10. Conductometric precipitation titration using BaCl2 - Na2SO4

10. CONDUCTOMETRIC PRECIPITATION TITRATION USING BaCl₂ - Na₂SO₄

Expt. No.

Date:

AIM

To determine the amount of BaCl2 present in the given solution by conductometric titration using standard Na2SO4 solution of ...... N.

PRINICIPLE

Solution of electrolytes conducts electricity due to the presence of ions. Since specific conductance of a solution is proportional to the concentration of ions conductance of the solution is measured during titration.

In the precipitation titration, the ions are converted into insoluble precipitate, which will not contribute to the conductance. When Na₂SO₄ is added slowly from the burette to the solution of BaCl₂, BaSO₄ gets precipitated while the chloride ions remain unchanged.

BaCl₂ + Na₂SO₄ → BaSO₃ ↓ + 2NaCl

The Ba²⁺ ions in the solution are replaced by free Na⁺ ions. Since the mobility of Nations are less than that of Ba²⁺ ions, the conductance of the solution decreases. After the end point, when all the Ba²⁺ ions are replaced, further addition of Na₂SO₄ increases the conductance. This is due to the increase of Na⁺ and SO^2-₄ ions in the solution.

MATERIALS REQUIRED

1. Conductivity bride 2. Conductivity cell 3. 100 ml beaker 4. Std. Na₂SO₄ solution 5. Given BaCl₂ solution 6. Burette, pipette, glass rod etc., 7. Distilled water.

PROCEDURE

The burette is filled with Na₂SO₄ solution upto the zero level. 20 ml of the given BaCl2 solution is pipetted out into a clean 100 ml beaker. The conductivity cell is placed in it and then diluted to 40 ml by adding conductivity water. The two terminals of the cell are connected with a conductivity bridge.

Calculation

Volume of BaCl₂ mixture  V₁ = 20 ml

Strength of BaCl₂ solution N₁ = ... ?

Volume of Na₂SO₄   V₂ = ... ml

Strength of Na₂SO₄  N₂ = ...... N

According to law of volumetric analysis V₁N₁ = V₂N₂

Now 1 ml of Na₂SO₄ from the burette is added to the solution, taken in the beaker, stirred and then conductivity is measured. This is continued up to the end point. (The conductivity is going on decreasing up to the end point). After the end point, again Na₂SO₄ is gradually added and few more readings are noted.

Thus the conductivity is continuously measured for each addition of Na₂SO₄ and are tabulated. Now the graph is plotted between the volume of Na₂SO₄ and conductivity. From the graph, end point is noted and hence the amount of BaCl₂ present in the given solution is calculated.

RESULT

The amount of BaCl2 present in the given solution = ……… gms.