant and stands for “negative logarithm”; which has also been used in other works.

H stands for Hydrogen. Sorensen suggested the notation "PH" for convenience, standing for "power of hydrogen", using the cologarithm of the concentration of hydrogen ions in solution, p[H] Although this definition has been superseded p[H] can be measured if an electrode is calibrated with solution of known hydrogen ion concentration.

Pure water is said to be neutral. The pH for pure water at 25 °C (77 °F) is close to 7.0. Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are said to be basic or alkaline.

Emission norms in India

1991 - Idle CO Limits for Gasoline Vehicles and Free Acceleration Smoke for Diesel Vehicles, Mass Emission Norms for Gasoline Vehicles.
1992 - Mass Emission Norms for Diesel Vehicles.
1996 - Revision of Mass Emission Norms for Gasoline and Diesel Vehicles, mandatory fitment of Catalytic Converter for Cars in Metros on Unleaded Gasoline.
1998 - Cold Start Norms Introduced.
2000 - India 2000 (Eq. to Euro I) Norms, Modified IDC (Indian Driving Cycle), Bharat Stage II Norms for Delhi.
2001 - Bharat Stage II (Eq. to Euro II) Norms for All Metros, Emission Norms for CNG & LPG Vehicles.
2003 - Bharat Stage II (Eq. to Euro II) Norms for 11 major cities.
2005 - From 1st April Bharat Stage III (Eq. to Euro III) Norms for 11 major cities.

2010 - Bharat Stage III Emission Norms for 4-wheelers for entire country whereas Bharat Stage - IV (Eq. to Euro IV) for 11 major cities

Difference Between Cracking and Reforming

Cracking:
Cracking is the process whereby complex molecules are broken down into simpler molecules :

Example : C36H74 + H2 ------> C2H6 + C34H70

Reforming:
Reforming is a process used to convert molecules having low octane ratings into hight- octane liquid products.

Example: CH3(CH2)6CH3 -----> CH3C(CH3)2CH2CH(CH3)CH3

Introduction to Spectroscopy

What Is Spectroscopy?

Spectroscopy is a technique that uses the interaction of energy with a sample to perform an analysis.
What Is a Spectrum?

The data that is obtained from spectroscopy is called a spectrum. A spectrum is a plot of the intensity of energy detected versus the wavelength (or mass or momentum or frequency, etc.) of the energy.
What Information Is Obtained?

A spectrum can be used to obtain information about atomic and molecular energy levels, molecular geometries, chemical bonds, interactions of molecules, and related processes. Often, spectra are used to identify the components of a sample (qualitative analysis). Spectra may also be used to measure the amount of material in a sample (quantitative analysis).
What Instruments Are Needed?

There are several instruments that are used to perform a spectroscopic analysis. In simplest terms, spectroscopy requires an energy source (commonly a laser, but this could be an ion source or radiation source) and a device for measuring the change in the energy source after it has interacted with the sample (often a spectrophotometer or interferometer).
What Are Some Types of Spectroscopy?

There are as many different types of spectroscopy as there are energy sources! Here are some examples:
Astronomical Spectroscopy Energy from celestial objects is used to analyze their chemical composition, density, pressure, temperature, magnetic fields, velocity, and other characteristics. There are many energy types (spectroscopies) that may be used in astronomical spectroscopy.
Atomic Absorption Spectroscopy Energy absorbed by the sample is used to assess its characteristics. Sometimes absorbed energy causes light to be released from the sample, which may be measured by a technique such as fluorescence spectroscopy.
Attenuated Total Reflectance Spectroscopy This is the study of substances in thin films or on surfaces. The sample is penetrated by an energy beam one or more times and the reflected energy is analyzed. Attenuated total reflectance spectroscopy and the related technique called frustrated multiple internal reflection spectroscopy are used to analyze coatings and opaque liquids.
Electron Paramagnetic Spectroscopy This is a microwave technique based on splitting electronic energy fields in a magnetic field. It is used to determine structures of samples containing unpaired electrons.
Electron Spectroscopy There are several types of electron spectroscopy, all associated with measuring changes in electronic energy levels.
Fourier Transform Spectrosopy This is a family of spectroscopic techniques in which the sample is irradiated by all relevant wavelengths simultaneously for a short period of time. The absorption spectrum is obtained by applying a mathematical analysis to the resulting energy pattern.
Gamma-ray Spectroscopy Gamma radiation is the energy source in this type of spectroscopy, which includes activation analysis and Mossbauer spectroscopy.
Infrared Spectroscopy The infrared absorption spectrum of a substance is sometimes called its molecular fingerprint. Although frequently used to identify materials, infrared spectroscopy also may be used to quantify the number of absorbing molecules.
Laser Spectroscopy Absorption spectroscopy, fluorescence spectroscopy, Raman spectroscopy, and surface-enhanced Raman spectroscopy commonly use laser light as an energy source. Laser spectroscopies provide information about the interaction of coherent light with matter. Laser spectrocopy generally has high resolution and sensitivity.
Mass Spectrometry A mass spectrometer source produces ions. Information about a sample may be obtained by analyzing the dispersion of ions when they interact with the sample, generally using the mass-to-charge ratio.
Multiplex or Frequency-Modulated Spectroscopy In this type of spectroscopy, each optical wavelength that is recorded is encoded with an audio frequency containing the original wavelength information. A wavelength analyzer can then reconstruct the original spectrum.
Raman Spectroscopy Raman scattering of light by molecules may be used to provide information on a sample's chemical composition and molecular structure.
X-ray Spectroscopy This technique involves excitation of inner electrons of atoms, which may be seen as x-ray absorption. An x-ray fluorescence emission spectrum may be produced when an electron falls from a higher energy state into the vacancy created by the absorbed energy.

