Question

Hydrochloric acid reacts with calcium to form hydrogen and calcium chloride. If 100grams of hydrochloric acid reacts with 100 grams of calcium, how much of the excess reagent will be left over after the reaction is complete?

Answer 1

Ca + 2HCl = CaCl₂ + H₂

n(Ca)=m(Ca)/M(Ca)
n(Ca)=100g/40g/mol=2.5mol

n(HCl)=m(HCl)/M(HCl)
n(HCl)=100g/36.5g/mol=2.740mol

Ca:HCl 1:2  ⇒  2.5:5!
calcium in excess

excess
Δn(Ca)=n(Ca)-n(HCl)/2
Δn(Ca)=2.5-2.740/2=1.13 mol
Δm(Ca)=Δn(Ca)·M(Ca)
Δm(Ca)=1.13mol·40g/mol=45.2 g