Partial Pressures

[The Cancer Cure]

Hey guys,

 

Here is the question:

 

A mixture of gases contains 4.14 g of N2, 5.56 g of H2, and 7.06 g of NH3. If the total pressure of the mixture is 5.06 atm, what is the partial pressure of each component?

 

Find the partial pressures of N2, H2, and NH3.

 

Here is my attempt:

 

I took the grams of each one, and converted them into their moles via their grams divided by their molar masses. I added up their mole weights to get one large mole weight. I think took each individual mole weight and divided by the total mole weight. With this percentage, I multipled it by the total pressure, 5.06, to get their partial pressures.

 

What did I do wrong? - Because this isn't working.

 

Thanks guys.

[zule]

It would be advisable you write here what you have done in numbers. For example, how much do yo think the molar mass of N2 is?

[Fuzzwood]

Your method is valid, but maybe you are using the wrong molar masses.

[The Cancer Cure]

Okay, I wasn't sure if you minded if I wrote the numbers or not, but I will, sorry.

 

So:

 

Moles

 

4.14 g N2/28 g mol = 0.147857142857142 moles N2

 

5.56 g H2/2.0158 g mol = 2.75821013989483 moles H2

 

7.06 g NH3/17 g mol = 0.415294117647 moles NH3

 

Total Number of Moles = 3.321361400398972 moles

 

Mole Fractions

 

0.147857142857142 moles N2/3.321361400398972 moles = ~4.45%

 

2.75821013989483 moles H2/3.321361400398972 moles = ~83.04%

 

0.415294117647 moles NH3/3.321361400398972 moles = ~12.50%

 

Partial Pressures

 

.0445 * 5.06 atm = 0.22517 atm of N2

 

.8304 * 5.06 atm = 4.201824 atm of H2

 

.1250 * 5.06 atm = 0.6325 atm of NH3

 

Total atm = 5.059494 atm (Roundoff Error)

 

So...what am I doing wrong?

 

Sorry about not posting numbers earlier!

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Merged post follows:

Consecutive posts merged

Well, now I feel quite dumb.

 

My answers were correct, but I'm using WebAssign, and due to a 1% error because of roundoff error...my answer was incorrect. But since I worked it out again on here with multiple digits held, my answer was correct.

 

I had .224 atm N2 instead of the right answer - .225 atm N2.

 

Well, sorry, thanks for making me right it out though.

 

:doh:

 

Ignore this question, it is resolved.

[zule]

Why do you think you are doing something wrong? Because of the roundoff error? The roundoff error is logical , because you don't use all the possible decimals.

[The Cancer Cure]

Well, I didn't think I was doing something wrong...but I was getting the answer wrong - so then I thought I had done something wrong.

 

But then I found out it was a couple of decimals.

[zule]

Ok. I see you have post again while i was reading your previous post. So I see everything is right.

[The Cancer Cure]

Yep, thanks.