Question

The depression in freezing point of $0.01 m$ aqueous $CH _3 COOH$ solution is $0.02046^{\circ} .1 m$ urea solution freezes at $-1.86^{\circ} C$. Assuming molality equal to molarity. $pH$ of $CH _3 COOH$ solution is

• A. 2
• B. 3
• C. 3.2
• D. 4.2

Answer 1

Answer: (B)

$\Delta T_{ f }=K_{ f } \times m^{\prime} \times i$
$\frac{\Delta T(\text { urea })}{\Delta T\left( CH _3 COOH \right)}=\frac{m^{\prime} \text { (urea) }}{m^{\prime}\left( CH _3 COOH \right) \times i}$
$i=1.1(i=1$ for urea)
$=(1+x)$ for $CH _3 COOH$
$x=0.1$
$\therefore\left[ H ^{\oplus}\right]=C x=0.001$
$\therefore pH =3$