Question

combustion of 0.356g of an unknown metal sample in oxygen gives 0.452g of an oxide in the form of mO2, Identify the unknown metal?

Answer 1

I think I would approach it this way.
.....M + O2 ==> MO2
...0.356g.......0.452
So you know oxygen = 0.452-0.356 = 0.096 g

Then I would calculate percent.
M = (0.356/0.452)*100 = 78.76%
O2 = (0.096/0.452)*100 = 21.24%

Take a 100 g sample which gives us
78.76g M
21.24 g oxygen.

Convert to moles.
moles M = 78.76/molar mass = ??
moles O = 21.24/16 = 1.3275.
We know moles M must be 1/2 of 1.3275 = ??
Then 79.76/molar mass = 1/2*1.3275 and solve for molar mass.