Question

A student begins with 125 mL of a Na2SO4 solution and evaporates the water from the mixture. The resulting material has a mass of 19.83 g.  What is the concentration (M) of the original solution?

(calculate answers to 2 decimal places)

Answer 1

molar mass of $Na_2SO_4$ = 142 g/mol

mass of $Na_2SO_4$ in the solution = 19.83 g

number of moles of $Na_2SO_4$ = $\dfrac{19.83}{142}$ = 0.14 mol

Volume of solution = 125 mL = 0.125 L

molarity (molar concentration) =$\dfrac{\text{number of moles}}{\text{volume of solution}}$ = $\dfrac{0.14}{0.125}$ = 1.12 M$.$