# Calculate the number of molecules of O2 when given the number of moles

1. Dec 16, 2017

### axer

1. The problem statement, all variables and given/known data
After balancing an equation, there are 1.82 moles of O2.

Calculate the number of molecules of O2. given moles.
2. Relevant equations

3. The attempt at a solution
in every O2 molecule, there are 2 moles of O.
so if the number of moles of O2 molecule is 1.82. then 1.82*2= 3.65 moles.

number of molecules= 3.65*6.022*10^23= 2.19*10^24.
Correct?

2. Dec 16, 2017

### Staff: Mentor

In every single molecule?
That is the number of oxygen atoms. The question asked about the number of O2 molecules.

3. Dec 16, 2017

### axer

Oh.. so the number of molecules is just no. of moles times molar mass?
no need to multiply by 2?

4. Dec 16, 2017

### Staff: Mentor

Number of moles times molar mass is a sample mass.

Think about a mole as of an overgrown dozen, with 6.02×1023 objects instead of 12. You have two dozens of molecules - how many molecules? You have two moles of molecules - how many molecules?

5. Dec 16, 2017

### axer

2*6.02×1023

the question included no of moles

6. Dec 16, 2017

### Staff: Mentor

Right.

7. Dec 17, 2017

### epenguin

Maybe you have go the question confused with the other possible similar kind of questions.
Forget everything you know about oxygen - it's irrelevant here.
Calculate the number of molecules of anything in 1.82 moles of that thing.
Is the same for anything.

8. Dec 17, 2017

### Staff: Mentor

Beware: part of the OP answer was plainly wrong.