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