Solutions Question 66
Question: What is the freezing point of a solution containing $ 8.1,g,HBr $ in $ 100g $ water assuming the acid to be 90% ionised $ (K_{f} $ for water $ =1.86,K,mol{e^{-1}}) $ [BHU 1981; Pb CET 2004]
Options:
A) $ {{0.85}^{o}}C $
B) $ -{{3.53}^{o}}C $
C) $ 0^{o}C $
D) $ -{{0.35}^{o}}C $
Show Answer
Answer:
Correct Answer: B
Solution:
$ \underset{(1-\alpha )}{\mathop{HBr}}, $ ⇌ $ \underset{\alpha }{\mathop{{H^{+}}}},+\underset{\alpha }{\mathop{B{r^{-}}}}, $ Total = 1 + a \ $ i=1+\alpha =1+0.9=1.9 $
$ \Delta T_{f}=i,K_{f}\times m=1.9\times 1.86\times \frac{8.1}{81}\times \frac{1000}{100}={{3.53}^{o}}C $
$ T_{f}=-{{3.53}^{o}}C $ .
