Question

To prepare 1 g of hydrogen molecules using hydrochloric acid how many grams of zinc should be taken?

Zn +2HCl ------>ZnCl2 + H2

Answer 1

Zn +2HCl ------>ZnCl2 + H2

from reaction it is clear that,
1mol of Zn react to form 1 mol of hydrogen.

atomic mass of Zn = 65.38 g
atomic mass of H2 = 2 g

that is,
65.38 g Zn react to form 2g hydrogen.

.˙. For 1g hydrogen, Zn neeeded = 65.38/2 = 32.69 g

Zn should taken = 32.69 g