How many liters of a 2.25 molar hydrobromic acid (HBr) solution would be needed to react completely with 100.0 grams of calcium metal?

Ca (s) + 2HBr (aq) CaBr2 (aq) + H2 (g)

We can solve by dimensional analysis. We are already given with the concentration of the acid, the amount of the metal, and the balanced chemical reaction, so:

100 g Ca (1 mol Ca / 40 g Ca) (2 mol HBr / 1 mol Ca) (1 L HBr / 2.25 mol HBr)

= 2.22 L HBr

It would require 2.22 L of HBr to react completely 100 g of Ca.