Question

The vapour pressure of pure water at ${25}^{\circ }C$ is $30mm$. The vapour pressure of $10\%\left(W/W\right)$ glucose solution at ${25}^{\circ }C$ is :

• A. $31.5mm$
• B. $30.6mm$
• C. $29.67mm$
• D. $26.56mm$

Answer 1

The correct option is C $29.67mm$

$10$% solution $\Rightarrow 10g$ of glucose , $90g$ of water in $100gm$ of solution

So, number of moles of water in $90gm$=$\frac{90}{18}=5$ moles

Number of moles of glucose= $\frac{10}{180}=0.056$ moles

So, total moles= $5+0.056=5.056$ moles

Mole fraction of water= $5/5.056=0.988$

So, final vapour pressure= $P\times X_{water}=30\times 0.980=29.6mm$

Hence, the correct option is $C$