Empirical formula for a compound question..please help...?

Question

A 9.54g sample of a compound containing only copper and oxygen was converted into copper by a reduction process involving hydrogen gas. The mass of the copper that remained after the reaction was 7.62g.
Determine
a) the empirical formula for the compound
b) if the relative formula mass of the substance is 79.55, what is its true formula and its proper name?

Note: Please help me answer these questions...I can't work out either a or b. Please explain the steps and processes involved if possible. Please be 100% certain of your answers and show working. Thanks

Answer 1

If the sample only contains copper and oxygen, the lost mass from the original sample must be from oxygen.

So, there are 7.62 grams of copper and 1.92 grams of oxygen. The 7.62 grams of copper equals 0.120 moles of copper (MW Cu = 63.546), while the 1.92 grams of oxygen is 0.120 moles of oxygen (MW O = 15.9994 [note do not use O2 in this calculation). The ratio of the two moles being 1:1, the empirical formula is CuO.

CuO's molar mass is 79.55, so the empirical formula is the molecular formula. The proper name is either copper (II) oxide or cupric oxide (older nomenclature).

Answer 2

Thanks for thrushing me into the world of chemistry, though I've only studied chemestry for about 4 minutes I figured out a molecular formula is 6 times the emperical formula. Did you already know that alot? Ok, maybe not 6 times but I now know the word mole and part of why chemistry is confusing. when there's a lil number on the bottom left of a number (or variable) of a chemical it's technically miltiplied by the chemical, but when I did math that little number meant there were two variables but had the same letter, why not just put the number behind the sucker with parenthesis, maybe science would be easier if not purposly made confusing.