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CONDUCTOMETRY

AIM

To determine the strength of a strong acid by titrating against a strong base conductometrically.

APPARATUS

Conductivity bridge, conductivity cell, 100 ml beaker, 100 ml standard flask, microburette.

PRINCIPLE

Conductometric titrations are based on changes in the electrical conductance of a solution. A solution containing hydrochloric acid dissociates into H⁺ and Cl⁻ ions, in which H⁺ ions have greater mobility. With addition of sodium hydroxide solution, H⁺ ions are replaced by Na⁺ ions. This decreases the conductivity of the solution as Na⁺ ions possess lesser mobility. At the neutralization point, the solution contains Na⁺ and Cl⁻ ions and will show minimum conductivity. On further addition of sodium hydroxide solution, conductivity increases because of the higher mobility of the OH⁻ ions.

PROCEDURE

Take standard solutions of 1N sodium hydroxide and 0.1 N hydrochloric acid. Transfer 20 ml of the given hydrochloric acid solution into a 100 ml beaker and add 20 ml of water. Keep the beaker in thermostat. Wash the conductivity cell with the conductivity water and rinse with the acid solution. Keep the cell in an acid-containing beaker and connect to the conductivity bridge. Measure the conductivity of the solution using a digital conductometer. Add 0.2 ml of the sodium hydroxide solution into the beaker, stir well and measure the conductivity. Continue the addition of the solution (0.2 ml each time), stir well and measure the conductivity for every instance. Repeat the addition until the number of values taken on either side of the point of minimum conductivity is equal. Calculate the corrected conductance by applying volume correction, which is given by

PRECAUTIONS

1. The conductivity cell should never be kept dry.
2. The electrode must be washed.
   

CALCULATIONS

GRAPH

RESULT

The strength of hydrochloric acid is determined experimentally and is found to be _____ N.

VIVA QUESTIONS

1. What is conductometric titration?
2. What is the difference between conductometric and volumetric titrations?
3. What is the unit of conductance?
4. What is conductivity?
5. What are the factors influencing conductivity?
6. When we increase the concentration, what will happen to the conductance?
7. How can you identify the end point of titration?
8. HCl + NaOH → _____.
9. Which medium shows high conductance values?
10. What are the advantages and disadvantages of conductometric titration?
11. What is the importance of conductometric titrations?