Basic Concentration

The concentration of a chemical solution refers to the amount of solute that is dissolved in a solvent. We normally think of a solute as a solid that is added to a solvent (e.g., adding table salt to water), but the solute could just as easily exist in another phase. For example, if we add a small amount of ethanol to water, then the ethanol is the solute and the water is the solvent. If we add a smaller amount of water to a larger amount of ethanol, then the water could be the solute!

Units of Concentration
Once you have identified the solute and solvent in a solution, you are ready to determine its concentration. Concentration may be expressed several different ways, using percent composition by mass, mole fraction, molarity, molality, or normality.

1. Percent Composition by Mass (%)
This is the mass of the solute divided by the mass of the solution (mass of solute plus mass of solvent), multiplied by 100.

Example: Determine the percent composition by mass of a 100 g salt solution which contains 20 g salt.
Solution: 20 g NaCl / 100 g solution x 100 = 20% NaCl solution

2. Mole Fraction (X)
This is the number of moles of a compound divided by the total number of moles of all chemical species in the solution. Keep in mind, the sum of all mole fractions in a solution always equals 1.

Example: What are the mole fractions of the components of the solution formed when 92 g glycerol is mixed with 90 g water? (Molecular weight water = 18; molecular weight of glycerol = 92)
Solution: 90 g water = 90 g x 1 mol / 18 g = 5 mol water92 g glycerol = 92 g x 1 mol / 92 g = 1 mol glyceroltotal mol = 5 + 1 = 6 molx water = 5 mol / 6 mol = 0.833x glycerol = 1 mol / 6 mol = 0.167It's a good idea to check your math by making sure the mole fractions add up to 1:x water + x glycerol = .833 + 0.167 = 1.000

3. Molarity (M)
Molarity is probably the most commonly used unit of concentration. It is the number of moles of solute per liter of solution (not necessarily the same as the volume of solvent!).

Example: What is the Molarity of a solution made when water is added to 11 g CaCl2 to make 100 ml of solution?
Solution: 11 g CaCl2 / (110 g CaCl2 / mol CaCl2) = 0.10 mol CaCl2100 ml x 1 L / 1000 ml = 0.10 LMolarity = 0.10 mol / 0.10 LMolarity = 1.0 M

4. Molality (m)
Molality is the number of moles of solute per kilogram of solvent. Because the density of water at 25°C is about 1 kilogram per liter, molality is approximately equal to molarity for dilute aqueous solutions at this temperature. This is a useful approximation, but remember that it is only an approximation and doesn't apply when the solution is at a different temperature, isn't dilute, or uses a solvent other than water.

Example: What is the molality of a solution of 10 g NaOH in 500 g water?
Solution: 10 g NaOH / (4 g NaOH / 1 mol NaOH) = 0.25 mol NaOH500 g water x 1 kg / 1000 g = 0.50 kg watermolality = 0.25 mol / 0.50 kgmolality = 0.05 M / kgmolality = 0.50 m

5. Normality (N)
Normality is equal to the gram equivalent weight of a solute per liter of solution. A gram equivalent weight or equivalent is a measure of the reactive capacity of a given molecule. Normality is the only concentration unit that is reaction dependent.
Example: 1 M sulphuric acid (H2SO4) is 2 N for acid-base reactions because each mole of sulphuric acid provides 2 moles of H+ ions. On the other hand, 1 M sulphuric acid is 1 N for sulphate precipitation, since 1 mole of sulphuric acid provides 1 mole of sulphate ions.

Dilutions
You dilute a solution whenever you add solvent to a solution. Adding solvent results in a solution of lower concentration. You can calculate the concentration of a solution following a dilution by applying this equation:
Mi Vi = Mf Vf
where M is molarity, V is volume, and the subscripts i and f refer to the initial and final values.
Example: How many millilitres of 5.5 M NaOH are needed to prepare 300 ml of 1.2 M NaOH?
Solution: 5.5 M x V1 = 1.2 M x 0.3 LV1 = 1.2 M x 0.3 L / 5.5 MV1 = 0.065 litreV1 = 65 ml
So, to prepare the 1.2 M NaOH solution, you pour 65 ml of 5.5 M NaOH into your container and add water to get 300 ml final volume.

Measure Dissolved Oxygen? Why

Scientists want data for…
• Determine the mixing of air and water at the water’s surface
• Determine what animals can live in the water

Dissolved Oxygen
• Oxygen accounts for one of every five molecules in the air; on the other hand, in water, roughly five of every million molecules are dissolved oxygen, mg/L (ppm by mass)
• Test will measure the amount of free oxygen “gas” dissolved in your water sample in mg/L (ppm)
• Dissolved oxygen levels of at least 5 - 6 ppm (mg/L) are usually required for growth.
• Dissolved oxygen levels of below 3 ppm are stressful to most aquatic organisms.

The amount of oxygen that water can hold decreases with:
• Temperature increases
• Elevation increases (due to decreasing atmospheric pressure)
• Increasing amounts of dissolved substances (e.g., salts)

Biological Influences and Dissolved Oxygen

• As photosynthesis increases, oxygen levels increase:
Heat
CO2 + H2O ------> Biomass + O2

• As respiration increases due to decay or organic materials, oxygen levels decrease:

Biomass + O2 -----> CO2 + H2O

Sample collection and analysis:

• Rinse sampling bottle 3 times with sample water
• Submerge bottle in water and allow to fill.
• Tap bottle to release air bubbles
• While bottle is submerged, replace cap (If there are air bubbles in the bottle, empty and repeat)
• Preserve sample immediately. Test within 2 hours.
• Repeat 3 times. Take the average to see if all values are within the precision of the kit. Discard outliers.

