45 g of ethylene glycol (molar mass 62 g/mol) is mixed with 600 g of water (Kf = 1.86 K kg/mol). The depression in freezing point is approximately:
A1.2 K
B0.73 K
C2.2 K
D3.7 K
Answer & Solution
Correct answer: C. 2.2 K
1. Moles of glycol = $45 / 62 = 0.73$ mol.
2. Molality = $0.73 / 0.6 = 1.2$ m.
3. $\Delta T_f = K_f m = 1.86 \times 1.2 = 2.2$ K. (Option A is the molality, not $\Delta T_f$.)
_Source: NCERT Class 12 Chemistry Ch 1 "Solutions", p.19_
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