Question

a particular sample of zinc-aluminum alloy weighs 3.00 g and has mass percentages of 73.5% Zn and 26.5% Al.
a. how many moles of each element is in the alloy sample?
b. how many theoretical moles of H2 (g) will be produced by the reaction of HCl aq with each metal and what will be the total number of moles produced?

Answer 1

a)
mass of Zn = 73.5 % of 3.00 g
= 2.205 g
moles of Zn = mass/molar mass
= 2.205/65.38
=0.0337 mol

mass of Al = 3.00 - 2.205 =0.795 g

moles of Al = mass of Al/molar mass of Al
= 0.795/26.98
=0.0295 mol

b)
Al + 3HCl ---> AlCl3 + 1.5 H2
Zn + 2HCl ---> ZnCl2 + 1 H2

moles of H2 produced = 1.5*mol of Al + 1*mol of Zn
= 1.5*0.0295 + 1*0.0337
= 0.0779 mol
mass of H2 = number of moles of H2 * molar mass of H2
= 0.0779*2
= 0.156 g
Answer: 0.156 g H2 is produced