[ChelseaRN]

HC2H3O2 is the formula of acetic acid. How many moles of carbon are in a 8.91 mole sample of acetic acid?
I have a bunch of questions like this on a computer drill that I'm doing for my summer course in Chemistry, and my professor did explain how to do some mole calculations but I don't understand how I would find out how many moles of just C there are in a sample of acetic acid.  The thing is I know the answer is 1.78E1 but I tried everything I could think of to get that answer but everything I try ends up different from that answer. please help me.
Chelsea

[savoy7]

a mole is a quantity - much like a dozen is a quantity
a dozen means 12 - a mole means 6.02E23

anyway if I have 8.91 moles of acetic acid and there is 2 C for every acetic acid

2 * 8.91 moles = 17.82 which is the same as 1.782E1 moles of C

[Ester]

a dozen means 12 - a mole means 6.02E23

Excellent way of comparing the two.
That is exactly how my professor taught the class about the concept of moles/Avogadro's number.