1 . 80g of solute A was dissolved in 62 . 5 cm ^ 3 of ethanol and...

Given

Mass of ${C}_{2}{H}_{5}OH = 62 . 5 \times 0 . 8 = 50g$

Mass of solute = 1.80 g

Depression in freezing point $∆ {T}_{f} = 156 . 0 - 155 . 1 = 0 . 9K$

We know that the depression in freezing point

${\Delta T}_{f} = {K}_{f} \times m$

$0 . 9 = 2 \times \dfrac{1 . 8 \times 1000}{{M}_{w} \times 50}$

${M}_{w} = \dfrac{2 \times 1 . 8 \times 1000}{0 . 9 \times 50} = 80$