KVPY2019ChemistrySolutions
The boiling point of 0 . 001   M aqueous solutions of NaCl ,   Na 2 SO 4 ,   K 3 PO 4 and CH 3 COOH should follows the order.
Options
- ACH 3 COOH < NaCl < Na 2 SO 4 < K 3 PO 4
- BNaCl < Na 2 SO 4 < K 3 PO 4 < CH 3 COOH
- CCH 3 COOH < K 3 PO 4 < Na 2 SO 4 < NaCl
- DCH 3 COOH < K 3 PO 4 < NaCl < Na 2 SO 4
Correct answer
A. CH 3 COOH < NaCl < Na 2 SO 4 < K 3 PO 4
Step-by-step solution
Elevation in boiling point, ΔT b = i × K b × m . ( K b is constant for a solvent) If molality m is same, ΔT b ∝ van't Hoff factor ( i ) CH 3 COOH only partially dissociates, ∴   i < 2 NaCl , Na 2 SO 4 and K 3 PO 4 almost completely dissociate to produce 2 , 3 and 4 ions per formula respectively, ∴   i ≈ 2 , 3 , and 4 respectively ∴ The order of i = the order of boiling points = CH 3 COOH < NaCl < Na 2 SO 4 < K 3 PO 4