ANALYTICALCHEMISTRY
Analytical Chemistryis the branch of chemistry concerned with determining the qualitative and quantitative composition of substances. It is a branch which is broad in scope and its applications extend to all parts of an industrialized society.
The two main sub-branches of Analytical Chemistry are:
- Qualitative analysis: The determination of the identity of chemical species present in a sample
and
- Quantitative analysis: An examination to determine how much of a particular species is present in a sample.
The procedure followed while doinga chemical analysis can be classified as either aclassical (“wet”) procedure or aninstrumentalprocedure. Therefore, both qualitative and quantitative analysis are sub-divided into classical (“wet”) analysis and instrumental analysis.
In wet procedures chemical reactions are used to perform the analysis and there is no use of any mechanical or electronic instrument except of an analytical balance. Main sub-branches of classical ("wet") analysis are:
i) Gravimetric analysis, or quantitative estimation by weight, is the process of isolating and weighting an element or a compound of the element in as pure form as possible. The main object in gravimetric analysis is the transformation of the element or radical into a stable, pure compound which can be readily converted into a form suitable for weighting. The weight of the element is calculated from the formula of the compound and atomic weights of the elements that are constituents of the compound. The separation of the element or its compound may be accomplished by precipitation methods, volatilization or electroanalytical methods.
ii)Volumetric (titrimetric) analysis,is the analysis in which we measure the volume of a reagent reacting stoichiometrically with the analyte. It first appeared as an analytical method in the early eighteenth century and initially did not receive wide acceptance. The growth and acceptance of volumetric methods requireda deeper understanding of stoichiometry, thermodynamics and chemical equilibria. By the early 20thcentury the accuracy and precision of volumetric methods were comparable to that of gravimetric methods, establishing an accepted analytical technique. Titrimetric methods are classified into four categories based on the type of reaction involved: Acid-base, complexometric, redox and precipitation titrations.
Ininstrumental proceduresthere is use of instruments of some sort either to make a critical measurement or to perform the entire analysis. Modern day analytical chemistry is performed with the aid of instruments such as: NMR Spectrometer,Mass Spectrometer, FT-I.R,Gas ChromatographorLiquid Chromatograph, ICP,Craphite Furnace Atomic Absorption Spectrometer,Atomic Absorption Spectrometer, XRF, Cyclic Voltametry.
Optical methodsof analysis are also called spectroscopic methods. The first instruments were developed for use in the visible region and therefore the methods were called optical methods. All spectroscopic methods are based on the interaction of electromagnetic radiation with the quantized energy states of the matter. By these methods, we study the measurement of a quantity based on emission, absorption, scattering or change in some property of electromagnetic radiation depending on the nature or the amount of the constituent on the sample. These methods are classified based on either the type of effect (emission, absorption or scattering) or the type of the electromagnetic radiation (IR, visible, x-ray). The most important spectroscopic methods are given below:
Atomic AbsorptionSpectroscopy – Flame Photometry – Atomic Fluorescence Spectroscopy
Emission Specroscopy
Raman Spectroscopy
Microwave Spectroscopy
U.V. Absorption Spectrophotometry
Infrared Spectrophotometry
Fluorophotometry - Phosphorimetry
Turbidimetry – Nephelometry
Refractometry - Interferometry
Raman Spectroscopy
X-ray: Absorption, Emission, Diffraction
Nuclear Magnetic Resonance Spectroscopy – Electron Spin Resonance Spectroscopy
Gamma-ray Spectroscopy – Mossbauer Spectroscopy
References
1D. Harvey,“Modern Analytical Chemistry”, McGraw-Hill Companies Inc., 2000
2R.D. Brown, “Introduction to Chemical Analysis”, McGraw-Hill Companies Inc.,
1982
3S.M. Khopkar, “Basic Concepts of Analytical Chemistry” , New Age Int. Ltd. Publishers, 2nd,1998
Chapter 1
Introduction to Analytical Chemistry
Chemistry:Chemistry is that branch of science which deals with the study of matter. Anything that having mass and occupy space is called matter. There are four different types of matter i.e. Gas, liquid, solid and plasma. Gas is that type of matter having no proper shape and no proper volume i.e. air, nitrogen gas etc. Liquid is that type of matter having proper volume but no proper shape adopt the shape of the pot in that it is putted like water, milk etc. Solid is that type of matter having proper shape and proper volume i.e. stone, book, wood etc.
Plasma is that type of matter which is in between solid and liquid. It is found on sun.
