Molarity/molality help #7

Question

Determine the number of grams of solute needed to make each of the following molal solutions.

(a) a 4.54 m solution of H₂SO₄ in 1.05 kg H₂O

__ g

(b) a 1.19 m solution of HNO₃ in 2.01 kg H₂O

__ g

Answer 1

a). 4.54 m H2SO4 means 4.54 moles H2SO4 per kg H2O

Since you want to use 1.05 kg H2O, we need 1.05 kg x 4.54 mol / kg = 4.77 mols H2SO4

molar mass H2SO4 = 98.1 g/mol

g H2SO4 = 4.77 mols x 98.1 g = 468 g H2SO4

b). 1.19 m HNO3 means 1.19 moles HNO3 per kg H2O

Since you want to use 2.01 kg H2O, we need 2.01 kg x 1.19 mol / kg = 2.39 mols HNO3

molar mass HNO3 = 63.0 g / mol

g HNO3 = 2.39 mols x 63.0 g / mol = 151 g HNO3