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10-20-2004 05:20 PM  13 years agoPost 1
NitroSpazzz

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I need a lil help on my chem lab thats due thursday. It was a simple titration lab. We crushed up aspirin tablets (3 samples approx same weight) and then dissolved the aspirin in water (rougly 100 ml but it doesn't matter). Then we very slowly dripped NaOH (Sodium Hydroxide) into the stuff until we saw the color change and stay. So once the pink color (from the indicator) stays the moles of NaOH are approx at a 1:1 ratio to the acid in the Aspirin. What I need to do is figure out how many grams of this Acetylsalicylic Acid was in our sample.

I think what I need to do is take the mL of NaOH used, convert to moles. Then from there since 1mol NaOH=1mol Acetylsalicylic Acid I convert the moles of Acetylsalicylic Acid into grams of Acetylsalicylic Acid. Only problem is I am not completely sure how to do it. Kind of stumped. I know its not a very difficult thing but its really hanging me up right now.

Thanks

Blake

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10-20-2004 05:29 PM  13 years agoPost 2
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You're on the right track....

For find the moles of NaOH used, take the Molarity (mols/liter) times the # of liters, this will give you moles used.

Then since you have that and they're a 1:1 ratio, you have moles of Acetylsylic acid. Take the number of moles and times it by the molecular weight (grams per moles) and then you'll have grams of Acetylsylic acid.

So you'll need the molarity of your NaOH, #of liters used to complete the tritration, and the molecular weight of Acetylsylic acid. If you dont' have the last one, you may find it on Chem Exper.

Out of curiousity, is this gen chem or organic? And if it's organic are you using the electron flow theory??

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10-20-2004 05:45 PM  13 years agoPost 3
NitroSpazzz

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Thanks for the help. I have the molarity of the NaOH its .109M I just forgot to mention that. This is general chemistry so we are just doing real basic stuff. Plus I won't be taking organic (from what I have heard I don't want to take it) because I am doing the mechanical option of Composite Material Engineering I can't wait till physics I love that stuff.

Blake

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10-20-2004 06:10 PM  13 years agoPost 4
Blair

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Hi Nitro,

Interesting post and a nice diversion from the regular stuff on here.

What level chemistry is that? High School? University?

Blair

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10-20-2004 06:18 PM  13 years agoPost 5
NitroSpazzz

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University Chem at Winona State University (Minnesota)

WAY Aside from topic...anyone fly around winona? I miss my helis

Blake

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10-20-2004 08:56 PM  13 years agoPost 6
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If you're doing anything chemistry related (as materials science definately is), I'd suggest taking Organic. Couple of reasons, one being that it gives you a good perspective on other types of chemistry, you'll be lost without if you're working with anything more the simple organic molecules. And if you don't have good study habits, it will force you to get them. Either that or you won't do well.

I personally liked it, although it was hard and ate up a significant portion of my time during the semester, but then I knew that going in. And since I was thinking of being a chem major I took it. Well worth it in my opinion. Besides, it's never a bad thing to have more knowledge than what's required.

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10-21-2004 05:07 PM  13 years agoPost 7
NitroSpazzz

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Good point on that organic. I have a question for you...I followed what you said and I end up with more Acetylsalicylic acid that I did aspirin.

Take for example this test:
- 30.88mL NaOH used....03088L NaOH (.109M)
- Mass of crushed aspirin tablet=.327 grams

So .109M=x/.03088 x=.00336592 moles NaOH
Molecular Weight Acetylsalicylic Acid (C9H8O4)=180.16

So 180.16 x .00336592=.606404g of Acetylsalicylic acid in a .327g tablet of aspirin?

How is this happening? I have got to be missing a very important step somewhere?

Blake

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10-21-2004 06:50 PM  13 years agoPost 8
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It all works, first you have .03088liter X .109 Moles/liter, so the liters cancel and you're left with .0036592 moles NaOH. Then Acetylsalicylic acid is 180.16 grams / mole X .0036592 moles. Moles cancel and you have .606 grams of Acetylsalicylic acid. The dimensional analysis works fine.

All your calculations check out. I would guess the problem is either in the weight of the samples, or the amount of NaOH used.

You sure it's just .327 grams for the tablet? And did you stop the titration when it just held the pink color, or did you go until it was a dark pink? Did you clean the glassware before starting the experiment? How much NaOH did other people in your lab end up using, is it inline with yours? What's different between your measurements? Did the balance get zeroed properly? Bunch of things could happen to affect it, just a matter of finding out what and how.