Sample Preservation and Sample Testing
Dissolved Oxygen test kits involve two overall parts: sample preservation and sample testing.
• Preservation:
– 1st - addition of a chemical that precipitates in the presence of dissolved oxygen
– 2nd - addition of a chemical that causes the solids to dissolve and produce a colored solution. This should be done in the field.
• Sample Testing:
– Titration of preserved sample. This can be done in the lab.

Most DO test kits are based on the Winkler titration method

Chemical Reactions
To Preserve DO: Done in the field
O2 + 2 Mn2+ + 2H2O ----> 2Mn(IV)O2 + 4H+ (pH >10)
Allow precipitate to settle (reaction goes to completion)

2Mn(IV)O2 + 4H+ + 2I- ----> Mn2+ + I2 (yellow) + 2H2O (low pH)
DO is preserved

To Test Sample: This step can be done in the lab.
Na2S2O3 + 4I2 + 5H2O ----> 8I- + 2SO42- + 10H+ + Na+ (the titration)
Starch + I2 blue (to improve endpoint determination)

Quality Control
Check technique and quality of kit chemicals every 6 months.
– Rinse the 250 ml bottle twice with distilled water.
– Measure 100 ml of distilled water with a graduated cylinder and pour this water into the 250 ml bottle.
– Put the lid on tightly and shake vigorously for 5 minutes. The water will be saturated with dissolved oxygen.
– Uncap the bottle and take the temperature of the water. Be sure the tip of the thermometer does not touch the bottom or sides of the bottle. Record the temperature on the Hydrology Investigation Quality Control Procedure Data Sheet.
– To determine the dissolved oxygen value use a dissolved oxygen test kit that meets the specifications in the Toolkit of the GLOBE Teacher's Guide. Follow the instructions carefully.
– On the Hydrology Investigation Quality Control Procedure Data Sheet, record the value as mg/L DO for the saturated distilled water.
– The DO of the shaken distilled water must be within 1.0 mg/L of the expected value for a distilled water sample saturated with oxygen

To find the expected DO value for a saturated distilled water sample:
• Step 1: Using Table HYD-P-1 find the solubility of oxygen (mg/L) that corresponds to the temperature of your sample. Example: A temperature of 22 C has a corresponding DO solubility of 8.7 mg/L.
• Step 2: Using Table HYD-P-2 find the value that corresponds to your elevation. Example: An altitude of 1,544 meters has a corresponding saturation calibration value of 0.83.
• Step 3: Multiply the solubility of oxygen found in Step 1 by the calibration value found in Step 2. Example: At an altitude of 1,544 meters and a temperature of 22 C, 8.7 mg/L X 0.83 = 7.25 mg/L.
• Step 4: Compare this value to the DO value of the shaken distilled water.

Cetane Number

Cetane number or CN is a measurement of the combustion quality of diesel fuel during compression ignition. It is a significant expression of diesel fuel quality among a number of other measurements that determine overall diesel fuel quality. Cetane number of a fuel is defined as the percentage by volume of normal cetane in a mixture of normal cetane and alpha-methyl naphthalene which has the same ignition characteristics (ignition delay) as the test fuel when combustion is carried out in a standard engine under specified operating conditions..
Cetane number is actually a measure of a fuel's ignition delay; the time period between the start of injection and start of combustion (ignition) of the fuel. In a particular diesel engine, higher cetane fuels will have shorter ignition delay periods than lower cetane fuels. Cetane numbers are only used for the relatively light distillate diesel oils. For heavy (residual) fuel oil two other scales are used CCAI (Calculated Carbon Aromatic Index)and CII (Calculated Ignition index).
Generally, diesel engines run well with a CN from 40 to 55. Fuels with higher cetane number which have shorter ignition delays provide more time for the fuel combustion process to be completed. Hence, higher speed diesels operate more effectively with higher cetane number fuels. There is no performance or emission advantage when the CN is raised past approximately 55; after this point, the fuel's performance hits a plateau (A period in which progress stops for a while).

Alkyl nitrates (principally 2-ethyl hexyl nitrate) are used as additives to raise the cetane number called cetane improver.

Types of Density

Density or specific gravity of a liquid is meant its relative weight compared with the weight of an equal volume of pure water at a definite temperature. The determination of density is one of the most frequent operations in chemical work. This may be done with a pyknometer when very exact results are required, but in technical operations, sufficient accuracy for all practical purposes may be attained by the hydrometer. This is usually a glass instrument, consisting of a cylindrical bulb, weighted at the lower end, and drawn out at the upper end to a long, slender tube, carrying a scale. The gradations of the scale begin at the top and read downward, the numerically greater reading being at the bottom, except in one instance, - that of Baumé's scale for liquids lighter than water.Since the density of a liquid varies as its temperature changes, the scale is adjusted to a certain temperature, usually about 15 degrees C., at which determinations must be made. When the hydrometer is placed in a liquid, it sinks sufficiently to displace a volume of the liquid equal in weight to the weight of the instrument, and floats in an upright position. Should the hydrometer sink so deeply into the liquid that the scale is entirely below the surface, the density is less than the spindle is intended to measure, and one having lower * numerical readings should be used. If, on the contrary, the spindle does not sink deep enough to bring the scale into the liquid, an instrument having higher numerical scale readings is necessary.Three systems of hydrometer scales are in common use, besides a great number of special scales intended to give one particular factor in the density of a liquid; e.g. the per cent of alcohol in a mixture of alcohol and water, or the amount of sugar in a syrup, etc.

The direct specific gravity hydrometer is so constructed thatthe reading on its scale shows the density of the liquid directly as compared with pure water at the same temperature (15 degrees C.). Its scale is adapted to liquids heavier or lighter than water. The point to which it sinks in pure water at 15 degrees C. is marked 1.000. As usually furnished, a set of these hydrometers consists of four spindles, the scale being thus divided into four sections. The first spindle, with gradations from 0.700 to 1.000, is for liquids lighter than water, and the others are for those heavier than water. The scale is usually divided about as follows: 1.000 to 1.300 on the second spindle, 1.300 to 1.600 on the third, and 1.600 to 2.000 on the fourth. The gradations at the top of each spindle are further apart than those at the bottom of the stem,* rendering the reading somewhat more difficult in dense liquids than in those of lighter gravity.

