6. Estimation of copper content of the given solution by iodometry

6. ESTIMATION OF COPPER CONTENT OF THE GIVEN SOLUTION BY IODOMETRY

Expt. No.

Date:

AIM

To estimate the amount of copper present in the given solution by iodometric titration. You are provided with standard ......... N K₂Cr₂O₇ solution.

PRINCIPLE

Copper ion occurs naturally in drinking water and is a micronutrient required for the metabolism of living beings. But the presence of copper in water,in quantities more than 1.3 mg/l, will cause stomach ache, intestinal distress and digestive problems. High concentration of copper will also impart a metallic bitter taste to water. Occurrence of copper ions in drinking water may be due to corrosion in plumbing materials and faulty water treatment processes. Copper is also known to cause toxicity to aquatic organism.

Titrimetric estimation of copper is done through a redox reaction in which stoichiometric quantity of iodine is liberated on reaction with potassium iodide. The liberated iodine can be titrated against standardised sodium thiosulphate solution.

When KI is added to the copper ion solution, copper ions react with KI and liberates I₂.

2CuSO₄ + 4KI → 2K₂SO₄ + 2CuI + I₂ ↑

The liberated I₂ is titrated against sodium thiosulphate, using starch indicator.

TITRATION II: ESTIMATION OF COPPER CONTENT OF THE GIVEN

SOLUTION

Given copper ion solution Vs sodium thiosulphate solution

CALCULATION

Volume of sodium thiosulphate solution (V₁) = ...... ml

Strength of sodium thiosulphate solution (N₁) = ...... N

Volume of the given copper ion solution (V₂) = 20 ml

Strength of the given copper ion solution (N₂) = ?

According to the law of volumetric analysis, V₁ N₁ = V₂N₂

PROCEDURE

TITRATION I

Standardisation of sodium thiosulphate

20 ml of standard potassium dichromate solution is pipetted out into a clean conical flask. About 10 ml of dilute H2SO4 and 10 ml of 10% KI are added to it. The liberated iodine is immediately titrated against sodium thiosulphate solution taken in the burette. When the solution turns pale yellow, about 1 ml of freshly prepared starch is added and the titration is continued. The end point is the disappearance of blue colour. Titration is repeated for concordant values.

TITRATION II

Estimation of copper ion content of the given solution

20 ml of the given copper ion solution is pipetted out into a clean conical flask. About 10 ml of dil. H₂SO₄ and 10 ml of 10% KI solutions are added to this solution and the liberated iodine is titrated against standardised sodium thiosulphate taken in the burette. When the solution turns pale yellow, about 1 ml of freshly prepared starch indicator is added and the titration is continued. The disappearance of blue colour is the end point. The titration is repeated for concordant values.

RESULT

1. Strength of the given copper ion solution =  …………. N

2. The amount of copper in the given copper ion solution = ............ g/lit

TABULATION

Calculation

Weight of residue w = W₂ - W₁

= .................... (-) ...................

= ................... gms

= × 1000 mgs

= .................. mgs

Total Dissolved Solids (mg/L)