# Homework Help: Simple Mole Conversions

1. Nov 22, 2008

### jacksonpeeble

What is the mass of methane (CH4) if it occupies 32.3 L at STP?

We got a whole bunch of these problems on a worksheet with minimal instruction. If somebody could please aid me in solving this one, then I should be able to solve the rest.

I assume that I must first find the masses of the individual components...

C = 12.0107 * 1 = 12.0107
+H = 1.00794 * 4 = 4.03176
---------------------------
16.0483

Then I honestly don't know what to do... I don't want the answer; I'd just really appreciate if somebody could show me how to do this. I tried searching for a guide online, but none of them really had what I was looking for.

Thank you!

2. Nov 22, 2008

### symbolipoint

STP means Standard Temperature and Pressure.
Use PV=nRT.

3. Nov 23, 2008

### Staff: Mentor

Which - sadly - doesn't mean anything.

jacksonpeeble: you have to know what temperature and pressure your teacher want's you to use as STP, as this thing is not precisly defined.

4. Nov 23, 2008

### jacksonpeeble

1 mole = 22.4 L at STP according to my teacher.

What do I do with that equation? I assume that it is the same as (Pressure x Volume)/(Temperature x Moles) = R, but how is this applied?

Thanks for the help so far, though!

5. Nov 23, 2008

### fayeshin

and then let 32.3 L = x mol at STP. you can get x. do you know how to do now? (forget that equation...for this problem, it is useless.)

6. Nov 23, 2008

### Staff: Mentor

How many moles of methane then?

What is molar mass of methane?

While PV=NRT is the general method, that will give exactly the same results if applied correctly, you can solve the question using just the information quoted above.

7. Nov 23, 2008

### jacksonpeeble

Ah, so it's essentially just a ratio?

So it would be 32.3/22.4 = 1.44 Moles?

8. Nov 24, 2008

### Staff: Mentor

Now moles to mass and you are ready.

Note, that if you will be given exact pressure and/or temperature value you will have to use PV=nRT equation.