Question

When a mass 337 mg of an unknown compound was dissolved in 750mL of water, the solution's freezing point became -3.90 degrees C. Suppose the Kf is 1.86 degrees C/m, find the molar mass of the unknown compound.

Answer 1

$\Delta\>T_f=k_f×M$

$3.90=1.86M$

$M=2.097$

Mg of compound in 1kg of water

$\frac{1000}{750}×337=449.3$

Molar mass $=\frac{1}{2.097}×449.3$

$=214.3g$