To get an idea, look on the label of the bottle from the aspirin. They'll usually have a listing of the percentage of active ingredients, or the milligrams that each tablet has. This will give you an idea of where you should be. For instance if it's 500mg per tab, you probably used just a little too much NaOH.

Sorry about the problems, I really hate when that happens.

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10-21-2004 07:04 PM  13 years agoPost 9
NitroSpazzz

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So what should I do then? I have three tests, all of which are about the same mass and used pretty close to the same amount of NaOH. I guess I'll just do a big write up of how we messed up on something whether it was cleaning the stuff or whatever. We titrated until the pink color stayed but was very light.

Blake

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10-21-2004 07:12 PM  13 years agoPost 10
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I'd definately check with other people in the class and see if they had the same sort of problems. Also double check to see what the mass of their tabs were. Scratch that, compare all your figures to theirs. If you're all using the same tabs it should be really close, so just see where yours are off and see if that explains the problem.

On more than one occasion I've had problems with chemicals in the lab. Either they've been labled wrong, or they weren't mixed or stored correctly. I've been as close as .09% error on a titration and also been as high as 95% error. That's the fun of chem lab, numbers don't lie so it's finding the problem elsewhere.

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10-21-2004 07:12 PM  13 years agoPost 11
Brian Bennett

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No problem from what I see. Physics-nut has you on the right path.

There many other congeners and additives present in an aspirin tablet, cellulose, caffeine heroine ect. Most all is sold as a "buffered" formula which consist of the acid and its conjugate base salt. This make tummies less upset. The number crunching looks fine.

moles of NaOH used = moles of acid present in sample
why? There is one carboxyllic acid proton for every one molecule of aspirin in its acid form.

just double check your standardization numbers of the NaOH titrant as a final check.

Brian

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10-21-2004 07:23 PM  13 years agoPost 12
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I assume you took Organic. Did you take the version based off of electron flow analysis? I ask cause my professor wrote a book on it, and always went on about how only a few schools do it this way. So I'm curious if really only a few school do it that way or it it's standard.

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10-21-2004 07:45 PM  13 years agoPost 13
WMac

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While we're on the subject, you can help me with my homework. Is the systematic name for CBrClFI (that's a capital i) bromochlorofluoroiodomethane?

Will


Beep Beep! One Road Travel, with Dominic Byrne!

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10-21-2004 07:56 PM  13 years agoPost 14
dariof

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Where do you braniacs come from.

I thought law school was difficult. Gee, with these studies you're doing, I would have never made it.

Best Regards, Dario

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10-21-2004 07:58 PM  13 years agoPost 15
Brian Bennett

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WMAC,

If you mean IUPAC system, you are correct: its a Methane derivative with substituents in aphabetical order. It should also fall under some funny freon naming system also.

DARIO - it pays the bills, but its painful

Brian

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10-21-2004 08:03 PM  13 years agoPost 16
dariof

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Brian:

Seriously..my hat's off to you people.

I know there are many very important applications to everyday life created from the type of work you do. Almost everything we use has a basis in chemistry/physics.

I simply am not smart enough..so I went into aviation (flew for United) then law. Have always been fascinated by the sciences however..maybe next lifetime.

Best Regards, Dario

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10-21-2004 09:59 PM  13 years agoPost 17
WMac

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Cheers BB, I guess it is the IUPAC system, not covered any freony type stuff yet

Will


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10-21-2004 10:31 PM  13 years agoPost 18
NitroSpazzz

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Well I figured out why everything was off. He molarity of the NaOH was PURPOSELY not told to us. He wanted to see what would happen. So once everything was all turned in he asked everyone what they used for molarity. Everyone used the .109 from the previous lab. He proceeded to tell us it had a molarity around .05 So that ticks me off a lil bit, everyone is loosing points for it. I did however mention that the only way for our calculations to be anywhere near what they should be was to have a molarity of around .054 or something. But anyways thats for the help everyone. I am sure there will be many more labs I am not sure of.

Blake

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10-21-2004 10:47 PM  13 years agoPost 19
DeadFox

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boo!!

I did however mention that the only way for our calculations to be anywhere near what they should be was to have a molarity of around .054 or something.
Oooo!! Booo!! Hisss!! dirty trick! You should have gotten partial credit for bringing that up tho..

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10-21-2004 11:03 PM  13 years agoPost 20
NitroSpazzz

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I guess thats what we get for assuming though. We should have known better than that. Just got out of lab class and this weeks lab was pretty simple. So no questions for you guys this week.

Blake

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