Twaddell's hydrometer is also a direct reading instrument. The system consists of a series of spindles (usually six in number) carrying gradations from 0 to 174. The reading in pure water, at 15.5° C., is taken as 0, and each subsequent rise of 0.00;) sp. gr. is recorded on the scale as one additional division. Thus 10 Twaddell becomes 1.050 sp. gr. The gradations on this scale are also closer together as the density increases, but as its total length is divided among six spindles, the readings are not so difficult even at the highest densities. The instruments arc small, the gradations on each stem occupying about three lineal' inches, so that it may easily be used in an ordinary 100 cc. measuring cylinder. For the reasons that it is easy to read, requires but a small quantity of liquid to he tested, and permits a ready conversion of its readings into specific gravity by a very simple calculation, this is the most convenient hydrometer for ordinary factory or laboratory use. It is, however, not adapted to liquids lighter than water.Twaddell readings are converted into specific gravity as follows: Multiply the reading by .005, and add 1.000 to the product. Thus 15 Twaddell becomes 1.075 sp. gr. (1.000 +[15 X .005J = 1.075.)Baumé's hydrometer is a very unscientific instrument, but islargely used in technical. work. Its readings bear no very directrelation to true specific gravity. Baumé dissolved 15 parts of pure salt in 85 parts of pure water at 12.5° C. The point to which his instrument sank in this solution was marked 15; the point to which .it sank in pure water was marked O. The distance between these points was divided into fifteen equal parts, and the entire stem marked off in divisions of this width. This produced an instrument for liquids heavier than water.For liquids lighter than water, the point to which the instrument sank in a 10 per cent solution of salt was marked 0, and that to which it sank in distilled water was marked 10, the distance between these points was divided into 10 equal parts, and this gradation continued the entire length of the spindle. The 0 thus being placed at the bottom of the stem, the lighter the gravity of the liquid tested, the greater numerically is the reading of the scale. For instance, a liquid reading 70 Bé. is of less density than one of 50 Bé., which in turn is lighter than water at 10 Bé.

The pyknometer is not very often used in technical work, but a brief description of it may not be out of place here. It consists of a small bottle, having ground into its neck a capillary tube enlarged at its upper end, to form a reservoir which is closed by a stopper. The tube is removed and the bottle filled with the liquid to be tested; the tube is then inserted tightly, the liquid displaced rising through the capillary to the enlarged part of the tube. The stopper is then loosely inserted and the bottle placed in a bath at the temperature at which the density is to be taken. When the bottle and contents have reached this temperature the stopper is taken out and the liquid in the reservoir removed by means of absorbent paper, until the level of the liquid recedes within the capillary to a mark thereon. 'fhe stopper is then tightly inserted and the bottle removed from the bath, and after cleaning and drying its outside, allowed to stand until it reaches the normal temperature of the room. It is then weighed, and the density of the liquid is calculated from its known volume, previously determined by calibration of the bottle.

Westphal's balance is a special form of balance for determining the density of liquids. A glass plummet of known weight and volume is suspended from the beam by a fine platinum wire, and is submerged in the liquid to be tested. The weight which the plummet loses by this submersion is the weight of the volume ofliquid it displaces. The characteristic feature of the instrument is the decimal graduation of the beam, with the use of riders of 0.1, 0.01, and 0.001 part of the weight of the water displaced by the plummet. This permits the actual specific gravity to be at once read off on the beam, as soon as the latter has been brought to equilibrium with the plummet suspended in the liquid.

COD

In environmental chemistry, the chemical oxygen demand (COD) test is commonly used to indirectly measure the amount of organic compounds in water. Most applications of COD determine the amount of organic pollutants found in surface water (e.g. lakes and rivers), making COD a useful measure of water quality. It is expressed in milligrams per liter (mg/L), which indicates the mass of oxygen consumed per liter of solution. Older references may express the units as parts per million (ppm).

"The basis for the COD test is that nearly all organic compounds can be fully oxidized to carbon dioxide with a strong oxidizing agent under acidic conditions".

All organic matter to be completely oxidized, an excess amount of potassium dichromate (or any oxidizing agent) must be present. Once oxidation is complete, the amount of excess potassium dichromate must be measured to ensure that the amount of Cr3+ can be determined, by titration with ferrous ammonium sulphate (FAS) until the entire excess oxidizing agent has been reduced to Cr3+.

Typically, the oxidation-reduction indicator Ferroin is added during this titration step as well. Once all the excess dichromate has been reduced, the Ferroin indicator changes from blue-green to reddish-brown.

The amount of ferrous ammonium sulphate added is equivalent to the amount of excess potassium dichromate added to the original sample.

Interference:

Some samples of water contain high levels of oxidisable inorganic materials which may interfere with the determination of COD. Because of its high concentration in most wastewater, chloride is often the most serious source of interference. Its reaction with potassium dichromate follows the equation:

6Cl + Cr2O7 + 14 H ---> 3 Cl2 + 2 Cr + 7H2O

Prior to the addition of other reagents, mercuric sulphate can be added to the sample to eliminate chloride interference.

DO and BOD

DO
Oxygen is measured in its dissolved form as dissolved oxygen (DO).

DO is measured either in milligrams per liter (mg/L) or "percent saturation." Milligrams per liter is the amount of oxygen in a liter of water. Percent saturation is the amount of oxygen in a liter of water relative to the total amount of oxygen that the water can hold at that temperature.

