Question

Elevation of boiling point of a 1 M aqueous glucose solution (density = 1.2 g/ml) is:
($K_b$ is molal boiling point elevation constant)

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

Answer 1

The correct option is D 0.98 $K_b$

Given,
Molarity of glucose solution = 1 M
Assuming 1 litre of the solution,
Volume of the solution = 1 L
Mass of the solution = 1200 g ( given density = 1.2 g/ml)
Number of moles of glucose = 1 mol
Mass of glucose = 180 g
Relation between molality and molarity may be written as:
$molality=\frac{1000\times molarity}{massofthesolution-massofthesolute}$
Elevation in boiling point is given by
$△$$T_b=i{K}_{b}m$
where,
$△$$T_b$ is the elevation in boing point
i is the van't Hoff factor
$K_b$ is the molal boiling point elevation constant
m is the molality

$△$$T_b=1$$\times$$K_b$$\times$$\frac{1000}{(1200-180)}$
$△$$T_b=0.98K_b$