Question

1.24 g of $AX_2$ (molar mass 124 g mol$^{-1}$) is dissolved in 1 kg of water to form a solution with boiling point of 100.105°C, while 2.54 g of AY_2 (molar mass 250 g mol$^{-1}$) in 2 kg of water constitutes a solution with a boiling point of 100.026°C. $Kb(H)_2$$\text(O)$ = 0.52 K kg mol$^{-1}$. Which of the following is correct?

• A. AX₂ and AY₂ (both) are fully ionised.
• B. AX₂ is fully ionised while AY₂ is completely unionised.
• C. AX₂ and AY₂ (both) are completely unionised.
• D. AX₂ is completely unionised while AY₂ is fully ionised.

Hint:

The extent of ionisation can be determined by comparing the expected boiling point elevation with the actual value, using the van't Hoff factor.

Answer 1

The Correct Option is A

- The boiling point elevation is given by $\Delta T_b = K_b \times m \times i$, where $m$ is the molality, $i$ is the van't Hoff factor (number of ions), and $K_b$ is the ebullioscopic constant.
- The observed change in boiling points for AX₂ and AY₂ suggests that both compounds are fully ionised because the observed changes in the boiling point are consistent with complete ionisation. 
Thus, the correct answer is that both AX₂ and AY₂ are fully ionised.