Na2SO4 is dissolved in water to make 450 mL of a 0.250 M solution. What is the molar mass of Na2SO4, and how many moles are needed?

Molarity is Given as,

Molarity = Moles / Volume of Solution - - - (1)

Data Given:

Molarity = 0.250 mol. L⁻¹

Volume = 450 mL = 0.45 L

Solving equation 1 for Moles,

Moles = Molarity * Volume

Putting values,

Moles = 0.250 mol. L⁻¹ * 0.45 L

Moles = 0.1125 mol

Now, converting moles into grams,

As,

Moles = Mass / M. mass

Or,

Mass = Moles * M. mass

Mass = 0.1125 mol * 142 g. mol⁻¹

Mass = 15.97 g

Result:

Molar Mass of Na₂SO₄ = 142 g. mol⁻¹

Moles needed = 0.1125 mol