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2011-11-26 14:20:14
Ryan
Member
+1,230|7060|Alberta, Canada

K, so I did a chem lab and I have to use my data to determine the value of the ideal gas constant, R.

This is my data:

R = PV/nT

P=0.8914atm (the pressure of the atmosphere minus the water pressure)
V=0.03999L (volume of water displaced)
n=1.4x10^-2 (I found the number of moles of NaNO2 and acid, then added them. Maybe this is where I went wrong?)
T= 292.7K (temperature of the water)

The reaction involved NaNO2 and sulfamic acid, which react to produce nitrogen gas and some other junk. We had to assume the temperature of the nitrogen was the same as the water, and the volume of nitrogen was the volume of the water displaced.

I get an R value of 0.008699079L atm / mol k. Shouldn't it be near 0.082057? Somethings wonky.
2011-11-26 14:21:25
presidentsheep
Back to the Fuhrer
+208|6178|Places 'n such
thought R was 8.31?

e: you did convert atm to Pa right?

e2: no, no you did not.

Last edited by presidentsheep (2011-11-26 14:24:10)

I'd type my pc specs out all fancy again but teh mods would remove it. Again.
2011-11-26 14:23:41
Ryan
Member
+1,230|7060|Alberta, Canada

presidentsheep wrote:

thought R was 8.31?

e: you did convert atm to Pa right?
We converted Pa into atmospheres. So basically if you use 8.314J/mol k and do unit conversions, you get 0.082057 L atm / mol k.

edit: I get 0.008699, but I should be around 0.08205, it's as if I have something to the wrong decimal place. My answer is like 8.6 times 10 to the negative 3, and it should be to the negative 2.

Last edited by Ryan (2011-11-26 14:25:58)

2011-11-26 14:26:57
presidentsheep
Back to the Fuhrer
+208|6178|Places 'n such
yeah, I reckon you've got the number of moles wrong then.
Dunno how you'd add stuff together, only a simple physics student here.
I'd type my pc specs out all fancy again but teh mods would remove it. Again.
2011-11-26 14:28:43
Ryan
Member
+1,230|7060|Alberta, Canada

presidentsheep wrote:

yeah, I reckon you've got the number of moles wrong then.
Dunno how you'd add stuff together, only a simple physics student here.
The lab manual said one mole of nitrogen is produced for each mole of NaNO2 and sulfamic acid used. So I calculated the number of moles of both, then added them together, and multiplied by a 1:1 mole ratio. I get 1.4x10^-2 mol of nitrogen.
2011-11-26 14:30:11
presidentsheep
Back to the Fuhrer
+208|6178|Places 'n such
1.4 moles would give a better answer? Maybe you've calculated one of the values for the stuff you're combining?
I'd type my pc specs out all fancy again but teh mods would remove it. Again.
2011-11-26 14:34:28
Ryan
Member
+1,230|7060|Alberta, Canada

If I rearrange PV = nRT for n and use the real value of R (0.082057), I should get 0.00148 mol of nitrogen.

My value: 1.4x10^-2 mol
Should have: 1.4x10^-3 mol

Agh I'm so close. Something is off by a decimal place. 39.99mL is 0.03999L right? lol
2011-11-26 15:20:25
(HUN)Rudebwoy
Member
+45|6972
Yes, the mL --> L conversion is right. Post the amount of reactants you used, maybe thats weher you've gone wrong.
On a sidenote: if you use atm instead of Pa, R should be 8.314/101325 = 8.2053*10^-5 since 1 atm = 101325 Pa
If you solve the equation for n with the above mentioned R, you get 1,48 mol.
Like I said: post your reactant specs.
2011-11-26 16:13:42
Ryan
Member
+1,230|7060|Alberta, Canada

K i gotta go to work, ill post back tomorrow morning with all the data.
2011-11-27 09:07:00
Ryan
Member
+1,230|7060|Alberta, Canada

I emailed my lab instructor and she said to use only the number of moles of sulfamic acid used. This number is equal to the number of moles of nitrogen gas produced.

So, I had 0.5586g of sulfamic acid, and that is equivalent to 8.65x10^-3 mol. Yet when I use this number in my equation, I get 0.02... something like that. This still isn't even close to 0.082057.

