Quantitative estimation of copper (II), calcium (II) and chloride from a mixture:

Quantitative estimation of copper (II), calcium (II) and chloride from a mixture:

In this experiment the chloride ion is separated by precipitation with silver nitrate and estimated. Whereas copper(II) is estimated by iodometric titration and Calcium by complexometric titration

Iodometric estimation of copper (II):

Copper solution oxidizes potassium iodide and liberates iodine; liberated iodine is estimated by sodium thiosulphate. The reactions involved are:

2 Cu2+ + 4I- à 2Cu+ + 2I2        and     2I2 + 2S2O3 ^2-  à 2I- + S4O6^2-

Complexometric estimation of calcium (II):

During the complexometric titration of calcium (II), copper (II) ion can interfere if eriochrome black-T indicator is used. So copper (II) is reduced to copper (I) by using hydrazine hydrate and precipitated as copper thiocyanate by using ammonium thiocyanate. A calcium (II) ion is then titrated with ethylene diamine tertraceetic acid (EDTA).

Ca2+ + H2 Y2- à CaY2- + 2H+ , where YH4 is EDTA

No sharp end point can be obtained for calcium (II) with eriochrome black-T indicator, so small amount of Mg-YH2 should be added to get a sharp end point.

Gravimetric estimation of chloride:

Chloride can be estimated gravimetrically by precipitating it as silver chloride. An aqueous solution of chloride is generally acidified with dilute nitric acid to prevent precipitation of other silver salts.

AgNO3 + Cl-  à AgCl (s)

Requirements:

1. Stock solution of Cu2+, Ca2+ and Cl- ions. 7. Ammonium thiocyanate

2. Sodium thiosulphate 8. Ethylene diamine tetra acetic acid

3. Starch solution 9. Hydrazine hydrate

4. Potassium iodide 10. Ammonia buffer

5. Erichrome Black-T 11. Silver nitrate

6. Nitric acid

Procedure:

Estimation of copper (II):

Take stock solution (25 ml) in a conical flask (250 ml) and add potassium iodide (1 g) to it. Iodine is liberated in the solution. Titrate the liberated iodine with standard sodium  thiosulphate solution (0.1M).

Estimation of calcium (II):

Take stock solution (25 ml) in a conical flask (250 ml). Add hydrazine hydrate (1 drop), a colourless solution will be observed. To this, add a solution of ammonium thiocyanate or potassium thiocyanate (10%, 5 ml) and filter the white precipitate. Take the filtrate in a conical flask and add ammoniaammonium chloride buffer solution (2 ml, pH=10) and add Mg-EDTA (1 ml) to the filtrate. Titrate the solution with standard EDTA (0.01 M solution) using eriochrome black-T indicator. Calculate the amount of calcium in wt / lit and also express it as ppm.

Estimation of chloride:

Take stock solution (25 ml) in a conical flask. Acidify the solution with dilute nitric acid (1M, 10 ml), and then add silver nitrate solution (0.2 g / ml water). This will give a white precipitate of silver chloride. Filter the precipitate in a preweighed crucible. Place the crucible along with the precipitate in an oven (~ 500C) for 1hr after that cool the crucible to room temperature and weigh. Repeat the process of heating and weighing till constant weigh is obtained. Find out the weigh of silver chloride formed and find out the amount of silver.

Some Experiments in Inorganic Chemistry

COMPILED BY:

Prof. J.B.BARUAH

Mr. Parikshit Gogoi and Mrs. Abhilasha Mohan Baruah