Question

A solution of water (kf=1.86 ∘c/m) and glucose freezes at − 3.75 ∘c. What is the molal concentration of glucose in this solution? Assume that the freezing point of pure water is 0.00 ∘c.

Answer 1

Glucose freezes at -3.75 °C and freezing point of pure water is 0 °C. Thus, depression in freezing point or
`\Delta T_(f)` can be calculated as follows:

`\Delta T_(f)=0-(-3.75)^(o)C=3.75^(o)C`

It is related to molal concentration as follows:

`\Delta T_(f)=k_(f)m`

Here,
`k_(f)` is freezing point depression constant.

Rearranging to calculate molal concentration:

`m=(\Delta T_(f))/(k_(f))=(3.75 ^(o)C)/(1.86^(o)C/m)=2.02 m`

Therefore, molal concentration of glucose in the solution will be 2.02 m.