Question

Given the following balanced equation, calculate the theoretical yield of H2 in grams if you start with 25.3g Zn and have an excess of HCl. Zn(s) + 2HCl(aq) → ZnCl2 (aq) + H2

Answer 1

The theoretical yield of H₂ in grams is =

calculation

Zn(s) + 2HCl(aq) → ZnCl₂(aq) +H₂

Step 1: find the moles Zn

moles = mass÷ molar mass

from periodic table the molar mass of Zn = 65.4 g/mol

moles is therefore = 25.3 g/65.4 g/mol=0.387 moles

Step 2: use the mole ratio to determine the moles of H₂

from given equation Zn:H₂ = 1:1 therefore the moles of H₂ is also =0.387 moles

Step 3: find theoretical mass of H₂

mass= moles× molar mass

from periodic table the molar mass of H₂ = 1 × 2 = 2 g/mol

mass =0.387 moles × 2 g/mol =0.774 grams