Question

If sodium sulphate is considered to be completely dissociated into cations and anions in aqueous solution, the change in freezing point of water (DTf), when 0.01 mole of sodium sulphate is dissolved in 1 kg of water, is (Kf = 1.86 K kg mol–1)

• A. 0.0372 K
• B. 0.0558 K
• C. 0.0744 K
• D. 0.0186 K

Answer 1

Answer: (B)

0.0558 K

Answer 2

Na2SO4 (s) $\overset{\quad H_{2}O\quad}{\rightarrow}$ 2Na+ (aq.)+ SO42– (aq.)

$\Delta$Tf = i Kfm

= 3 ´ 1.86 ´ 0.01

= 0.0558 K.