1. Tardigrade
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  3. Chemistry
  4. The vapour pressure of pure benzene at a certain temperature is 650 mm Hg. A non-volatile and non-electrolyte solid weighing 1.54 g is added to 26.00 g of benzene. The vapour pressure of the solution is 600 mm Hg. The molecular weight of solid substance isg mol- 1 Give your answer as the nearest integer.

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Q. The vapour pressure of pure benzene at a certain temperature is $650\,mm$ Hg. A non-volatile and non-electrolyte solid weighing $1.54\,g$ is added to $26.00\,g$ of benzene. The vapour pressure of the solution is $600\,mm$ Hg. The molecular weight of solid substance is_______g $mol^{- 1}$
Give your answer as the nearest integer.

NTA AbhyasNTA Abhyas 2022

Solution:

$\frac{p_{A}^{o} - p_{T}}{p_{A}^{o}}=\frac{650 - 600}{650}=\frac{1}{13}$
$\therefore \frac{p_{A}^{o} - p_{T}}{p_{A}^{o}}=\frac{W_{B}}{M_{B}}\times \frac{M_{A}}{W_{A}};\frac{1}{13}=\frac{1 . 54 \times 78}{M_{B} \times 26 . 00}$ ;
$\therefore M_{B}=\frac{1 . 54 \times 78 \times 13}{26 . 00}=60.06\,g\,mol^{- 1}$