Chem Lab C

peoneill
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Re: Chem Lab C

Post by peoneill »

Hi guys! I'm running chemistry lab at state in Indiana this year and was a national medalist in 2002 when the topics were... chemical kinetics and aqueous solutions!!! Imagine that. These are actually great topics! And the calculations get quite tricky while staying fully within the rules if your event coordinator is clever enough (of course they should be asking the questions in a straightforward manner sometimes too, to get a good spread of where people should rank). I always thought titrations were a bit asinine; how much simpler can a lab activity be? The titration itself simply allows you to be exact with mixing two liquids.

Frankly, most lab equipment that event supervisors would be able to (or willing to) hand out to guests in their laboratory - especially young ones - won't allow them to grade your lab data to a super high level of precision, anyhow. I would imagine it was quite rare for a team at state to lose credit on titration itself. I've coordinated chemistry lab a handful of times and also because I like it I usually come check it out even when I'm coordinating a different event and I can tell you, it's pretty rare that the laboratory component really separates the medalists from the others at least at the state level.

Part of the problem is that it would be patently unfair to make you all guess what brand or the model and make of the specific lab equipment we're using. Therefore we have to instruct you on how to use it. Anyone with a cool head and a good mind for directions ought to be able to produce all of the data required for the event with plenty of time to spare - the other issue being if we try to jam it full of too many lab activities we're encouraging safety shortcuts or faking data or all sorts of unhealthy lab habits. So the lab component of chem lab can only be so difficult. I will say that a titration would be something that is so basic that it could be set up without giving you hardly any directions (just a few specifics on how that brand's nozzle works).

The real separation for the higher ranks tends to occur in writing about what is going on with the relevant chemistry in the lab and in the problem-solving portion of the event. You'll notice that the topics for chemistry lab coordinate fantastically well with the chapters of an intro college level (AP) textbook... They're probably based on some such textbook, in fact. The best preparation for chemistry lab is to A) have had chemistry and better yet AP Chem/Chem 2 in order to have had wide exposure to chemistry labs; B) figure out the 2 relevant AP chapters and study them; and C) predict the 2 or 3 labs that are most likely to appear at contest and get a chemistry teacher to set them up for you to go through once.
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Re: Chem Lab C

Post by peoneill »

@Tacooldude99: I do agree that the standard curriculum labs for aqueous solutions are pretty lame. Kinetics labs also tend to be imprecise and poor representations of how kinetics data is actually determined (too expensive/complicated for Olympiad!). From a lab perspective there are better topics for sure. But then again, like I said, the way this event works the problem-solving and writing about what's actually going on in the lab tends to be more important.

I wish I could tell you what I'm doing that I'm super excited about 8-) but I can't reveal my hand before the state tournament in Indiana. :cry: DOH!

PS Don't count out titrations. I did titrations ALL FOUR YEARS OF HIGH SCHOOL at my regional competition for topics varying from acid-base chemistry, thermochemistry, to (this year's very same) aqueous solution chemistry. All of these topics can be related to titrations (and were in Indiana from 1999-2002), which are a wildly popular topic with regional chemistry lab coordinators for whatever reason.
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Re: Chem Lab C

Post by scienceolympiadist »

Last year, you could count the lab portion to be about titration. This year, I'm not so sure. Anyone have broad ideas on the possibilities of the labs?
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Re: Chem Lab C

Post by Avia »

I know that this year covers kinetics and aqueous solutions. Do you think that equilibrium concepts will be incorporated into kinetics? As for aqueous solutions, the best lab would be a precipitate lab (mix mystery solutions and based off of the precipitate, guess the solutions) or a acidbase titration. What labs relate to kinetics? I know the basic mix different concentrations of reactants, find the initial rate and solve for the rate law, but that seems too complex for sci oly competition. I know that my state competition (RI) is very basic, like testtube/triple beam balance basic. Hope someone can reply.
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Re: Chem Lab C

Post by peoneill »

@scienceolympiadist: As I would point out, Avia's immediate interpretation of aqueous solution chemistry was that a titration would be one of the most appropriate labs, and I had such a titration as my lab activity for regionals with the same rules (nearly verbatim) for chemistry lab. I agree with your interpretation, a titration isn't really a great lab for these topics, but high school chemistry education has an obsession with titrations for some reason!

