Question

How many grams of sucrose must be added to $320g$ of water to lower the vapour pressure by $1.5mm$ $Hg$ at ${25}^{o}C$?
(Given: The vapour pressure of water at ${25}^{o}C$ is $23.8mm$ $Hg$ and molar mass of sucrose is $324.3g/mol$)

• A. $21.5g$
• B. $140g$
• C. $363.36g$
• D. $160.12g$

Answer 1

The correct option is C $363.36g$

$w_1=$ Wsucrose = ?

$M_1=$ Molecular weight $+32,4.3g/mol$

$w_2=320g$

$M_2=H_{2}O=18g/mol$

$p-ps=1.5mm$

$p=23.8mm$

$\frac{p-ps}{p}=\frac{W_1}{M_1}\times \frac{M_2}{W_2}$

$\frac{1.5}{23.8}=\frac{W_1}{324.3}\times \frac{18}{320}$

$W_1=363.36g$