A dissolved oxygen meter is an electronic device that converts signals from a probe that is placed in the water into units of DO in milligrams per liter. Most meters and probes also measure temperature. The probe is filled with a salt solution and has a selectively permeable membrane that allows DO to pass from the stream water into the salt solution. The DO that has diffused into the salt solution changes the electric potential of the salt solution and this change is sent by electric cable to the meter, which converts the signal to milligrams per liter on a scale

BOD

The amount of oxygen consumed by these organisms in breaking down the waste is known as the biochemical oxygen demand or BOD.

BOD also measures the chemical oxidation of inorganic matter (i.e., the extraction of oxygen from water via chemical reaction). A test is used to measure the amount of oxygen consumed by these organisms during a specified period of time (usually 5 days at 20 C). The rate of oxygen consumption in a stream is affected by a number of variables: temperature, pH, the presence of certain kinds of microorganisms, and the type of organic and inorganic material in the water.

BOD directly affects the amount of dissolved oxygen in rivers and streams. The greater the BOD, the more rapidly oxygen is depleted in the stream. This means less oxygen is available to higher forms of aquatic life. The consequences of high BOD are the same as those for low dissolved oxygen: aquatic organisms become stressed, suffocate, and die.

BOD measurement requires taking two samples at each site. One is tested immediately for dissolved oxygen, and the second is incubated in the dark at 20 C for 5 days and then tested for the amount of dissolved oxygen remaining.

The difference in oxygen levels between the first test and the second test, in milligrams per liter (mg/L), is the amount of BOD.

This represents the amount of oxygen consumed by microorganisms to break down the organic matter present in the sample bottle during the incubation period. Because of the 5-day incubation, the tests should be conducted in a laboratory.

Sometimes by the end of the 5-day incubation period the dissolved oxygen level is zero. This is especially true for rivers and streams with a lot of organic pollution. Since it is not known when the zero point was reached, it is not possible to tell what the BOD level is.

In this case it is necessary to dilute the original sample by a factor that results in a final dissolved oxygen level of at least 2 mg/L. Special dilution water should be used for the dilutions. (See APHA, 1992.) It takes some experimentation to determine the appropriate dilution factor for a particular sampling site. The final result is the difference in dissolved oxygen between the first measurement and the second after multiplying the second result by the dilution factor.

The first bottle should be analyzed just prior to storing the second sample bottle in the dark for 5 days at 20 C. After this time, the second bottle is tested for dissolved oxygen using the same method that was used for the first bottle. The BOD is expressed in milligrams per liter of DO using the following equation:
DO (mg/L) of first bottle - DO (mg/L) of second bottle = BOD (mg/L)

Two Basic Types of Skills

Two Basic Types of Skills
1. Hard skills
2. Soft skills

Hard Skills
Hard skills are technical skills. Like writing programs for computers, preparing a balance sheet, working on a particular machine for a particular process in a manufacturing workshop, acting in a television serial or a cinema film, carrying out a surgery etc.
One must have proficiency in these skills in order to become a good professional in one's chosen fields and to earn decent living.
Hard skills are important and you should never undermine them. They are your bread and butter skills.
Hard skills are more rational types.

Soft Skills
One can do a still better job of one's chosen professions if one also acquires proficiency in those soft skills which are required to perform the jobs better. These soft skills are behavioural in nature. For example, how do you communicate with the people, how good are you in making business presentations, how empathetic you are with the people you come across, can you work as a team member, do you manage your time well and so on.
These skills make all the difference. Mere technical skills allow you certain degree of success. You can achieve higher degree of success if you equip yourself with soft skills too.
Technical skills are obvious and people learning them find it easy to understand and follow the processes of acquiring these skills.
However, one wonders as to what is there to learn in soft skills; you are already doing them. Say, communication. You have been speaking and listening from the very young age and so, one may think as to what is there to learn more and how to learn. But if you look around, you may find that some people are more effective in speaking than others. Here is the answer. The people who speak more effectively have learnt and practiced to speak effectively. They have followed and implemented certain processes and guidelines for speaking more effectively. It did hot happen to them accidentally or automatically.
Soft skills make a difference in the external and internal personalities. People who acquire soft skills of high order are more sophisticated, more cultured, more reformed and are found to be more successful in every walk of life.
Therefore, in addition to perfecting your hard skills, also try to perfect your soft skills.
Soft skills improve your emotional intelligence

Both Skills Necessary
For example, a tourist guide has to know the technical aspects of his job like showing his tourists the right places in a proper sequence with authentic commentary on them, the legalities of his job, the safety aspect of his tourists etc, yet, he will be more in demand and earn more if he also has the necessary soft skills for the job like manners and etiquette, interpersonal relations with tourists, humour, creativity etc.

Viscosity and Density

Viscosity and Density (Metric SI Units)
In the SI system of units the kilogram (kg) is the standard unit of mass, a cubic meter is the standard unit of volume and the second is the standard unit of time.

Density p
The density of a fluid is obtained by dividing the mass of the fluid by the volume of the fluid. Density is normally expressed as kg per cubic meter.
p = kg/m3
Water at a temperature of 20°C has a density of 998 kg/m3
Sometimes the term ‘Relative Density’ is used to describe the density of a fluid.
Relative density is the fluid density divide by 1000 kg/m3
Water at a temperature of 20°C has a Relative density of 0.998
Dynamic Viscosity µ

Viscosity describes a fluids resistance to flow.
Dynamic viscosity (sometimes referred to as Absolute viscosity) is obtained by dividing the Shear stress by the rate of shear strain.
The units of dynamic viscosity are: Force / area x time The Pascal unit (Pa) is used to describe pressure or stress = force per area. This unit can be combined with time (sec) to define dynamic viscosity.
µ = Pa•s
1.00 Pa•s = 10 Poise = 1000 Centipoise
Centipoise (cP) is commonly used to describe dynamic viscosity because water at a temperature of 20°C has a viscosity of 1.002 Centipoise.
This value must be converted back to 1.002 x 10-3 Pa•s for use in calculations.

