Question

Suppose that you have a 8.58 mass % solution of potassium iodide, KI, in water. What mass of solution in grams contains 10.0 g of KI?

What is the molality of a solution made by dissolving 4.48 g of sodium chloride in 0.459 L of water?

Answer 1

1)
mass % = mass of KI * 100 / mass of solution
8.58 = 10.0*100/mass of solution
mass of solution = 117 g

Answer: 117 g

2)

Molar mass of NaCl,
MM = 1*MM(Na) + 1*MM(Cl)
= 1*22.99 + 1*35.45
= 58.44 g/mol


mass(NaCl)= 4.48 g

use:
number of mol of NaCl,
n = mass of NaCl/molar mass of NaCl
=(4.48 g)/(58.44 g/mol)
= 7.666*10^-2 mol

Since density of water 1 Kg/L,
mass of water = 0.459 Kg

m(solvent)= 0.459 Kg

use:
Molality,
m = number of mol / mass of solvent in Kg
=(7.666*10^-2 mol)/(0.459 Kg)
= 0.167 molal
Answer: 0.167 molal