Question

A 2.25 gram sample of zinc metal reacts with 5.00 grams of hydrochloric acid to give zinc chloride and hydrogen gas according the blanced equation:

Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g) Molar mass ZnCl2: 136.28 g/mol

a. What is the limiting reactant?

b. What mass of ZnCl2 can be formed? (This is called the theoretical yield.)

Answer 1

Number of moles of Zn = 2.25 g / 65.38 g/mol = 0.0344 mole

Number of moles of HCl = 5.00g / 36.46 g/mol = 0.137 mole

from the balanced equation we can say that

1 mole of Zn requires 2 mole of HCl so

0.0344 mole of Zn will require 0.0688 mole of HCl

but we have 0.137 mole of HCl which is in excess so

Zn is the limiting reactant

1 mole of Zn produces 1 mole of ZnCl2 so

0.0344 mole of Zn will produce 0.0344 mole of ZnCl2

1 mole of ZnCl2 = 136.28g

0.0344 mole of ZnCl2 = 4.69 g

Therefore, the theoreticale yield of ZnCl22 = 4.69g