chemistry question?

Question

When 1.500 g of a metal oxide is heated, the compound decomposes in the reaction:

2X2O(s) ---> 4X(s) + O2(g)

If 0.1035 g O2 is produced, what is the identity of the unknown metal X?

Answer 1

Molecular mass of O2: 32.00g/mol
0.1035 g O2
<==> 0.1035/32.00 = 0.003234 (mole of O2 produced)
<==> 2*0.003234 = 0.006469 (mole of X2O to start with)
<==> 1.500/0.006469 = 231.9 (g/mol, as formula mass of X2O
<==> (231.9 - 16)/2 = 107.9 (g/mol, as atomic mass of X)
<==> X = silver.