Addition of 1.0 g of a compound to 10 g of water increases the boiling point by 0.3° C. The amount of… · ABC26PH0664
Subject: Physical Chemistry · Chapter: Chemical Kinetics · Topic: Chemical Kinetics – General · Exam: JAM 2001-2022 · Marks: 2 · Difficulty: Medium
Addition of 1.0 g of a compound to 10 g of water increases the boiling point by $0.3^{\circ} \mathrm{C}$. The amount of compound needed to prepare a 500 ml or 0.1 M solution is (given : assume negligible dissociation or association of the compound, boiling point constant $\mathrm{K}_{\mathrm{b}}$ of water $=0.513 \mathrm{K} \mathrm{kg} \mathrm{mol}^{-1}$ )
(a)0.855 g
(b)17.1 g
(c)8.55 g
(d)85.5 g
Answer
Answer: C ✓ checked by 4AB · confidence high
The source book printed no answer; this one was worked out and checked — see the explanation.
Explanation
ΔT_b = K_b m ⇒ m = 0.3/0.513 = 0.585 mol kg⁻¹; in 10 g water that is 5.85×10⁻³ mol = 1.0 g ⇒ M = 171 g mol⁻¹. 500 mL of 0.1 M needs 0.05 mol = 8.55 g.