Question

The elevation in the boiling point of one molar aqueous solution of glucose is:
(density = 1.2 g/mL)

• A. $1K_b$
• B. $1.20K_b$
• C. $1.02K_b$
• D. $0.98K_b$

Answer 1

The correct option is D $0.98K_b$

We know,
$\Delta T_b=i{K}_{b}m$
for glucose $i=1$
1 molar aqueous glucose solution = 1 mole of glucose present in 1000 mL of solution.
Mass of 1000 mL solution = 1200 g (from given density)
we know, molality $=\frac{molofsolute}{kgofsolvent}$
So, weight of solvent = $(1200-180)g$ (since 1 mole of glucose = 180 g of glucose)
$\Delta T_b=1\times K_b\times \frac{1}{\frac{1200-180}{1000}}$
$=1\times K_b\times \frac{1000}{1200-180}$
$=0.98K_b$