Question

The lead storage batteries used in automobiles have a sulfuric acid (H2SO4) concentration of 3.75 M. The density of the sulfuric acid solution is 1.230 g/mL and the molar mass of sulfuric acid is 98.08 g/mol. What is molality of sulfuric acid?

Answer 1

M = 3.75 H"SO4

D = 1.23 g /ml

MW = 98.08 g/mol

a) Molality of H2SO4

molal = mol of acid / kg solvent

M = mol / Liter of solution

assume:

V = 1 Liter of solution

then we have 3.75 mol of H2SO4

mass of H2SO4 present in 1 L = 3.75*98.08 = 367.8 g of H2SO4 in 1 L of solution

find mass of solution

mass = D*V = 1.23 g/ml * 1000 ml = 1230 g of solutoin

since 367.8 g of that is acid then

1230-367.8 = 862.2 g of water

kg of water = 862.2/1000 = 0.8622 kg of water

then

molal = mol/kg = 3.75/0.8622 =4.3493 molal of H2SO4