summer school

[lucas marcone]

never fail chemistry! do what you must but relearning chemistry alone is not an easy task. infact i had to look through the phone book for my teacher. it's rough man.

[Zedd]

Heh you too? Im still looking for an old teacher of mine

[xHaZxMaTx]

Oi, I hated my chemistry class.   But Physics was awesome!

I just finished summer school today - had to make up my Government class that I failed.  Now that I'm done with that, I'll be graduating, tomorrow.

[lucas marcone]

lucky punk....well i hope you make some snide remark to them about the extra hassle

[lucas marcone]

anyone take AP chemistry?

i was talking with my teacher on the phone today.....guess what? i was takeing basic chemistry but when i failed that the school hands me a text book of advanced placement chemistry! this means i not only have to relearn what i did in my base line class (dumbed down further for vo-tech kids) but i also have to learn the smart peoples chemistry.


HOW IS THIS FAIR?!?

[llearch n'n'daCorna]

Who said life is fair?

[bill]

Maybe you shouldn't have failed chemistry.

[lucas marcone]

yeah yeah my fault. but im being serious now. can anyone here help me with AP chemistry?

[superluser]

yeah yeah my fault. but im being serious now. can anyone here help me with AP chemistry?

Been a while since I studied it, but I can probably help with the stuff up through basic orgo.

[lucas marcone]

O.K. What do you know about raiseing boiling points and lowering freezing points?

[nikename2]

My memory is hazy but I believe it has to do with surrounding pressure? Thats why your blood boils in outer space if your unprotected because there is no pressure or something......yea...

[DarkAudit]

This link has the answer, at least as far as adding salt to the water is concerned.

[superluser]

O.K. What do you know about raiseing boiling points and lowering freezing points?

Xeksue is right.  The phase change points are determined by a function of temperature and pressure.  Look up phase diagram in your text.

Basically, it's a gas until the pressure is high enough and the temperature is low enough.  Then, (depending on the substance) it can become a liquid or a solid, but you're probably dealing with things that become liquids.  Again, when the pressure is high enough and the temperature is low enough, it can become a solid.

As I mentioned earlier, there are some substances that can go straight from solid to gas, because they cannot exist as liquids under our atmospheric pressure.  Carbon dioxide is one of these.  Look up the phase diagram for CO2.  Do you see why this is?

As for changing freezing/boiling point with something in solution, BillDarkAudit has it right, though a clearer explanation may be found here.  Essentially, the solvent (usually water) has to push out the solute (often salt) before it can leave the liquid phase.  The more solute, the greater the change to boiling/freezing points (in fact, it is directly proportional to the molality (not molarity)--that is, moles of solute per kilogram of solvent (not solution)).

If they're talking about latent heat, I can tell you a bit about that, as well.

[lucas marcone]

thank you so much! i have the idea down but there is appearntly a formula in finding out how to determine these temp.s and the book assumes you know alot more about it than i already do so it never comes out to tell you how.

[Brunhidden]

Specialization is for insects.

[superluser]

thank you so much! i have the idea down but there is appearntly a formula in finding out how to determine these temp.s and the book assumes you know alot more about it than i already do so it never comes out to tell you how.

It's in the link:

http://www.nyu.edu/classes/tuckerman/honors.chem/lectures/lecture_13/node8.html

ΔT_f = K_f * m

T_f is the temperature at the freezing point.  I don't know how far you've gotten in math, but delta (Δ) T_f is amount that the freezing point changes.  K_f is a constant for whatever solvent you're using, and m is the molality.

Since it's a direct linear relationship, you can figure out some problems without even having all the information.  For example--

A 1 molal solution of water and a solute freezes at -.51 degrees Celsius.  At what temperature will a 2 molal solution freeze? (I omitted a very critical number--pun not intended--but you should know this number already)

[lucas marcone]

this may sound like a stupid question but how do i convert grams to moles again?

i only know up to algebraII ....i think i know for sure i took algebraI

[superluser]

this may sound like a stupid question but how do i convert grams to moles again?

Oh, geez--this won;t be easy to explain.  It depends on what you're measuring.  A mole is (let's see if I can remember it) 6.022*10^23 of anything.

It's quite useful when you realize that one mole of a substance will weigh the same number of grams as a single unit will weigh in AMUs.

OK.  Let's try that in English.  You have one carbon atom.  Look up its atomic weight on the periodic table.  It should say something like 12.011.  12.011 is how much one average carbon atom weighs in atomic mass units (AMUs).  That doesn't help, because that sort of weight is impractical or impossible to measure.

But we can measure in grams, and we know that if you have 12.011 grams of carbon, you have 6.022*10^23 carbon atoms.  So we gave that number a special name, the mole.  Here's an equation that may be able to help:

gram =  mol * amu

If I gave you 24.022 grams of carbon, how many moles of carbon did I give you?  What about 24 grams of hydrogen?

[lucas marcone]

so to find the mol. it's


   grams= Amu*X where X is moles


   so G = AmuX
       ----------------         = X       
          Amu                         

in other words moles is equal to grams devided by Amu?

[superluser]

   so G = AmuX
       ----------------         = X       
          Amu                         

in other words moles is equal to grams devided by Amu?

I'm not sure if I'm following your equation, but your explanation is correct.

By the way, I'm sorry I brought AMUs up.  It's unlikely that you'll need to know about them unless your chemistry teacher mentions it.  Just remember that if you need to know how much a mole of something weighs, just add `grams' to the end of the atomic weight.

[lucas marcone]

i set it up like an algebraeic equation to find X  AMU * X + AMUX then devided... thanks alot now i can keep truckin. though im going to call the hotline about sending me an ap chem when i failed basic... though they'll probably say "screw you complete it or fail..."

[bill]

Is taking the actual AP test a pre-req for passing the course?

[lucas marcone]

well let's say i would have gotten my science credit for just takeing basic chemistry.....

[superluser]

Is taking the actual AP test a pre-req for passing the course?

I have no clue what it's like at lucas' school, but typically, the AP test is optional.  The grade that you get on the AP test doesn't impact at all on the grade for the course, just on whether or not the credit will transfer for college.

[lucas marcone]

at my school there are two corses.....basic and AP
AP to my understanding has nothing to do with the transfer of credits.....just it's a much higher diffaculty.


basic is just the basic into to chemistry