Question

Assuming ideal solution behavior, what is the boiling point of a solution of NaCl in water if the solution freezes at −0.93 °C?

a) 100.93 °C
b) 101.86 °C
c) 99.07 °C
d) 99.14 °C

Answer 1

The boiling point of a NaCl solution that freezes at -0.93 °C is approximately 100.26 °C, closest to option a) 100.93 °C, considering the molal boiling point elevation constant for water and the freezing point depression of NaCl. The correct option is a.

Step-by-step explanation:

The question asks about the boiling point elevation of a NaCl solution in water which freezes at -0.93 °C. Assuming ideal solution behavior, we know that a 1.0 m solution of NaCl will depress the freezing point by 3.7 °C.

Given that water usually freezes at 0.0 °C, a freezing point of -0.93 °C suggests a molality of around 0.5 m (since -0.93 °C is approximately half of 3.7 °C which is the depression for a 1.0 m solution).

The molal boiling point elevation constant (k) for water is 0.51°C/m, so boiling point elevation for a 0.5 m solution would be approximately 0.51°C/m * 0.5 m = 0.255 °C.

Since the normal boiling point of water is 100.0 °C, the boiling point of the solution would be 100.0 °C + 0.255 °C, which is approximately 100.26 °C. This is closest to answer choice a) 100.93 °C. The correct option is a.