Question

Calculate the molar mass of the compound used in a lab in which the following was given: -62.5 grams of an ionic solid was used to lower the freezing point of water to -1.330C.
-This compound contained 3 ions and was dissolved in 1 kg of water.

Answer 1

K_f for water is 1.853 $K\cdot{kg}\cdot{mol^{-1}}$

The freezing point depression formula is:

$\Delta{T}=iK_fm$

From this formula we can find the molality (m) - moles of a solute in 1 kg of the solvent; i stands for the number of ions produced by 1 molecule of an ionic compound.

$m=\frac{\Delta{T}}{iK_f}=\frac{0-(-1.33)}{1.853\times3}=0.239mol/kg_{solvent}$

There is exactly 1 kg of water.

Therefore, the molar mass is $\frac{62.5g}{0.239mol}=262g/mol$

Answer: 262 g/mol