Question

Molarity of H2SO4 is 18 M. It's density is 1.8g/cm^{​​​​​3}, hence molality is?

Answer 1

Remember : 1ml=1cm3
molality = mol $H_{2}SO{}_4$ /kg solvent
molarity = mol $H_{2}SO{}_4$ /L solution

Using density,
Mass of the solution = 1.8g/ml * 1000 ml = 1800g

Molecular weight of $H_{2}SO{}_4$ = 98g

Mass of solute ($H_{2}SO{}_4$) = 18 mol * 98 g = 1764 g

Mass of solvent = mass of solution - mass of solute
= 1800 g - 1764 g
= 36 g = 0.036 kg

Molality = mol $H_{2}SO{}_4$ / kg of solvent
= 18 mol/0.036kg
= 500 mol/kg