The method to determine the exact amount of the substance in a given sample is termed as quantitative analysis volumetric analysis is a branch of quantitative analysis involving accurate measurement of volumes of reacting solutions. The volumetric analysis is very much in use due to simplicity rapidity accuracy and wide applicability. The reacting substances are taken in the form of solutions and made to react. The concentration of one solution is determined using another suitable solution whose concentration is accurately known. A known volume of one solution is measured with a pipette and taken in a conical flask. The other solution is taken in a burette and run into the first solution till the chemical reaction is just complete. The volume of the second solution is read from the burette and the two volumes are compared. Various terms used in volumetric analysis are given below: Titration The process of adding one solution from the burette to another in the conical flask in order to complete the chemical reaction is termed titration. Endpoint It is the exact stage at which chemical reaction involved in the titration is just complete Indicator It is a substance which will show the end point of the reaction by change of colour. For example phenolphthalein and methyl orange are indicators used in acid alkali titrations. Potassium permanganate itself acts as an indicator in potassium permanganate titrations. Acidimetry and Alkalimetry Titration: Acidimentry refers to the titration of alkali with a standard acid and alkalimetry refers to the titration of an acid with a standard alkali. 123
Permanganimetry Titration: The titration involving KMnO4 is called permanganimetry titration. In presence of dilute H2SO4 KMnO4 oxidizes ferrous sulphate to ferric sulphate and oxidizes oxalic acid to CO2 and H2O. Normality: The strength of a solution is expressed in terms of normality. Normality is the number gram equivalent mass of solute dissolved in one litre of solution. Standard solution: A solution of known strength (Normality) is called a standard solution. Decinormal Solution: A solution having the strength (Normality) of 0.1 N is called decinormal solution. Law of volumetric analysis: Whenever two Substances react together, they react in the ratio of their equivalent mass. One litre of a normal solution of a substance will react exactly with same volume of a normal solution of another substance. In other words equal volumes of equal normal solutions will exactly react with each other. This result is stated in the form law of volumetric analysis If V1 ml of a solution of strength N1 is required or complete reaction by V2 ml of the second solution of strength N2 then V1N1=V2N2 If any three factors (V1V2 & N1) are known, the fourth factor N2 can be calculated. The following are the important formula used in all volumetric estimations Mass of solute per litre of the solution = Equivalent mass x Normality
Equivalent mass of some important compounds
Name of the compound Hydrochloric acid Sulphuric acid Oxalic acid Sodium carbonate Sodium hydroxide Potassium hydroxide Potassium permanganate Ferrous sulphate Ferrous ammonium sulphate Potassium dichromate Copper sulphate EDTA (disodium salt)
Equulvalent Mass 36.5 49 63 53 40 56.1 31.6 278 392 49.04 249.54 372
1 ESTIMATION OF SULPHURIC ACID
EX.NO................... Date.............. Aim To estimate the amount of Sulphuric acid present in 400 ml of the given solution. You are provided with a standard solution of oxalic acid of normality ..............N and an approximately decinormal solution of Sodium hydroxide. (Test solution should be made up to 100 ml) Principle The titration is based on the neutralisation reaction between oxalic acid and Sodium hydroxide in titration I and Sulphuric acid and Sodium hydroxide in titration II. Procedure Titration I: Standardisation of Sodium hydroxide The burette is washed...