Solutions and Colligative Properties - Result Question 27
####26. Two liquids $A$ and $B$ form ideal solution. At $300 K$, the vapour pressure of a solution containing 1 mole of $A$ and 3 moles of $B$ is $550 mm$ of $Hg$. At the same temperature, if one more mole of $B$ is added to this solution, the vapour pressure of the solution increases by $10 mm$ of $Hg$. Determine the vapour pressure of $A$ and $B$ in their pure states.
$(1982,4 M)$
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Solution:
- When 1.0 mole of $A$ is mixed with 3 moles of $B$.
$$ 550=0.25 p _A^{\circ}+0.75 p _B^{\circ} $$
When 1.0 mole of $A$ is mixed with 4 moles of $B$.
$$ 560=0.20 p _A^{\circ}+0.80 p _B^{\circ} $$
Now, solving (i) and (ii) $p _A^{\circ}=400 mm$
$$ p _B^{\circ}=600 mm . $$