Kinematic Viscosity v
Sometimes viscosity is measured by timing the flow of a known volume of fluid from a viscosity measuring cup. The timings can be used along with a formula to estimate the kinematic viscosity value of the fluid in Centistokes (cSt).
The motive force driving the fluid out of the cup is the head of fluid.
This fluid head is also part of the equation that makes up the volume of the fluid.
Rationalizing the equations the fluid head term is eliminated leaving the units of Kinematic viscosity as area / time v = m2/s
m2/s = 10000 Stokes = 1000000 Centistokes.
Water at a temperature of 20°C has a viscosity of 1.004 x 10-6 m2/s. This evaluates to 1.004000 Centistokes.
This value must be converted back to 1.004 x 10-6 m2/s for use in calculations.
The kinematic viscosity can also be determined by dividing the dynamic viscosity by the fluid density.

Kinematic Viscosity and Dynamic Viscosity Relationship
Kinematic Viscosity = Dynamic Viscosity / Density
v = µ / p
Centistokes = Centipoise / Density

To understand the metric units involved in this relationship it will be necessary to use an example:
Dynamic viscosity µ= Pa
Substitute for Pa = N/m2 and N = kg• m/s2
Therefore µ = Pa•s = kg/(m•s)
Density p = kg/m3
Kinematic Viscosity = v = µ /p = (kg/(m•s) x 10-3) / (kg/m3) = m2/s x 10-6

Viscosity and Density (Imperial Units)
In the Imperial system of units the pound (lb) is the standard unit of weight, a cubic foot is the standard unit of volume and the second is the standard unit of time.
The standard unit of mass is the slug.
This is the mass that will accelerate by 1 ft/s when a force of one pound (lbf) is applied to the mass. The acceleration due to gravity (g) is 32.174 ft per second per second.
To obtain the mass of a fluid the weight (lb) must be divided by 32.174.

Density p
Density is normally expressed as mass (slugs) per cubic foot.
The weight of a fluid can be expressed as pounds per cubic foot.
p = slugs/ft 3
Water at a temperature of 70°F has a density of 1.936 slugs/ft3 (62.286 lbs/ft3)

Dynamic Viscosity µ
The units of dynamic viscosity are: Force / area x time µ = lb•s/ft2
Water at a temperature of 70°F has a viscosity of 2.04 x 10-5 lb•s/ft2
1.0 lb•s/ft2 = 47880.26 Centipoise

Kinematic Viscosity v
The units of Kinematic viscosity are area / time v = ft2/s
1.00 ft 2/s = 929.034116 Stokes = 92903.4116 Centistokes
Water at a temperature of 70°F has a viscosity of 10.5900 x 10-6 ft2/s (0.98384713 Centistokes)

Kinematic Viscosity and Dynamic Viscosity Relationship
Kinematic Viscosity = Dynamic Viscosity / Density v = µ / p
The imperial units of kinematic viscosity are ft2/s
To understand the imperial units involved in this relationship it will be necessary to use an example:
Dynamic viscosity µ = lb•s/ft2
Density p = slugs/ft3
Substitute for slug = lb/32.174 ft•s2
Density p = (lb/32.174 ft•s2)/ft3= (lb/32.174•s2)/ft4
Note: slugs/ft3 can be expressed in terms of lb•s2/ft 4
Kinematic Viscosity v = (lb•s/ft2)/(slugs/ft3)
Substitute lb•s2/ft 4 for slugs/ft3
Kinematic Viscosity v = (lb•s/ft2 )/(lb•s2/ft4) = ft2/s

Types of Interview

1. Unstructured interview - Unstructured interview are a method of interviews where questions can be changed to meet the respondent’s intelligence, understanding.

2. Structured interview -The interviewer has a standard set / sequence of questions that are asked of all candidates.• Interviewers read the questions exactly as they appear on the survey questionnaire.

3. Screening interview - Screening interviews are generally conducted when an employer has a large applicants which they want to narrow down to a more manageable number.

4. Behavioural interview - In behavioural interviews, candidates are asked to explain their skills, experience, activities etc - as examples of your past behaviour.

5. Stress interview - The stress interview is designed to find applicants who can handle stress, and handle it well.

6. Situational interview - A situational interview utilizes hypothetical events in the form of a question. Candidates are asked how they would react if they encountered that event.

7. Phone interview - Phone interview is a method which is conducted by telephone.

8. One to one interview - Face to Face interview (one to one interview) is most common interview method and just involves interviewer and interviewee alone in a private office.

9. Group interview - All the candidates/job seekers will be in the same room during the interview.
10. Panel interview - A panel interview is a technique that allows several member of a hiring company to interview a interviewee at the same time.

What is XRF?

X-ray fluorescence (XRF) is the emission of characteristic "secondary" (or fluorescent) X-rays from a material that has been excited by bombarding with high-energy X-rays or gamma rays.

XRF is an analytical method for determining the chemical composition of all kinds of materials. The materials can be solid, liquid, power, filtered or then form. XRF can also somtimes be used to determine the thickness and composition of layers and coatings.

The method is fast, accurate and non-destructive and usually requires only a minimum of sample preparation. Applications are very broad and include the metal, cement, oil, plastic and food industries along with mining, mineralogy and geology and environmental analysis of water and waste materials. XRF is also a very useful analysis technique for research and pharmacy.

XRF - Spectrometer system can be divided into two main group:

1. Energy Dispersive System (EDXRF) and

2. Wavelength Dispersive System (WDXRF)

The elements that can be analysed and their detection level mainly depend on the spectrometer system used. The elemental range for EDXRF goes from Sodium to Uranium (Na to U). For WDXRF it is even wider, from Beryllium to Uranium (Be to U). The concentration range goes from sub -ppm level to 100%. Generally speaking the elements with high atomic numbers have better detection limits than lighter elements.