@Avia: Check the aqueous solution chemistry section closer. You might think that this means acid/base chemistry, as the chemistry of things dissolved in water (which is H+ with OH- after all) must be intimately related to acid-base chemistry... but read the details of the rules more closely! S.O. is using sort of a quirky definition of aqueous solution chemistry. First of all, they don't really mean AQUEOUS at all, as concentration, solubility, the colligative properties and Beer's Law are central topics and none of them are topics that apply to water specifically. Also, the qualitative analysis lab you've suggested for identifying unknowns through reactivity is technically chemistry occurring primarily between things dissolved in the aqueous phase, but is primarily chemistry about REACTIONS. The aqueous solutions topic essentially avoids chemical reactions entirely as written in the rules. It does NOT include acid-base chemistry or chemical reactions. In spite of this, both of the labs you have suggested are probable topics at regionals as hosting a guest laboratory is difficult and requires a great deal of preparation and both of these labs are relatively simple, easily set up en masse, and well understood to be appropriate for the high school level (and as most event coordinators are not professional educators their knowledge of high school appropriate labs is often minimal). Event coordinators may also be likely to make the same reading you did - using the title of the topic as their guide without closely examining the details of the how the topic is explained.

More appropriate labs for the aqueous solution chemistry topic would include:
[*]Determination of molar mass of a solute via freezing point depression or osmotic pressure (osmometer :D )
[*]Spectrophotometry
[*]Determining a solubility curve

etc. etc... These are listed explicitly in the rules for this year, in fact. I have many more ideas but I'm running chem lab at the Indiana State Tournament this year so I can't give out clues as to what topics I've thought up for the test beyond what is clearly stated in the rules.
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Re: Chem Lab C

Post by binary010101 »

Can someone explain Beer's Law?
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Re: Chem Lab C

Post by scienceolympiadist »

"relates the absorption of light to the properties of the material through which the light is traveling"
http://en.wikipedia.org/wiki/Beer%27s_law

looks confusing. I thought it was just a linear relationship between absorbency and concentration?
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Re: Chem Lab C

Post by peoneill »

Beer's Law is typically expressed as A=(e)bc only the (e) is actually the greek letter epsilon I can't type (either because there's no function for it or I'm just not smooth enough).

A = absorbance, which is a function related to the transmittance. Transmittance is how much light of a certain wavelength actually passes through the solution. Absorbance is a transformation of transmittance - the spectrophotometer does the math for you (even professionals don't usually know the details, spectrophotometers always present their results to you in terms of absorbance). Absorbance is more useful than transmittance because it has a LINEAR relationship to concentration, as you've noted.

(e) = molar absorbtivity coefficient (or constant), which is a constant that is different for each solution. This constant is the slope of the line in a typical Beer's Law plot.

b = the thickness of the path the light has to take passing through the solution... because most spectrophotometers always use a standard sized test tube (say the width is always 1cm for all measurements) this is essentially NOT a factor and can simply be omitted from the equation. Sometimes people call b "l" for length, but those people are lonely and should adopt a pet. Something affectionate, like a cat or a dog, not like a fish or a lizard.

c = the concentration of the solution; note that any units can be used so long as they are linearly based (i.e. you can't use pH or a logarithmic measure of concentration, but ppm, %, molarity, g/mL, etc. are all fine) AND so long as they MATCH THE UNITS OF (e). Normally you're just figuring out (e) for yourself so it's whatever units you feel like calculating it in. Typically real world chemists would be working in either ppm (for super dilute stuff, which is often what spectrophotometry is used for) or in M (molarity).

So yes, it's typically just linear, as A=(e)C meaning absorbance is directly proportional to concentration (remember (e) is just a constant, making it the slope of the line relating A to C). Also, Beer's Law graphs pass through the origin. My undergrads ALWAYS screw that up even after I warn them that they're going to. :x Bozos.
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Beer Law

Post by Avia »

I get what Beer's Law IS, but what kind of problems generally require the use of Beer's Law? Are they straight forward "Using Beer's Law, solve for this variable" or are they word problems or situation problems that require you to know intuitively that you need to use Beer's Law?
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Re: Chem Lab C

Post by zeebz -_- »

for Beer's Law,my team hd to determine what law it was and stuff like that. but,we didn't have a lab for that competetion and so all we had was the test.
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