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  4. Rectified spirit contains 95% ethanol by mass, the mole-fraction of ethanol is

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Q. Rectified spirit contains 95% ethanol by mass, the mole-fraction of ethanol is

NTA AbhyasNTA Abhyas 2020Some Basic Concepts of Chemistry

Solution:

100 g ethanol solution contains 95 g of ethanol $\left(\right.C_{2}H_{5}OH\left.\right)$ . Therefore, the mass of water is (100 - 5) g = 5 g.

So mole fraction of ethanol

$X_{C_{2} H_{5} O H}=\frac{n C_{2} H_{5} O H}{n_{C_{2} H_{5} O H} + n H_{2} O}$

$=\frac{95 / 46}{\left(\right. 95 / 46 \left.\right) + \left(\right. 5 / 18 \left.\right)}$

$=\frac{2.065}{2.065 + 0.2778}=0.881$