Something else must be wrong. Maybe I converted the pressures into atm incorrectly? Though I'm sure if you have mmHg, you just divide by 760 to get into atm.
2011-11-27 09:52:16
(HUN)Rudebwoy
Member
+45|6972
Yes 1 atm = 760 mmHg, but Im not sure how you could get 8.65*10^-3 mol.
molar mass of H3NSO3 is 97.1 g/mol, so n=5,7528*10^-3 mol

The only thing left is that you read the pressure wrong. What kind of device did you use for measuring pressure? Digital barometer, manometer, etc? What did it look like?(I assume you didn't read the displacement of water wrong )
2011-11-27 10:18:38
Jay
Bork! Bork! Bork!
+2,006|5575|London, England
Chemistry 101 is hard
"Ah, you miserable creatures! You who think that you are so great! You who judge humanity to be so small! You who wish to reform everything! Why don't you reform yourselves? That task would be sufficient enough."
-Frederick Bastiat
2011-11-27 10:21:01
Hurricane2k9
Pendulous Sweaty Balls
+1,538|5919|College Park, MD
so
https://static.bf2s.com/files/user/36793/marylandsig.jpg
2011-11-27 10:25:54
Ryan
Member
+1,230|7060|Alberta, Canada

(HUN)Rudebwoy wrote:

Yes 1 atm = 760 mmHg, but Im not sure how you could get 8.65*10^-3 mol.
molar mass of H3NSO3 is 97.1 g/mol, so n=5,7528*10^-3 mol

The only thing left is that you read the pressure wrong. What kind of device did you use for measuring pressure? Digital barometer, manometer, etc? What did it look like?(I assume you didn't read the displacement of water wrong )
I was looking at the wrong number. My number of moles of acid was what you stated above. My bad.

We didn't really use an instrument for measuring the pressure. We took to the atmospheric pressure (as read from a barometer, on that day it was 695mmHg) and subtracted the vapor pressure of the water at it's temperature (the water I was using remained pretty constant at around 20 degrees C, so the corresponding pressure was 0.02308atm.

So 695mmHg equals 0.9145atm, minus 0.02308atm gives me a pressure reading of 0.8914atm for the pressure of the nitrogen gas.
Temperature of the N2 gas was assumed to be equal to the water temp, so 292.7K. Volume of gas produced equals volume of the water displaced in the buret, so 39.99mL (0.03999L). And my intructor said to use n=5.7528x10^-3 for my value of n.

It still doesn't give me a proper value for R.
2011-11-27 10:28:14
(HUN)Rudebwoy
Member
+45|6972
Well by far the data are all over the place, Im just trying to interpret
2011-11-27 10:32:40
Ryan
Member
+1,230|7060|Alberta, Canada

I GOT IT. Fuck sakes!

Stupid mistake! The number of moles of sulfamic acid equals the number of moles of nitrogen gas. But we divided the acid into 4 trials, 25mL each. So I have to divide the moles of sulfamic acid by 4.

When I do that, I get 0.08467, which is pretty darn close to 0.082057

Wowzas.

edit: Which is only a 3.2% difference, and the allowable is 5%. Thank God.

Last edited by Ryan (2011-11-27 10:33:47)

2011-11-27 10:38:57
Jay
Bork! Bork! Bork!
+2,006|5575|London, England

Ryan wrote:

I GOT IT. Fuck sakes!

Stupid mistake! The number of moles of sulfamic acid equals the number of moles of nitrogen gas. But we divided the acid into 4 trials, 25mL each. So I have to divide the moles of sulfamic acid by 4.

When I do that, I get 0.08467, which is pretty darn close to 0.082057

Wowzas.

edit: Which is only a 3.2% difference, and the allowable is 5%. Thank God.
What degree are you chasing? Looks like first year of engineering to me...
"Ah, you miserable creatures! You who think that you are so great! You who judge humanity to be so small! You who wish to reform everything! Why don't you reform yourselves? That task would be sufficient enough."
-Frederick Bastiat
2011-11-27 10:44:47
Ryan
Member
+1,230|7060|Alberta, Canada

Jay wrote:

Ryan wrote:

I GOT IT. Fuck sakes!

Stupid mistake! The number of moles of sulfamic acid equals the number of moles of nitrogen gas. But we divided the acid into 4 trials, 25mL each. So I have to divide the moles of sulfamic acid by 4.

When I do that, I get 0.08467, which is pretty darn close to 0.082057

Wowzas.

edit: Which is only a 3.2% difference, and the allowable is 5%. Thank God.
What degree are you chasing? Looks like first year of engineering to me...
Bachelor of Science majoring in geophysics, possibly just geology if I don't like the geophysics aspect of it.
I'm loving chemistry this year though. So much interesting stuff to learn. I was gunna do chemical engineering, but the horror stories about engineering scared me away. Sounds super difficult.
2011-11-27 10:46:39
Pochsy
Artifice of Eternity
+702|5760|Toronto

Jay wrote:

Ryan wrote:

I GOT IT. Fuck sakes!

Stupid mistake! The number of moles of sulfamic acid equals the number of moles of nitrogen gas. But we divided the acid into 4 trials, 25mL each. So I have to divide the moles of sulfamic acid by 4.

When I do that, I get 0.08467, which is pretty darn close to 0.082057

Wowzas.

edit: Which is only a 3.2% difference, and the allowable is 5%. Thank God.
What degree are you chasing? Looks like first year of engineering to me...
Yes Jay, once again your degree was super hard and you are the smartest cat around.

