A certain non...

Question

A certain non-volatile electrolyte contains 40% carbon , 6.7% hydrogen and 53.3% oxygen . An aqueous solution containing 5% by mass of the solute boils at 100. $15^{\circ} C .$ Determine the molecular formula of the compound $(K_{b} = {0.5}^{\circ} C / m) :$

H C H O

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C H_{3} O H

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C_{2} H_{5} O H

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C_{6} H_{12} O_{6}

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Solution

The correct option is D $C_{6} H_{12} O_{6}$
(d) Mole ration of $C : H : O$ is $1 : 2 : 1$ so empirical formula is $C H_{2} O$
$m = \frac{Δ T_{b}}{K_{b}} \Rightarrow \frac{0.15}{0.51} \Rightarrow 0.294$ ;
$0.294 = \frac{50}{M} \times \frac{1000}{950}; M ≃ 180$
$(C H_{2} O)_{n} = 180$ or $30 \times n = 180$ or $n = 6$ ;
$∴$ molecular formula is $C_{6} H_{12} O_{6}$ .

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