Question

Calculate the molality of KI if the density of 20% (mass/mass) aqueous KI is 1.202 gmL^-1. Report your final answer by rounding off the molality correct upto one place of decimal and then multiplying it by 10.

Answer 1

Answer: 15.00

Weight of KI in 100g of water = 20 g

Weight of water in the solution = 100 - 20 = 80 g= 0.08 kg

Molar mass of KI = 39 + 127 = 166 g mol^-1

$\text{Molality of the solution (m)}=\frac{\text{Number of moles of KI}}{\text{Mass of water in kg}}$

$=\frac{(20\mathrm{g})/\left(166\mathrm{g}{\mathrm{mol}}^{-1}\right)}{(0\cdot 08\mathrm{kg})}$

= 1.506 mol kg^-1 = 1.506 m

By rounding off to one place, we get the molality as 1.5 and by further multiplying it with 10, we get "15" as the final answer.