Two 5 molal solutions are prepared by dissolving a non-electrolyt… - Vidyadip

MCQ

Two $5$ molal solutions are prepared by dissolving a non-electrolyte, non-volatile solute separately in the solvents $X$ and $Y$. The molecular weights of the solvents are $M_X$ and $M_Y$, respectively where $M_X\, = \frac{3}{4} M_Y$. The relative lowering of vapour pressure of the solution in $X$ is $''m''$ times that of the solution in $Y$. Given that the number of moles of solute is very small in comparison to that of solvent, the value of $''m''$ is

✓
$\frac{3}{4}$
B
$\frac{1}{2}$
C
$\frac{1}{4}$
D
$\frac{4}{3}$

✓

Answer

Correct option: A.

$\frac{3}{4}$

a
The relationship between molar masses of the two solvents is

$M_X\,=\,\frac {3}{4}M_Y$ .... $(i)$

The relative lowering of vapour pressure of two solution is

${\left( {\frac{{\Delta P}}{P}} \right)_X}\, = \,m{\left( {\frac{{\Delta P}}{P}} \right)_Y}$

But, the relative loering of vaoour pressure of solutin is directly proportional to the mole fraction of solution.

Given $5\,molal$ solution , mans $5\,molal$ of solute are dissolved in $1\,kg$ (or $1000\,g$) of solvent.

The number of moles of solvent $=\,\frac {1000\,g}{M}$

The mole fraction of solution $=\,\frac {5}{1000/M}$

$=M\times \,\frac {5}{1000}$

hence $M_X\times \frac {5}{1000}$ $=\,m\times M_Y\times \frac {5}{1000}$ .... $(ii)$

Substitute equation $(i)$ in equation $(ii)$

$\frac {3}{4}\times M_Y\times \frac {5}{1000}$ $=\,m\times M_Y\times \frac {5}{1000}$

$m=\frac {3}{4}$

Need a full question paper?

Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.

Start Generating Free

Explore more

More "M.C.Q (1 Marks)" from 1. Solution and colligative properties→1. Solution and colligative properties — all question types→Chemistry STD 12 Science question papers→CBSE Board STD 12 Science question papers→CBSE Board question paper generator→

Similar questions

Acompound of mercury used in cosmetics, in Ayurvedic and Yunani medicines and known as Vermilon is

Collision frequency of a gas at $\text{1 atm}$ pressure is $Z.$ Its value at $\text{0.5 atm}$ will be:

Which of the following ligand is not bidentate

$6.5\, g\, Mg$ deposits on electrolysis of $MgCl_2$ (fused) then what will be the volume of chlorine gas at $STP$ discharged at electrode ............ $\mathrm{L}$

White prepipitate is formed in.

The vapour pressure of water at $20\,^oC$ is $17.5\, mm\, Hg$. If $18\, g$ of glucose $(C_6H_{12}O_6)$ is added to $178.2\, g$ of water at $20\,^oC$, the vapour pressure of the resulting solution will be .......... $mm\, Hg$.

The hybridisation state of nitrogen in trimethylamine is :

Which disaccharide is present in milk?

Assertion : $HClO_4$ is a stronger acid than $HClO_3$.

Reason : Oxidation state of $Cl$ in $HClO_4$ is $+VII$ and in $HClO_3$ $+V$.

$10.6\,grams$ of a substance of molecular weight $106 $ was dissolved in $100\,ml$. $10\,ml$ of this solution was pipetted out into a $1000\,ml$ flask and made up to the mark with distilled water. The molarity of the resulting solution is