Q. What is the freezing point of a solution containing 8.1 g $HBr$ in 100 g water assuming the acid to be 90% ionised ($k_{f}$ for water $= 1.86\ kg\ mol^{- 1}$)?
A) $- 0.35℃$
B) $- 1.35℃$
C) $- 2.35℃$
D) $- 3.53℃$
Explanation
(d)
[image:2_image2.emf]
$i\ Total = (1 - \alpha) + \alpha + \alpha = (1 + \alpha)$
$i = 1 + 0.9 = 1.9$
$\mathrm{\Delta}T_{f} = ik_{f}m = 1.9 \times 1.86 \times \frac{8.1}{81} \times \frac{1000}{100} = 3.53℃$
$T_{f} = T - \mathrm{\Delta}T_{f} = 0 - 3.53℃ = - 3.53℃$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.