Empirical Formula Problem

[Joseph Fisher 2K]

I was working on this practice problem:

"A 7.00 g sample containing only lead, carbon, and hydrogen was burned in an oxygen‐rich environment. The products of the combustion were 6.841 g CO2(g) and 3.97 g H2O(g). What is the empirical formula of the compound?"

I started solving this problem by converting the CO2 and H2O into moles. I also was able to isolate the mass of C and H in grams. But, now I'm confused as to how I should account for the oxygen while still finding the empirical formula for C, H, and Pb. Please let me know what I should do next.

[Evonne Xu 3I]

If you have already been able to isolate the mass of C and H in grams then there is no need to account for oxygen at this point since the sample only contains carbon, hydrogen, and lead. Simply subtract those masses from the sample's total mass of 7.0g to get the mass of Pb, and then convert them to moles and work from there to find the empirical formula.