In a conductometric titration, small volume of titrant of higher concentration is added stepwise to a larger volume of titrate of much lower concentration, and the conductance is measured after each addition. The limiting ionic conductivity ( 0) values (in mS m2 mol-1) for different ions in aqueous solutions are given below: array|c|c|c|c|c|c|c|c|c|c| Ions & Ag+ & K+ & Na+ & H+ & NO3- & Cl- & SO42- & OH- & CH3COO- \ 0 & 6.2 & 7.4 & 5.0 & 35.0 & 7.2 & 7.6 & 16.0 & 19.9 & 4.1 \ array For different combinations of titrates and titrants given in List-I, the graphs of ‘conductance’ versus ‘volume of titrant’ are given in List-II. Match each entry in List-I with the appropriate entry in List-II and choose the correct option.
- P-4, Q-3, R-2, S-5
- P-2, Q-4, R-3, S-1
- P-3, Q-4, R-2, S-5
- P-4, Q-3, R-2, S-1
Answer
(3) P-3, Q-4, R-2, S-5
Solution
Before the end point the titrate ion is replaced by the titrant ion; after it, the excess titrant adds ions and conductance rises.
P (KCl + AgNO3): Cl- (7.6) replaced by NO3- (7.2) → slight fall, then rise → graph 3.
Q (AgNO3 + KCl): Ag+ (6.2) replaced by K+ (7.4) → slow rise, then steeper rise → graph 4.
R (NaOH + HCl): OH- (19.9) replaced by Cl- (7.6) → sharp fall; excess H+ (35.0) → sharp rise → graph 2.
S (NaOH + CH3COOH): OH- replaced by CH3COO- (4.1) → fall; excess weak acid hardly ionises (common ion) → almost constant → graph 5.
P-3, Q-4, R-2, S-5
Answer: (C)