Homework Help: Gas stoichoiometry

1. Sep 27, 2008

magma_saber

1. The problem statement, all variables and given/known data
A compound has the empirical formula CHCl. A 256 mL flask, at 373 K and 750. torr, contains 0.800 g of the gaseous compound. Give the molecular formula.

2. Relevant equations
Only equation i know that relates to this is PV=nRT.

3. The attempt at a solution
I have absolutely no idea.

2. Sep 27, 2008

Redbelly98

Staff Emeritus
That's the right equation. Plug in all the numbers you can into it, and see what happens.

3. Sep 28, 2008

magma_saber

All that will give me is "n." what good does that do?

4. Sep 28, 2008

Staff: Mentor

n and 0.8 g - combine these two numbers.

5. Sep 28, 2008

magma_saber

how does that give me the molecular formula? i'm still lost...

6. Sep 28, 2008

Redbelly98

Staff Emeritus
The empirical formula is CHCl. Given that, what are the possible molecular formulas?

7. Sep 28, 2008

Staff: Mentor

Check what it does give you. Very important property of substance.

8. Sep 28, 2008

magma_saber

By this do you mean add n and 0.8? If so then i get 0.808. now what?

9. Sep 29, 2008

Staff: Mentor

No, I didn't told you have to add them. Look at the units - one is number of moles, second is grams. You can't add them just like that.

There is a very important property of each reagent that combines moles and grams, and is extensively used in all almost chemical calculations. Seems to me like you have calculated that 0.008 mole is 0.8 g. Can you calculate now mass of other number of moles of the same substance?