ANALYTICAL CHEMISTRY: The Science of Chemical Measurements.
Or
Analytical chemistry is that branch of chemistry which deals with the analysis or characterization of analyte species. Analyte is that species which is under consideration or observation or about that we don’t know. Its chemical composition is unknown to us.
The process that we are using to get know about the chemical composition of analyte species is called analysis. In analytical chemistry there are two types of analysis, one is known is qualitative analysisand the other type is calledquantitative analysis.
Qualitative analysis is used for identification or knowing the chemical nature of the analyte speciesfrom which the analyteis made up, while the quantitative analysis is used to know about the unknown amount of analyte species.
2.)Types of Questions asked in Analytical Chemistry
a.) What is in the sample? (Qualitative analysis)
b.) How much is in the sample? (Quantitative analysis)
c.) How pure is it? (Separation analysis)
Analysis can be done with the help of using analytical techniques. Analytical techniques are valid procedures that are used for analysis. There are two groups of analytical techniques. One group is called as Qualitative analytical techniques used for identification of chemical nature of analyte species i.e. salt analysis, FTIR analysis, NMR analysis. While the other group of analytical techniques called Quantitative analytical techniques used to know about the unknown amount of analyte. Quantitative analytical techniques are further sub classified into classical techniques, while the other group of Quantitative analytical techniques is called Instrumental techniques. In case of classical techniques simple equipments like burette, pipette, flasks, cylinder, balance etc are used, while in case of Instrumental techniques the modern instruments are used to do analysis.
Classical techniques are further sub classified as volumetric techniques, gravimetric techniques and separative techniques, while the instrumental techniques are sub classified as spectroscopic techniques, electroanalytical techniques and separative techniques.
Volumetric techniques consist of a group of classical techniques based on volume measurement therefore are called as volumetric techniques, it include acid base titration (neutralization titration), redox titration, precipitation titration and complexomtric titration.
Gravimetric techniques is another class of classical techniques based on mass measurement like precipitation, volatilization etc.
While the 3rd group of classical techniques is based on separation for purification purposes include distillation, filtration, crystallization, sublimation, solvent extraction, chromatography, electrophoresisetc.
Instrumental Techniques: It is a group of Quantitative analytical techniques used for analysis of analyte species and can be practiced by using some instruments. Instrumental techniques are further sub classified as spectroscopic techniques, electroanalytical techniques and separative techniques.
Spectroscopic techniques are that kind of instrumental analytical technique in which spectrophotometer isused as an instrument and it is used both for identification as well quantification (determination the unknown amount) of analyte. It is based on interaction of electromagnetic radiations with matter. Some time the matter absorbs or sometimes emits radiations. So in spectroscopy we measure the magnitude of absorbed or emitted radiations and then relate that magnitude of radiations with the concentration of analyte species.
Electroanalytical techniques include a group of instrumental techniques like potentiometry, voltammetry, conductometry, coulometry, electrogravimetry in all those techniques there is interaction of electricity with matter and in all the above mentioned techniques we measure the electrochemical properties like potential, current, charge etc with help of different instruments like potentiometer, pH meter, conductometer, voltammeter etc,.
Separative techniques are that group of instrumental technique in that the instruments like HPLC, GC, Ion chromatograph etc are used for separation, purification identification as well as quantification of analyte specie.
Units of Concentration
Percentage Solution (%)
In order to prepare solutions of higher concentrations we use the units of percentage. There are three types of percentage Solution i.e. weight/volume, weight/ weight and volume/volume.
a) Percentage Solution Weight/Volume
Percentage Solution weight/volume meant how much weight of solute is dissolved in 100mL volume of solution.
Example: Calculate the mass in grams for preparation 5% solution of NaOH of 250mL volume.
Solution:
As we know 5% solution of NaOH meant 5grams of NaOH have dissolved in 100mL volume of solution. Now to calculate the mass in grams for 250mL volume we can do it with the help of dimensional analysis i.e. similar units cancel each others
So weight of NaOH = 12.5g
It means to prepare 250mL volume of 5% NaOH solution we need to dissolve 12.5g of NaOH and then dilute it with distilled water upto 250mL volume.
b) Percentage Solution Weight/Weight
Percentage Solution weight/weight meant how much weight of solute is mixed with 100g weight of mixture.
Example: Calculate the mass in grams for preparation 5% mixture in NaCland sand of 500grams weight.
Solution:
As we know 5% mixture in NaCland sand meant 5grams of NaClhave mixed with 95grams of sand and the total weight of mixture is 100g. Now to calculate the mass in grams for 500g mixture we can do it with the help of dimensional analysis i.e.