Precision and reproducibility of XRF analysis very high. very accurate results are possible when good standard specimans are available, but also in applications where no specific standard can be found.

The measurement time depends on the number of elements to be determined the required accuracy, and varies between seconds and 30 minutes. The analysis time after a measurements is only very few seconds.

Energy dispersive spectrometry
In energy dispersive spectrometers (EDX or EDS), the detector allows the determination of the energy of the photon when it is detected. Detectors historically have been based on silicon semiconductors, in the form of lithium-drifted silicon crystals, or high-purity silicon wafers.

Wavelength dispersive spectrometry
In wavelength dispersive spectrometers (WDX or WDS), the photons are separated by diffraction on a single crystal before being detected. Although wavelength dispersive spectrometers are occasionally used to scan a wide range of wavelengths, producing a spectrum plot as in EDS, they are usually set up to make measurements only at the wavelength of the emission lines of the elements of interest.

The characteristic radiation produced directly by the X-rays coming from the source is called "PRIMARY FLUORESCENCE" while that produced in the sample by primary fluorescence of other atoms is called "SECONDARY FLUORESCENCE"

Accuracy, Precision & Bias

This target has been struck with a high degree of precision, yet a low degree of accuracy.

This target has been hit with a high degree of accuracy, yet a low degree of precision.

Accuracy
Accuracy refers to the agreement between experimental data and a known value. You can think of it in terms of a bullseye in which the target is hit close to the center, yet the marks in the target aren't necessarily close to each other.

The "trueness" or the closeness of the analytical result to the "true" value. It is constituted by a combination of random and systematic errors (precision and bias) and cannot be quantified directly. The test result may be a mean of several values. An accurate determination produces a "true" quantitative value, i.e. it is precise and free of bias.

Precision

Precision refers to how well experimental values agree with each other. If you hit a bullseye precisely, then you are able to hit the same spot on the target each time, even though that spot may be distant from the center.

The closeness with which results of replicate analyses of a sample agree. It is a measure of dispersion or scattering around the mean value and usually expressed in terms of standard deviation, standard error or a range (difference between the highest and the lowest result).

Keep in Mind - Data can be very precise such that each data point is close to the others, yet contain a high degree of experimental error.

Bias
The consistent deviation of analytical results from the "true" value caused by systematic errors in a procedure. Bias is the opposite but most used measure for "trueness" which is the agreement of the mean of analytical results with the true value, i.e. excluding the contribution of randomness represented in precision. There are several components contributing to bias:

1. Method bias
The difference between the (mean) test result obtained from a number of laboratories using the same method and an accepted reference value. The method bias may depend on the analyte level.

2. Laboratory bias
The difference between the (mean) test result from a particular laboratory and the accepted reference value.

3. Sample bias
The difference between the mean of replicate test results of a sample and the ("true") value of the target population from which the sample was taken. In practice, for a laboratory this refers mainly to sample preparation, subsampling and weighing techniques. Whether a sample is representative for the population in the field is an extremely important aspect but usually falls outside the responsibility of the laboratory (in some cases laboratories have their own field sampling personnel).

Tips for Gas Cylinder Safety

Top 10 Tips for Safely Handling and Using Gas Cylinders Not every one needs to know that fluorine will violently ignite many substances, that silane burns on contact with air, or that ammonia will decompose thermally into twice its volume. But if you work with specialty gases, this information is essential. Safety must always be a primary goal when working with specialty gases? safety and knowledge go hand-in-hand. To improve your chances of preventing hazardous accidents, follow these Top 10 Tips for safely handling and using gas cylinders:

1. Appropriate firefighting, personnel safety and first aid equipment should always be available in case of emergencies. Ensure adequate personnel are trained in the use of this equipment.
2. Obtain a copy of the MSDS for the gases being used. Read the MSDS thoroughly and become familiar with the gas properties and hazards prior to use.
3. Follow all federal, state and local regulations concerning the storage of compressed gas cylinders. Store gas cylinders in a ventilated and well lit area away from combustible materials.
Separate gases by type and store in assigned locations that can be readily identified. Store cylinders containing flammable gases separately from oxygen cylinders and other oxidants by a fireresistant barrier (having a fire-resistance rating of at least 30 minutes) or locate them at least 20 feet apart from each other. Store poison, cryogenic and inert gases separately. If a cylinder's contents are not clearly identified by the proper cylinder markings labels, do NOT
accept for use.
4. Storage areas should be located away from sources of excess heat, open flame or ignition, and not located in closed or sub-surface areas. The area should be dry, cool and well ventilated. Outdoor storage should be above grade, dry and protected from the extremes of weather. While in storage, cylinder valve protection caps MUST be firmly in place.
5. Arrange the cylinder storage area so that old stock is used first. Empty cylinders should be stored separately and identified with clear markings. Return empty cylinders promptly. Some pressure should be left in a depleted cylinder to prevent air suck-back that would allow moisture and contaminants to enter the cylinder 6. Do not apply any heating device that will heat any part of a cylinder above 125°F (52°C). Overheating can cause the cylinder to rupture. Neither steel nor aluminum cylinder temperatures should be permitted to exceed 125°F (52°C).
7. Safety glasses, gloves and safety shoes should be worn at all times when handling cylinders. Always move cylinders by hand trucks or carts that are designed for this purpose. During transportation, keep both hands on the cylinder cart and secure cylinders properly to prevent them from falling, dropping or striking each other. Never use a cylinder cart without a chain or transport a gas cylinder without its valve protection cap firmly in place.
8. To begin service from a cylinder, first secure the cylinder and then remove the valve protection cap. Inspect the cylinder valve for damaged threads, dirt, oil or grease. Remove any dust or dirt with a clean cloth. If oil or grease is present on the valve of a cylinder which contains oxygen or another oxidant, do NOT attempt to use it. Such combustible substances in contact with an oxidant are explosive. Always disconnect equipment from the cylinder when not in use and return the cylinder valve protection cap to the cylinder.
9. Be sure all fittings and connection threads meet properly - never force. Dedicate your regulator to a single valve connection even if it is designed for different gases. NEVER cross thread or use adapters between non-mating equipment and cylinders. Use washers only if indicated. Never use pipe dope on pipe threads, turn the threads the wrong way, or use Teflon® tape on the valve threads to prevent leaking
10. When a cylinder is in use, it must be secured with some form of fastener. Floor or wall brackets are ideal for stationary use. Portable bench brackets are recommended for when a cylinder must be moved around. Smaller stands function well for lecture bottle use.

