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Question Bank [2022] — Chemistry STD 12 Science — Question

Maharashtra BoardEnglish MediumSTD 12 ScienceChemistryQuestion Bank [2022]2 Marks
Question
When $50\ gv of a nonvolatile solute is dissolved in a certain quantity of solvent, the elevation of boiling point is $2.0\ K.$ What will be the elevation of a boiling point when $30\ g$ of solute is dissolved in the same amount of the same solvent?
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Answer

Given: For $50 g$ of nonvolatile solute, $\left(\Delta T _{ b }\right)_1=2.0 K$
Mass of solute $=\left( W _2\right)_1=50 g$
Mass of solute $=\left( W _2\right)_2=30 g$
To find: Elevation of boiling point when $30 g$ of solute is dissolved
Formula: $\Delta T _{ b }=\frac{1000 K _{ b } W _2}{ M _2 W _1}$
Calculation: For $50 g$ of nonvolatile solute,
$\left(\Delta T _{ b }\right)_1=\frac{1000 K _{ b }\left( W _2\right)_1}{ M _2 W _1}$
For $30 g$ of nonvolatile solute,
$\left(\Delta T _{ b }\right)_2=\frac{1000 K _{ b }\left( W _2\right)_2}{ M _2 W _1}$
From equation (1) and (2),
$\frac{\left(\Delta T _{ b }\right)_1}{\left(\Delta T _{ b }\right)_2}=\frac{\left( W _2\right)_1}{\left( W _2\right)_2} \quad \ldots . .\left(\because K _{ b }, M _2 \text { and } W _1 \text { are constant }\right)$
$ \therefore\left(\Delta T _{ b }\right)_2=\frac{\left(\Delta T _{ b }\right)_1 \times\left( W _2\right)_2}{\left( W _2\right)_1}$
$=\frac{2.0 K \times 30 g }{50 g }=1.2 K $
Elevation of boiling point when $30 g$ of solute is dissolved is $1.2 K$.

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