So weight of NaCl = 25g
It means to prepare 500g mixture of 5% NaCl we need to mix 25g weight of NaCl and 475g weight of sand.
c) Percentage Solution Volume /Volume
Percentage Solution volume/volume meant how much volume of solute is dissolved in 100mL volume of solution.
Example: Calculate the volume in mL for preparation 5% solution of HCl of 250mL volume.
Solution:
As we know 5% solution of HClmeant 5mL of HClhave dissolved in 100mL volume of solution. Now to calculate the volume in mL for 250mL volume we can do it with the help of dimensional analysis i.e.
So volume ofHCl = 12.5mL
It means to prepare 250mL volume of 5% HClsolution we need to dissolve 12.5mL of HCland then dilute it with distilled water upto 250mL volume.
Parts per million(PPm)
Parts per million (PPm) is also a unit of concentration used for preparation of solutions containing trace amount of solute.Parts per million meant how many parts of solute are present in one million parts of solution.
For example NaOH solution having concentration 1000ppm. It means that there are 1000 molecules of NaOH are present or dissolved in one million molecules of solution.
It can be prepared as below
1ppm= 1µg/ml or 1ug/g
1000ppm= 1000µg/ml
Applications:For example some body asked to prepare 1000ppm KMnO4 solution of 100ml volume.
To prepare this solution we need to calculate weight in grams of KMnO4
As we know
1ppm= 1µg/ml
So substitute the values in above expression as
As we know
µ= 10-6
So put it in the above expression
Dissolve 0.1g of KMnO4and dilute it upto 100mL volume with distilled water, so its concentration will be 1000ppm.
Parts per billion(PPb)
Parts per billion (PPb) is also a unit of concentration used for preparation of solutions containing trace amount of solute.Parts per billion meant how many parts of solute are present in one billion parts of solution.
For example NaOH solution having concentration 1000ppb, it means that there are 1000 molecules of NaOH are present or dissolved in one billion molecules of solution.
It can be prepared as below
1ppb= 1ng/ml or 1ng/g
1000ppb= 1000ng/ml
Applications:For example some body asked to prepare 1000ppb KMnO4 solution of 100ml volume.
To prepare this solution we need to calculate weight in grams of KMnO4
As we know
1ppb= 1ng/ml
So substitute the values in above expression as
As we know
n= 10-9
So put it in the above expression
Dissolve 1 x 10-4g of KMnO4and dilute it upto 100mL volume with distilled water, so its concentration will be 1000ppb.
Concentration is the ratio between the amount of solute and solvent. Solution is a mixture of solute and solvent. In analytical chemistry for analysis solutions of different concentrations are used. To prepare solutionsof different concentrations there are different types of concentration units like molarity, normality, formality, molality, %age solutions, ppm (parts per million), ppb (parts per billion) etcare used in analytical chemistry.
Molarity
It is a unit of concentration and is denoted by“M”. It can be defined as the number of moles of solute dissolved per unit volume of solution
Mole is unit of amount and can be defined as
Substituting the values of no of moles of solute in above equation so
Rearranging the above expression as
As we know
1L = 1000ml, so replace volume in letter by volume in mL in above expression like this
Applications:The above expression is generally applied to calculate the weight in grams of solute for preparation of solutions of different concentrations in molarity and volumes of analyte like this.
Example: 1.1. Prepare 0.1M NaOH solution of 250ml volume.
Toprepare 0.1M NaOH solution of 250ml volume, the job is to calculate weight of NaOH. It can be calculated by using the above express as
As we know Molecular Mass of NaOH = 23+16+1 = 40amu
So feed the values in the above expression as
Weight in grams of NaOH = 1g
It means to prepare 0.1M solution of NaOH of 250ml volume capacity we need to dissolve 1gram weight of NaOH that we calculated with the help of above expression
Normality
It is also a unit of concentration and denoted by N. It can be defined as the numberof equivalents of solute dissolved per unit volume of solution
Equivalent is also a unit of amount and can be defined as
Equivalent mass can be defined as molecular mass of the analyte divided by number of reacting units as
Number of reacting units in case of acid base reaction called to number of hydrogen or hydroxyl ions per molecule, while in case of oxidation reduction the no of electron lost or gained by an atom or molecule.
