Calculate (a) molality (b) molarity and (c) mole fraction of KI if the density of 20% (mass/mass) aqueous KI is 1.202 g mL^-1.

(a) Molality, also called molal concentration, is a measure of the concentration of a solute in a solution in terms of amount of substance in a specified amount of mass of the solvent.

Molar mass of KI 39 + 127 = 166 g/mol.

20% aqueous solution of KI means 200 g of KI is present in 1000 g of solution.

Therefore,

Molality =

=

= 1.506 m

∴ Molality of KI = 1.506 m

(b) Molarity is the concentration of a solution expressed as the number of moles of solute per litre of solution.

Given,

Density of the solution = 1.202 g/mL

Volume of 100 g solution =

=

= 83.19 mL

Therefore, molarity = mol/ 83.19 × 10 ^{- 3} L

= 1.45 M

∴ Molarity of KI = 1.45M

(c) Molar mass of KI 39 + 127 = 166 g/mol.

Moles of KI = 0.12 mol

Moles of water = = 4.44 mol

Therefore,

Mole fraction of KI =

=

= 0.0263

∴ Mole fraction of KI = 0.0263