Getting Empirical Forumula Using Ideal Gas Laws

[Lancelot59]

Homework Statement

C_xH_y gets burned in oxygen gas and makes CO₂ and water. Given the partial pressure of water and the total pressure of the resulting mixture I need to find the empirical formula.

Homework Equations

Well PV=nRT is the obvious choice...but all the information you see there is all that's given. The only other thing I was able to find was the pressure of the CO₂ just doing some subtraction. The problem doesn't state a volume, temperature or anything else.

Can I assume that temperature is a constant and eliminate it? How about volume? I'm not sure about that, if I can then it might help.

 

[symbolipoint]

The problem description is far too general. You must have some known given conditions.

 

[Lancelot59]

Nope that's it. All we know is that a hydrocarbon was burned, and the pressure of the products. We can't assume standard conditions because the pressure is off.

There's another problem I couldn't solve:

A mixture of the gases CO and CH3COCH3 (acetone) is trapped in a 1.0 L flask. The pressure in
the flask registers 100 mmHg initially but the pressure registers 114 mmHg after the acetone in the
flask is caused to decompose according to the following reaction at the same temperature:
CH3COCH3(g) H C2H4(g) + CO(g) + H2(g)
If all the substances present are in the gas phase, and CO is unchanged by any chemical reaction,
what were the inital and final pressures of CO, assuming complete reaction of the acetone?

Again, how can I proceed? I don't think enough is known.

 

[Bohrok]

Nope that's it. All we know is that a hydrocarbon was burned, and the pressure of the products.

Well you didn't include the pressure in your posting.

 

[Lancelot59]

Oops...

The total pressure of the mixture is 1.2 atm and the pressure of the H2O is .686 atm. That still doesn't help much...does it?

 

[Borek]

Yes it does - it gives you partial pressure of CO₂, and that means you know exact molar ratio of H₂O and CO₂.

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methods

 

[Lancelot59]

Actually it's just carbon monoxide. So that means everything in the decomposition is 1:1. I'll canker around with it and see where I can get. Dalton's pressure law seems a reasonable place to start.

 

[Borek]

Sorry, misread the question - but it doesn't matter much, it is still molar ratio that counts.

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methods