When 2 g non-volatile hydrocarbon containing 94.4% carbon by mass is dissolved in 100 g of benzene,

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When 2 g non-volatile hydrocarbon containing 94.4% carbon by mass is dissolved in 100 g of benzene, the vapour pressure of benzene at 30°C is lowered from 89.78 mm to 89.0 mm. The molecular formula of the hydrocarbon is

Accepted Answer

$\frac{P^{o} - P}{P} = \frac{n_{1}}{n_{2}} \Rightarrow \frac{89.78 - 89}{89} = \frac{2/M}{100/78} \Rightarrow M = 178$

Now, the number of C-atoms in each molecule $= \frac{178 \times \frac{94.4}{100}}{12} = 14$

and the number of H-atoms in each molecule $= \frac{178 \times \frac{5.6}{100}}{1} = 10$

∴ Hydrocarbon is C₁₄H₁₀.

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