GC - FID response factor

Flame Ionization Detector response factors referred to methane or propane
Need not to find any book. Weigh accurately Methanol and propanol and note down the weight. run on GC . Find out the area % Now % wt / % area = Response factor

7 Qualities of a Good Leader

1. A good head to be able to evaluate the quality of ideas and Suggestions presented to him.
2. A good heart to be able to be compassionate and fair with the people.
3. A good spirit to be able to hear the voice of God. Some paths God will lead you down don't make head and heart sense at the Time.
4. A good eye to be able to see things other people cannot.
5. A good tongue to be able to communicate the vision to the People and motivate them to follow.
6. A good hand to be able to do the things that need to be Done. Knowing the right way is not the same as doing it.
7. A good foot to set an example for the people. A minor flaw Can outshine a major mission in the eyes of small minds.

PTB to PPM Conversion

1 pound = 453.592 gm
1 Barrel =158.987 lit
1 PTB =1 pound / 1000 barrel
=453.592 gm / 1000 * 158.987 lit
PPM = mg / Litre
=(453.592 *1000) mg / (1000* 158.987) lit
Therefore =(453.592 *1000) mg / (1000 *158.987)lit
=453592 mg / 158987 lit
1 PTB =2.8530 PPM
1 PPM =0.3505 PTB

14S of Self

1. Self - You, you only
2. Self-concept - Belief about yourself based on your own experiences
3. Self-awareness -Aware of oneself, including one's traits, feelings, and behaviours
4. Self-actualization - Realize all of one's potentialities
5. Self-confidence - Sense of self-worth and capabilities
6. Self-conscious - Paying attention to our self as a whole
7. Self-esteem - How we feel about or value ourself
8. Self-efficacy - Belief that one is capable of performing in a certain manner to attain certain goals.
9. Self-control - Able to manage one’s own disruptive thinking, feeling and impulsive action
10. Self-regulation - Guidance of one’s own goal directed thinking, feeling and action.
11. Self-monitoring - Our ability to monitor our self
12. Self-instruction - You talk /instruct to your self
13. Self-motivation - Working in a careful and consistent manner without giving up.
14. Self-transcendence - Going beyond or above the limitations of one's self.

Health - Personality Guide

Health:
1. Drink plenty of water.
2. Eat breakfast like a king, lunch like a prince and dinner like a beggar.
3. Eat more foods that grow on trees and plants and eat less food that is manufactured in plants.
4. Live with the 3 E's -- Energy, Enthusiasm, and Empathy.
5. Make time to practice meditation, yoga, and prayer.
6. Play more games.
7. Read more books than you did in 2008.
8. Sit in silence for at least 10 minutes each day.
9. Sleep for 7 hours.
10. Take a 10-30 minutes walk every day. And while you walk, smile.
Personality:
11. Don't compare your life to others'. You have no idea what their journey is all about.
12. Don't have negative thoughts or things you cannot control. Instead invest your energy in the positive present moment.
13. Don't over do. Keep your limits.
14. Don't take yourself so seriously. No one else does.
15. Don't waste your precious energy on gossip.
16. Dream more while you are awake.
17. Envy is a waste of time. You already have all you need.
18. Forget issues of the past. Don't remind your partner with his/her mistakes of the past. That will ruin your present happiness.
19. Life is too short to waste time hating anyone. Don't hate others.
20. Make peace with your past so it won't spoil the present.
21. No one is in charge of your happiness except you.
22. Realize that life is a school and you are here to learn. Problems are simply part of the curriculum that appear and fade away like algebra class but the lessons you learn will last a lifetime.
23. Smile and laugh more.
24. You don't have to win every argument. Agree to disagree.
Society:
25. Call your family often.
26. Each day give something good to others.
27. Forgive everyone for everything.
28. Spend time with people over the age of 70 & under the age of 6.
29. Try to make at least three people smile each day.
30. What other people think of you is none of your business.
31. Your job won't take care of you when you are sick. Your friends will. Stay in touch.
Life:
32. Do the right thing!
33. Get rid of anything that isn't useful, beautiful or joyful.
34. GOD heals everything.
35. However good or bad a situation is, it will change.
36. No matter how you feel, get up, dress up and show up.
37. The best is yet to come.
38. When you awake alive in the morning, thank GOD for it.
39. Your Inner most is always happy. So, be happy.
Last but not the least:
40. Please Forward this message to everyone you care about

Address proof card

Working people when shift their houses, it is difficult for them to produce an address proof issued by Government with the latest address.India post (post office) has come up with a solution.Now you can get an Address proof along with your photo from India post. The address proof issued by India post, which is a central government organization, is similar to Government ID cards like Driving license, Voters ID etc. It can be used for opening bank accounts, for getting telephone/internet connections etc.The total cost for getting this ID card is Rs.250/ (Rs.10 for application and Rs.240/- processing fee).Inform everybody. This is very useful For more details enquire in the nearest post office. For authentication, check http://www.indiapost.gov.in/Netscape/MailServices.html