What mass of manganese (II) chloride must react with sulfuric acid to release 48.5 mL of hydrogen chloride gas at STP? MnCl2 (s) + H2SO4 (aq) →MnSO4 (aq) + 2HCl (g)

Note that one mole of any gas at STP occupies 22.4 L of volume. We may use this to calculate the moles of hydrogen chloride gas that need to be produced. This is:

0.0485 / 22.4

0.002 mol

Next, we see that the molar ratio between manganese chloride and hydrogen chloride in the equation is:

1 : 2

So the moles of manganese chloride reacting will be:

0.002 / 2 = 0.001 mol

The molecular mass of manganese chloride is 126 g/mol. The mass reacting will be:

0.001 * 126

0.126 grams of manganese (II) chloride will react.