Calculate the mass

Question

Calculate the mass of manganese sulfate monohydrate , MnSO4·H2O, required to make 25 mL of a 0.020 M solution.

Answer 1

Molar mass of MnSO4·H2O = 151 + 18 = 169 g/mol

0.020 M = 0.020 moles/liter

Since we only need to make 25 ml (0.025 L), we only need...

0.025 L x 0.020 mol/L = 0.000500 moles of MnSO4·H2O

mass needed = 0.000500 moles x 169 g/mol = 0.0845 g = 0.085 g MnSO4·H2O needed (2 sig. figs.)