Take it easy on that crap, Jay. Maybe Ryan finds this stuff difficult; no reason to berate the guy to make yourself feel better.
The shape of an eye in front of the ocean, digging for stones and throwing them against its window pane. Take it down dreamer, take it down deep. - Other Families
2011-11-27 10:49:05
(HUN)Rudebwoy
Member
+45|6972

Ryan wrote:

But we divided the acid into 4 trials, 25mL each. So I have to divide the moles of sulfamic acid by 4.
facepalm

Glad you got it.
2011-11-27 10:49:28
Jay
Bork! Bork! Bork!
+2,006|5575|London, England

Ryan wrote:

Jay wrote:

Ryan wrote:

I GOT IT. Fuck sakes!

Stupid mistake! The number of moles of sulfamic acid equals the number of moles of nitrogen gas. But we divided the acid into 4 trials, 25mL each. So I have to divide the moles of sulfamic acid by 4.

When I do that, I get 0.08467, which is pretty darn close to 0.082057

Wowzas.

edit: Which is only a 3.2% difference, and the allowable is 5%. Thank God.
What degree are you chasing? Looks like first year of engineering to me...
Bachelor of Science majoring in geophysics, possibly just geology if I don't like the geophysics aspect of it.
I'm loving chemistry this year though. So much interesting stuff to learn. I was gunna do chemical engineering, but the horror stories about engineering scared me away. Sounds super difficult.
It is, but it's worth it. Geology is good if you want to work for an oil company testing samples all day but there isn't much else you can do with it. Chemical and Petroleum engineering are the two highest paying bachelor's degrees if that factors into your decision at all. First year of a science degree is fun, just don't kill yourself on the chem lab reports. In the grand scheme of things you're obsessing over inconsequential stuff Chemistry is largely a dead subject, so have fun with it

Last edited by Jay (2011-11-27 10:51:48)

"Ah, you miserable creatures! You who think that you are so great! You who judge humanity to be so small! You who wish to reform everything! Why don't you reform yourselves? That task would be sufficient enough."
-Frederick Bastiat
2011-11-27 10:51:15
Jay
Bork! Bork! Bork!
+2,006|5575|London, England

Pochsy wrote:

Jay wrote:

Ryan wrote:

I GOT IT. Fuck sakes!

Stupid mistake! The number of moles of sulfamic acid equals the number of moles of nitrogen gas. But we divided the acid into 4 trials, 25mL each. So I have to divide the moles of sulfamic acid by 4.

When I do that, I get 0.08467, which is pretty darn close to 0.082057

Wowzas.

edit: Which is only a 3.2% difference, and the allowable is 5%. Thank God.
What degree are you chasing? Looks like first year of engineering to me...
Yes Jay, once again your degree was super hard and you are the smartest cat around.

Take it easy on that crap, Jay. Maybe Ryan finds this stuff difficult; no reason to berate the guy to make yourself feel better.
In what way was I berating the guy? I was simply asking him what his path was. Between his Newtonian physics questions, and his inorganic chemistry questions, it looked like the first year of an engineering or science degree.

What a silly thing to attack me for.

Last edited by Jay (2011-11-27 10:52:54)

"Ah, you miserable creatures! You who think that you are so great! You who judge humanity to be so small! You who wish to reform everything! Why don't you reform yourselves? That task would be sufficient enough."
-Frederick Bastiat
2011-11-27 10:53:02
(HUN)Rudebwoy
Member
+45|6972

Jay wrote:

Chemistry is largely a dead subject, so have fun with it
Wut?

Forget it, Im not gonna get sucked into the political vortex of BF2s
2011-11-27 10:54:34
Ryan
Member
+1,230|7060|Alberta, Canada

And I don't find it difficult. I'm probably sitting at an 80 or an 85 in the class, but when it comes to the labs, nothing seems to ever work out the way it should.

And yea, I plan on working for an oil company, probing underground for reservoirs and such. But there is alot more you can do with a geophysics major as well, but working for an oil company seems the most probable. Up in northern Alberta, oil is huge up there.
2011-11-27 10:55:39
Jay
Bork! Bork! Bork!
+2,006|5575|London, England

(HUN)Rudebwoy wrote:

Jay wrote:

Chemistry is largely a dead subject, so have fun with it
Wut?

Forget it, Im not gonna get sucked into the political vortex of BF2s
No no, it's not political at all. Chemistry is just a subject where there aren't really any new frontiers. They have nice models and constants and the compounds are known. Organic chemistry, yes, is still open due to biochemistry, but inorganic is a rather dead end subject that was superceded by physics. That's all I meant.
"Ah, you miserable creatures! You who think that you are so great! You who judge humanity to be so small! You who wish to reform everything! Why don't you reform yourselves? That task would be sufficient enough."
-Frederick Bastiat

 

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