[TFD]

Here is the first question I can't seem to figure out:

How many moles of ammonium ions are in 0.621 g of ammonium carbonate?

The second i keep getting the answer of: C8H20Pb, but I'm told that is wrong. Here's the question:

What is the empirical formula of the following substance?
tetraethyllead, the "lead" in gasoline: 29.71% C, 64.06% Pb, 6.23% H

[enahs]

Question 1, what is the formula? How many mols of that compound do you have?

Second one, why do you have oxygen in your compound. Where was it given?
You have to convert the weight percents into mols.

[Borek]

Second one, why do you have oxygen in your compound. Where was it given?

It is not oxygen, it is C₈H₂₀Pb. And this is a correct answer (at least in terms of number of atoms in the molecule). Could be they want elements in formula in other order.