CBSE Class 12 Chemistry 2023 Delhi Set 1 Solved Paper

Question : 32

Total: 35

Rahul set-up an experiment to find resistance of aqueous KCl solution for different concentrations at 298K using a conductivity cell connected to a Wheatstone bridge. He fed the Wheatstone bridge with a.c. power in the audio frequency range 550to 5000 cycles per second. Once the resistance was calculated from null point he also calculated the conductivity K and molar conductivity ∧m and recorded his readings in tabular form.

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

Answer the following questions:
(a) Why does conductivity decrease with dilution?
(b) If ∧°m of KCl is 150.0S‌cm‌mol−1 , calculate the degree of dissociation of 0.01M‌KCl .
(c) If Rahul had usedHClinstead to KCl then would you except the ∧m values to be more or less than those per KCl for a given concentration. Justify.
OR
(c) Amit, a classmate of Rahul repeated the same experiment with CH3COOH solutioninsteadof KCl solution. Give one point that would be similar and one that would be different in his observations as compared to Rahul.

Solution: 👈: Video Solution

(a) Conductivity decreases with dilution because it depends upon the number of ions present in the solution. When dilution increases number of available ions decreases. Hence, conductivity decreases.
(b) ∝=

i°m

im=150.0Scm2mol−1
i°m=141.0Scm2mol−1
∝=

141

150

=0.94
(c) Molar conductivity of HCl will be high because when it break down into ions, it produce
HCl→H++Cl−
Its H+(cation) size is smallerthen K+ion. So for same concentration of HCl and KCl,HCl shows high molar conductivity.
[OR]
(c) (i) KCl is strong electrolyte and completely dissociate into their respective ion while CH3−COOH is weak electrolyteand do not completely dissociate.
(ii) Number of ions produced after dissociation are equal
KCl→K++Cl−
CH3−COOH→CH3−COO−+H+

Go to Question:

Prev Question

Next Question