chem help please? =D?

Question

copper (II) oxide is reduced by hydrogen to copper and water:

CuO + H2 ---> Cu + H2O

What mass of copper(II) oxide will be reduced by excess hydrogen to give 16g of copper.

do i need to do:

mass = moles x molar mass?

thanks

Answer 1

16 g Cu = 0.252 moles Cu (16.0 g / 63.54 g/mole)
0.252 moles of CuO will give 0.252 moles of Cu
0.252 moles CuO x 79.54 g/mole = 20 g CuO

Answer 2

CuO + H2= Cu + H2O
the molar ratios are 1:1::1:1
Moles (Cu) = 16g/64 = 0.25 moles
As the molar ratios are all 1:1
Moles(CuO) = 0.25
Mr (CuO) = 64 + 16 = 80
mass/g = 0.25x80 = 20g - the answer!!!!

Yes. your do need to use mass = moles x molar mass.