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Question
The conductivity of sodium chloride at 298 K has been determined at different concentrations and the results are given below:
| Concentration/M | 0.001 | 0.010 | 0.020 | 0.050 | 0.100 |
| 102 × κ/S m−1 | 1.237 | 11.85 | 23.15 | 55.53 | 106.74 |
Calculate ∧m for all concentrations and draw a plot between ∧m and c1/2. Find the value of `∧_m^0`.
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Solution
| Concentration (M) | C1/2 (M1/2) |
κ(S m−1) | κ(S cm−1) | `Lambda_m = (kappa xx 1000)/M` (S cm2 mol−1) |
| 0.001 | 0.032 | 1.237 × 10−2 | 1.237 × 10−4 | `Lambda_m = (1.237 xx 10^-4 xx 1000)/0.001` = 123.7 |
| 0.010 | 0.100 | 11.85 × 10−2 | 11.85 × 10−4 | `Lambda_m = (11.85 xx 10^-4 xx 1000)/(0.010)` = 118.5 |
| 0.020 | 0.141 | 23.15 × 10−2 | 23.15 × 10−4 | `Lambda_m = (23.15 xx 10^-4 xx 1000)/0.020` = 115.8 |
| 0.050 | 0.224 | 55.53 × 10−2 | 55.53 × 10−4 | `Lambda_m = (55.53 xx 10^-4 xx 1000)/(0.050)` = 111.1 |
| 0.100 | 0.316 | 106.74 × 10−2 | 106.74 × 10−4 | `Lambda_m = (106.74 xx 10^-4 xx 1000)/(0.100)` = 106.7 |
When the straight line is drawn backwards, it meets the ∧m axis at 124.0 S cm2 mol−1, which is the value of `∧_"m"^0`.
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| S. No. | Conc. (M) |
k S cm−1 | ∧m S cm2 mol−1 |
| 1. | 1.00 | 111.3 × 10−3 | 111.3 |
| 2. | 0.10 | 12.9 × 10−3 | 129.0 |
| 3. | 0.01 | 1.41 × 10−3 | 141.0 |
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(c) If Rahul had used HCl instead of KCl then would you expect the ∧m values to be more or less than those per KCl for a given concentration? Justify. (2)
OR
(c) Amit a classmate of Rahul repeated the same experiment with CH3COOH solution instead of KCl solution. Give one point that would be similar and one that would be different in his observations as compared to Rahul. (2)
Discuss the variation of conductivity and molar conductivity with concentration.
