Gamoc
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Post by Gamoc on May 9, 2008 21:59:16 GMT -5
This subject is really starting to annoy the crap out of me. I start getting something and my teacher throws something new at us.
Does anybody else like/hate this subject?
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~CrAzY~™
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Post by ~CrAzY~™ on May 10, 2008 0:36:30 GMT -5
I'm an ace in Chemistry. For some reason, EVERYTHING has clicked just right in my brain. Well, it's of course more difficult now near the end of the year, but I'll still manage to pull off a high A.
What part are you guys on right now? Past stoichiometry yet?
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carnageX
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Post by carnageX on May 10, 2008 3:23:55 GMT -5
We just got done with stoichiometry. Managed to pull off a 90% on it (only got 4 wrong heh). It's not my best subject, but I'm decent at it. It can take em a little while to learn how to do something, but once I learn/do a few things involving it, I know how to do it usually. Funny...cuz about 3/4 of the kids in my Junior class that took Chem, didn't know wth they were doing on this test and literally guessed on every question...lol.
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Gamoc
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Post by Gamoc on May 10, 2008 6:55:27 GMT -5
We are WAY passed stoichiometry. We are on finding pressure, volume, and things like that. I'm finally starting to get it...and then she keeps throwing new things at me and I just don't get it. Half of these problems don't even look like they have enough information, or are given a unit of measure that I can't find out how to change into one that will work for the problem.
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~CrAzY~™
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Post by ~CrAzY~™ on May 10, 2008 17:18:58 GMT -5
It seems like you're working with gas laws, and that is immediately after stoichiometry for us.
Are you talking about PV=nRT?
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Gamoc
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Post by Gamoc on May 10, 2008 19:46:38 GMT -5
It has to deal with that, yes...but it's gotten really weird. Now we're getting stuff in grams per mol...and I'm not sure how to work with that.
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~CrAzY~™
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Post by ~CrAzY~™ on May 11, 2008 2:56:57 GMT -5
I'm not 100%, but I would guess you take grams per mol and figure out what element it is? Not sure if we've covered that just yet. (We're on gas laws though)
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Gamoc
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Post by Gamoc on May 11, 2008 6:29:41 GMT -5
Well, I know what element it is...it's given to us. I just really don't know what to do with it.
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~CrAzY~™
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Post by ~CrAzY~™ on May 11, 2008 13:07:50 GMT -5
You could always give an example of the problem(s) you're working on as an example.
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Gamoc
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Post by Gamoc on May 11, 2008 16:31:20 GMT -5
Well
N2 = 28.02 g/mol
What is the density of n2 measured at STP?
I don't get it. We haven't talked about density at all (although I'm sure it has a lot to do with pressure) and haven't used g/mol at all.
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Post by generations on May 11, 2008 17:45:54 GMT -5
I remember chemistry from eighth grade. I kind of liked it.
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~CrAzY~™
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Post by ~CrAzY~™ on May 11, 2008 18:30:14 GMT -5
Density = Mass/Volume. STP = Standard Temperature & Pressure (0oC & 1atm)
You have mass, you need volume. You convert the mass to mols, plug it into PV=nRT with 273okelvin and 1atm for the P. Formula: Volume(L)=(moles of element)(.0821 L·atm·K-1·mol-1)(273oK) / 1atm.
Convert this to mL (milliliter) so that it works with the grams measurement in the density equation (tiny and giant just doesn't match here). Plug it in and divide. The answer could be said as g/mL or (more commonly) g/cm3 because they are equivalent.
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Gamoc
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Post by Gamoc on May 12, 2008 16:10:06 GMT -5
Actually, no. I found out how to work the problem today. I was supposed to divide 28.02 by 22.4 and there was my answer.
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~CrAzY~™
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Post by ~CrAzY~™ on May 12, 2008 21:02:50 GMT -5
Actually, yes. You get 22.4 by SOLVING the equation I showed. It's really expanded, so I guess it's hard to see.
1 atm on the bottom cancels out, leaving 22.4 x Moles of element on top. Since you're working with 1 mole of N2, it doesn't do anything so you don't need it (multiplying/dividing by 1).
That means the volume is 22.4L.
D=M/V, aka: 28.02/22.4
Memorizing certain numbers is often a good thing, but what if it was 1.5atm? Then you would be thrown off completely and get the wrong answer unless you know the connection between 22.4 and PV=nRT.
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Gamoc
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Post by Gamoc on May 12, 2008 21:23:27 GMT -5
Oh, well that part of it wasn't explained to me, there. I was just told that was how to do it.
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~CrAzY~™
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Post by ~CrAzY~™ on May 12, 2008 21:31:45 GMT -5
I see your teacher prefers to tell you only how to get the answer to the questions, as opposed to actually teaching the methods.
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carnageX
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Post by carnageX on May 13, 2008 0:11:33 GMT -5
22.4 is a constant though, so I'm assuming he was given it as a constant in his textbook, to use to solve the equation. I know that we're usually given the STP (if not, we know its 22.4 when we're solving things).
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Gamoc
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Post by Gamoc on May 13, 2008 16:50:02 GMT -5
Our teacher gave it to us, our textbook is so stupid (and the teacher knows it, too).
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~CrAzY~™
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Post by ~CrAzY~™ on May 13, 2008 19:06:06 GMT -5
STP isn't actually 22.4. STP is 0oC and 1atm (standard temperature and pressure) and can be used in any equation involving temperature and pressure. Well, I guess if you're only needing STP in that one problem type, it works if you memorize the number, but that's terrible practice.
My teacher's logic: Chemistry isn't about your ability to remember a number. If it was, then why does every chemist have a big reference book with all the constants and specific values? In order to be a good in chemistry, you need to know how things connect and the methods used to solve problems.
On our gas laws test this Thursday, he will be supplying constants (R) and a periodic table for us to use. Does that mean the class will ace it? No, far from it. In fact, I'm one of only a handful in his 2 chemistry classes that will get an A. This is because his tests are designed to see if we learned it, not just memorized it.
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Gamoc
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Post by Gamoc on May 13, 2008 22:07:18 GMT -5
I knew what STP was, she just gave us that number. Well, I have a Gas Law test and a bunch of work to do with it tomorrow. I've been busy all night, so I'll be rushing throughout the whole day to get it done.
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~CrAzY~™
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Post by ~CrAzY~™ on May 14, 2008 3:01:24 GMT -5
I knew what STP was, she just gave us that number. Well, I have a Gas Law test and a bunch of work to do with it tomorrow. I've been busy all night, so I'll be rushing throughout the whole day to get it done. Finishing homework the day of a test, talk about pressure. ;D [/corny chemistry joke]
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Gamoc
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Post by Gamoc on May 14, 2008 5:59:50 GMT -5
Yeah, I have quite a bit, unfortunately. The volume of the papers is very large. [/even cornier chemistry joke]
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