Question

How many grams of ZnO would you need to produce 50 g of ZnCl2? (The atomic mass of Zn is 65.38 and of Cl is 35.45.)

ZnO(s) + 2HCl(aq) → ZnCl2 (s) + H2O(l)


17.1 g
29.8 g
59.7 g
83.8 g

Answer 1

ZnO(s) + 2HCl(aq) → ZnCl2 (s) + H2O(l)

Look at the moles:

1 + 2 → 1 + 1

How much ZnO do we need to make 50g of ZnCl2? Notice it is these numbers in () and should be 1:1

(1) + 2 → (1) + 1

So we need the same number of moles, but how many moles is 50g of ZnCl2? Zn weight is 65.38g, and Cl is 35.45g. So ZnCl2 is (65.38) + (2 X 35.45)=136.28g

50g/136.28g = 0.3669 moles

What is 0.3669 moles of ZnO now?

O weighs 16g/mol, so add 65.38 + 16 = 81.38

Multiply by 0.3669 moles and get how many grams we need.