Substituting the values of number of equivalents of solute in above expression so
Rearranging the above expression as
Weight in grams of solute = Equivalent mass of solute x N x Volume in L
As we know
1L = 1000ml, so replace volume in letter by volume in mL in above expression like this
Applications:
The above expression is used to calculate weight in grams of solute for different concentrations and volumes of analyte like this.
Example: 1.2. Prepare 0.1N H2SO4 solution of 250ml volume.
Solution:
This example can be solved by using expression as we know
As H2SO4 molecule containing 2 H+ so it equivalent mass will be as
Molecular mass of H2SO4 = 98amu, so put this value in above expression
Equivalent mass=49
So put the values in above expression as
Weight in grams of H2SO4= 1.22g
As H2SO4 is a liquid in case of liquids instead of mass we are taking volume, so to calculate the volume we should use expression of density as
Rearranging the above expression as below
Substituting the values
Volume in mL = 2.24mL
But we know the percent purity of available H2SO4 is 98%. It means if we need 98mL of pure H2SO4 that will be present in 100mL of available bottle H2SO4. Now 2.24mL of pure H2SO4 will be present in how much volume of bottle H2SO4?
We can calculate it with the help of dimensional analysis i.e.
It means to prepare 0.1N H2SO4solution of 250ml volume capacity we need to dissolve 2.29ml of available bottleH2SO4.
Units of Amount
Amount is that mass of solute which containing know number of particles i.e. atoms, ions or molecule. In analytical chemistry different units of amount like mole, equivalent and formals are used.
Mole:
Mole is a unit of amount and can be defined as, one mole is that amount which containing Avogadro number (6.0221415 × 1023) of particles. It can be also defined as when the atomic mass of an atom or ion or molecular mass of a molecule is expressed in grams, then that gram atomic or molecular mass is called one mole amount and it will be containing Avogadro number of particle.
Examples:
Carbon = 12amu= 12g = 1mole = 6.0221415 × 1023 carbon atoms
Sodium ion = 23amu= 23g = 1mole = 6.0221415 × 1023Na+
Water = 18amu= 18g = 1mole = 6.0221415 × 1023H2O molecules
In analytical Chemistry number of moles is calculated as below
Examples:Calculate the number of moles for 4g mass of NaOH.
Solution:
Using the above expression as we know
As we know Molecular mass of NaOH = 23+16+1 = 40amu
Put the values in the above expression
Number of moles of NaOH = 0.1 moles
It will be containing (0.1 x 6.0221415 × 1023) = 6.0221415 × 1022 molecules of NaOH
In case of solutions number of moles is calculated as
Example:Calculate the number of moles for a solution having concentration 0.1M and its total volume is 250mL.
Solution:As we know
So putting the values in this expression as
Equivalent:
Equivalent is also a unit of amount and it can be defined as, one equivalent is that amount which containing Avogadro number (6.0221415 × 1023) of reactive specie. In case of acid base reaction reactive specie is hydrogen ion (H+) for acid and hydroxyl ion (OH-) for base, while in case of redox reaction the reactive specie is the number of electron lost or gained. In analytical chemistry number of equivalent can be calculated as below
Equivalent mass can be defined as molecular mass of the analyte divided by number of reacting units as
Number of reacting units in case of acid base reaction is the number of hydrogen or hydroxyl ions per molecule, while in case of oxidation reduction is the number of electron lost or gained by an atom or molecule.
Examples:Calculate the number of moles for 8g mass of Na2CO3.
Solution:
Using the above expression as we know
As we know Na2CO3 on hydrolysis produce two hydroxyl ions so it
It means 53g ofNa2CO3 containing Avogadro number (6.0221415 × 1023) of hydroxyl ion (OH-)
Now
In case of solutions number of equivalent is calculated as
Example:Calculate the number of equivalents for a solution having concentration 0.1N and its total volume is 250mL.
Solution:As we know
So putting the values in this expression as
Dilution Formula
In some cases concentrated solutions are prepared and then with the help of dilution formula from those concentrated solutions dilute solutions of our required concentrations are prepared i.e.
Example: How much volume of 1000ppm KMnO4 solution is required to prepare 100ppm dilute KMnO4 solution of 100mL volume?
Solution:
As we know the dilution formula is
Now substituting the values in the above expression as below
V1 = 10mL
It means take 10mL volume from 1000ppm stock or concentrated solution and then transfer it into 100mL volumetric flask and dilute it with distilled water its final concentration will be 100ppm.
Stoichiometry
The shortest representation of a chemical reaction in terms of formula of compounds is called chemical equation, while the shortest representation of a balanced chemical equation in terms of units of amount is called as stiochiometry.e.g.