Fill in the missing information. Provide explanation and sample calculation. Thank you. Experiment No. 4

CONDUCTIMETRY: DETERMINATION OF THE ELECTRICAL PROPERTIES OF SOLUTIONS

Objectives

1. To determine the relative mobility of some monovalent ions by measuring the conductance of solutions of electrolytes.
2. To determine the dissociation constant of a weak electrolyte.

Apparatus

Conductivity meter, 50 ml beakers, 10 ml graduated cylinder

Reagents

Deionized water, 0.1M HCl, 0.1M NH₄Cl, 0.1M NaCl, 0.1M NaC₂H₃O₂, 0.1M NaOH

Procedure

1. Electrolytic Conductance and Ionic Mobility

The speed of migration of the ions is one of the factors, which determines the conductance of an electrolyte solution. The current flowing through the solution is carried by the ions moving towards the electrodes. The current flowing through the solution will be estimated by measuring the conductance of the solution through the following procedures:

1. Assemble the set up for conductance measurement.
2. Prepare 10 ml of each of the following solutions in a test tube:
   1. 0.1M ammonium chloride solution
   2. 0.1M hydrochloric acid solution
   3. 0.1M sodium chloride solution
   4. 0.1M sodium acetate solution
   5. 0.1M sodium hydroxide solution
3. Measure the conductance of each of the electrolyte solutions by immersing the electrode in the solution.
4. Wash the electrode with deionized water then dry it with a tissue paper before immersing it into another solution.

Treatment of Results

1. Write the equations for the dissociation of each of the electrolyte used.
2. Tabulate in increasing order the conductance of the solutions containing chloride ions. Infer from these results the order for the relative mobility of the cations in the solutions.
3. Tabulate in increasing order the conductance of the solutions containing sodium ions. Infer from these results the order for the relative mobility of the anions in the solutions.

2. Determination of Dissociation Constant of a Weak Electrolyte

The dissociation constant of aqueous ammonia, a weak electrolyte, will be determined through a conductimetric method. The concentration of the ions in the ammonia solution will be obtained from the concentration of a potassium hydroxide solution exhibiting the same conductance. Potassium hydroxide is a strong electrolyte whose ions exhibit the same mobility as those in aqueous ammonia. The following procedures must be followed:

1. Prepare the following mixtures in a 50 ml beaker:

MIXTURE	Vol. 0.01M KOH, ml	Vol. Water, ml
1	25.0	0.0
2	20.0	5.0
3	15.0	10.0
4	10.0	15.0
5	5.0	20.0
6	1.0	25.0

2. Measure the conductance of the above mixtures.
3. Pour 10 ml each of 1.0M and 0.1M ammonia solution into two separate test tubes, and then measure the conductance of each solution.

Treatment of Results

1. Calculate the concentration of potassium hydroxide in each of the mixtures prepared.
2. Tabulate the concentration and the conductance of the potassium hydroxide solutions.
3. Plot the concentration versus conductance of the potassium hydroxide solutions.
4. Determine from the graph the concentration of the potassium hydroxide solution that exhibits the same conductance as each of the ammonia solutions used. This concentration is equal to the concentration of ammonia ionized in the solution.
5. Write the chemical equation for the dissociation of ammonia into ions in aqueous solution.
6. Using the concentration data obtained for each of the solutions used, calculate the dissociation constant of ammonia solution.

FINAL DATA SHEET

A. Electrolytic Conductance and Ionic Mobility

Solution	Conductance, mS
0.1 M NH4Cl	14.99
0.1 M HCl	42.60
0.1 M NaCl	12.65
0.1 M NaC2H3O2	9.10
0.1 M NaOH	24.92

B. Determination of Dissociation Constant of a Weak Electrolyte

Mixture	Volume Water, mL	Conductance	Concentration	Volume 0.01M KOH, mL
1	0	8.7 mS		25
2	5	7.13 mS		20
3	10	5.27 mS		15
4	15	3.66 mS		10
5	20	1.80 mS		5
6	25	0.32 mS		1

Sample	Conductance	Dissociation Constant
1.0 M NH4OH	4.0 mS
0.01 M NH4OH	0.35 mS

Provide explanation and sample calculation. Thank you.