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STD 12 -1. Solution and colligative properties — JEE STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceJEESTD 12 -1. Solution and colligative properties4 Marks
MCQ
An ideal solution was obtained by mixing methanol and ethanol. If the partial vapour pressure of methanol and ethanol are $2.619\,kPa$ and $4.556\,kPa$ respectively, the composition of the vapour (in terms of mole fraction) will be
  • A
    $0.635 $  methanol, $ 0.365$ ethanol
  • ✓
    $0.365$  methanol, $0.635 $ ethanol
  • C
    $0.574 $ methanol, $0.326 $ ethanol
  • D
    $0.173 $ methanol, $0.827 $ ethanol
✓

Answer

Correct option: B.
$0.365$  methanol, $0.635 $ ethanol
b
Partial pressure of methanol $=2.619\, kPa$

Partial pressure of ethanol $=4.556 \,kPa$

Total pressure $=$ Partial pressure of methanol $+$ Partial pressure of ethanol

Total pressure $=2.619+4.556=7.175\, kPa$

$X _{\text {methanol: }}$ : Mole fraction of methanol

$X _{\text {ethanol: }}$ : Mole fraction of ethanol

The partial pressure of methanol $= X _{\text {methanol }} \times$ Total pressure

$\therefore X _{\text {methanol }}=\frac{2.619}{7.175}$

$=0.365$

$\therefore$ Mole fraction of ethanol $= 1 -$ Mole fraction of methanol

$=1-0.365$

$=0.635$

Hence, the correct option is $B$.

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