AP EAPCET 04-Jul-2022 Shift 1 Paper

Given, mass of non-volatile solid =xg
Molar mass =78gmol−1
Mass of water =0.5‌kg
Kf( water )=1.86Kkg−1mol−1
Lowering in freezing point, ∆Tf=1∘C
Using the equation;
∆Tf=Kfm⇒m=‌

∆Tf

Kf

Now, substituting the given values in above formula,
m=‌

1

1.86

‌kg
We know that molality
=‌

‌ Number of moles of solute ‌

‌ Mass of solvent (in ‌kg‌ ) ‌

‌‌

n

M

=‌

1

1.86

[n = number of moles of solute
M = mass of solvent in kg ]
‌ So, ‌n=‌

1

1.86

×0.5‌=‌

0.5

1.86

‌

x

78

‌=‌

0.5

1.86

⇒‌‌x‌=‌

0.5×78

1.86

x‌=20.96g