# Homework Help: Converting Mol

1. Nov 14, 2007

### Renzokuken

[SOLVED] Converting Mol

1. A 20-cm-diameter cylinder that is 40 cm long contains 50 g of oxygen gas at 20 degrees celsius.

How many moles of oxygen are in the cylinder?

so 1 mol = 6.022*10^23
oxygen atomic mass=16g/mol
50g/16(g/mol) = 3.125 mol

I don't know why it is wrong, someone told me it is 50g/32(g/mol) but why is it 32 instead of 16?

2. Nov 14, 2007

### symbolipoint

Do you mean 50 grams of oxygen gas, or do you mean of oxygen by mass as if all were present counted as the atoms?

You then basically have V, T, you might need R (look for the value in a book);
Actually, the number of moles will not change. You said you have "50 grams", but you did not say as the atoms or as the diatomic gas. You only need to know 1 mole equals 6.02*10^23 units. You need to know if you were given just mass of oxygen atoms or mass of diatomic oxygen.

3. Nov 14, 2007

### Renzokuken

ok i get it, i didnt see the gas part. It was talking about O2 thanks