1

### AIPMT 2015 Cancelled Paper

Which of them is not equal to zero for an ideal solution?
A
$\Delta {V_{mix}}$
B
$\Delta P = {P_{observed}} - {P_{Raoult}}$
C
$\Delta {H_{mix}}$
D
$\Delta {S_{mix}}$

## Explanation

For an ideal solution, $\Delta$Smix > 0 while $\Delta$Hmix, $\Delta$Vmix and $\Delta$P all are 0.
2

### AIPMT 2015

What is the mole fraction of the solute in a 1.00 m aqueous solution?
A
1.770
B
0.0354
C
0.0177
D
0.177

## Explanation

Number of moles of water in 1000 g = ${{1000} \over {18}}$ = 55.56 mol

Thus, mole fraction of solute = ${1 \over {1 + 55.56}}$ = 0.0177
3

### AIPMT 2015 Cancelled Paper

The boiling point of 0.2 mol kg$-$1 solution of X in water is greater than equimolal solution of Y in water. Which one of the following statements is true in this case?
A
Molecular mass of X is less than the molecular mass of Y.
B
Y is undergoing dissociation in water while X undergoes no change.
C
X is indergoing dissociation in water.
D
Molecular mass of X is greater than the molecular mass of Y.

## Explanation

$\Delta$Tb = iKbm

Given, ($\Delta$Tb)x > ($\Delta$Tb)y

$\therefore$ ixKbm > iyKbm

$\Rightarrow$ ix > iy

(Kb is same for same solvent)

So, x is undergoing dissociation in water.
4

### AIPMT 2014

Of the following 0.10 m aqueous solutions, which one will exhibit the largest freezing point depression?
A
KCl
B
C6H12O6
C
Al2(SO4)3
D
K2SO4

## Explanation

We know that depression in freezing point ($\Delta$Tf ) is given as

$\Delta$Tf = iKfm

So, $\Delta$Tf $\propto$ i

Thus, more value of i (Van’t Hoff factor), more will be depression in freezing point.

Al2(SO4)3 ⇌ 2Al+3 + 3SO42–

i is maximum i.e., 5 for Al2(SO4)3. .