Avogadro’s number

Question

I am taking a combined bio+A&P course and the whole molecules and atoms mess is confusing, but I’m getting it. But I can’t wrap my head around Avogadro’s number. Please help?

Edit: Thank you everyone! This was a huge help!!

In: 23

Answer 1

Its just a way to convert mass to number of atoms/molecules and vice versa.

If you have a chemical reaction of, for example, burning carbon C + O2 -> CO2, then you understand reaction by counting atoms in formula, one carbon atom to two oxygen atoms, easy. But if you are handling reagents, you are measuring them by mass, so you need to convert somehow.

Avagadros number of things is one mole of things. One mole of carbon atoms is 12 grams of carbon because carbon has a mass number of 12, 6 protons, and 6 neutrons.

So let’s say you are burning 12 grams of carbon. How much oxygen do you need for complete combustion?

Well, as per formula, one mole of oxygen molecules or two moles of oxygen atoms, same-same. How much is it in mass? Oxygen has 8 protons, 8 neutrons, and mass number 16, so one mole of oxygen atoms is 16 grams. You need two moles, so 32 grams of oxygen are needed.