<p>more specifically, only the decimals are sig in pH. pH=3.32 has 2 sig figs</p>
<p>I’m sorry, I shouldn’t have said decimal places, that was dumb. What I meant to say was I got an answer like 3.27 - will that stand if the answer is 3.32 etc. ?</p>
<p>950 K was indeed the answer. Yes!</p>
<p>Generally, accumulated rounding errors aren’t much of a problem, but in the pH calculation, most of the intermediate numbers were round numbers, so it’s hard to see how you would get 3.27 without making a mistake somewhere. Do you remember your intermediate work?</p>
<p>No, I don’t… I’ll have to re-work the problem…</p>
<p><em>Sigh</em> And I now I redid the entire problem and got 3.32 - therefore, I must be senile, and I must be remembering my answer incorrectly. AP addles your brains… :)</p>
<p>For the K=1 one, when K=1 it is at equilibrium…at that point dG becomes 0 so just subsitute into dG = dH - TdS</p>
<p>0= dH -TdS</p>
<p>solve</p>
<p>i got in the 940s i dont remember if it was 949 but i’m sure it was</p>
<p>AHHHHH I see. Delta G from part a was specifically for 298 K…why did I plug that in? Who knows. At least people I talked to made the same mistake, so Im not a total idiot.</p>
<p>Oh. I just did the acid problem over… and it ends up that I DID get it right (3.32 pH). This is how I did it:</p>
<p>.006 mols F- created during neutralization / 40 mL = .15M F-
.004 excess HF / 40 mL = .10M HF</p>
<p>7.2E-4 = [.15]x/[.10]
x= 4.8E-4
-log(4.8E-4) = 3.32</p>
<p>Which is basically the same thing as the Henderson-Hasselbach eq… but I got confused. =P Ha, ha.</p>
<p>you know 5MV questions … were we supposed to actually write out 5MV ?
cause i just wrote … you multiply MV to get moles and use coefficient ratio, multiply by five … somethin like that … i didnt actually wrote out 5MV or for next two qs … but i explained how to find grams using Molar mass and percent ratio etc… do u think they will still give me pts ??</p>
<p>Ahh nooooo… for 6 f), I think I put the ratio gets smaller… but I said that the reaction shift left. Wasn’t thinking X_X so I’d get 1 point right?</p>
<p>what did you guys get for the equations</p>
<p>First, I had a precipitation… I forget what the reactants were, though. One was Pb, I think?
Then a standard acid-base reaction (H2O, Ca2+, and CO2 as products)…
Finally, I had an oxidation/reduction reaction (Ag+ + Fe2+ –> Ag(s) + Fe3+)</p>
<p>"cause i just wrote … you multiply MV to get moles and use coefficient ratio, multiply by five … "
Yeah… I did that, too.
I think I wrote:</p>
<p>MV x 5 moles Fe ion/1 mol MnO4- = moles Fe ions</p>
<p>Also, for the color change one… I struggled a LOT. I remembered slightly from a lab that we did a year ago that the colors involved were clear/purple. But, I also knew that Fe3+ is yellow-brown in solution. So, I said that it went from purple to yellow. Obviously, I was wrong… but why doesn’t the color of Fe3+ have an effect? Is it just overwhelmed…?</p>
<p>thats what i got too LesOs =)
first one was … Pb(OH)2
so u dont think they are gonna take off pts for not writing exactly 5MV ??</p>
<p>i had:</p>
<p>2OH- Pb2+ –> Pb(OH)2</p>
<p>2HNO3 + CaCO3 –> H2CO3 + Ca2+ + 2NO3-</p>
<p>Ag+ + Fe2+ –> Ag + Fe3+</p>
<p>not positive about the middle one, but pretty certain about the first and last</p>
<p><a href=“College Board - SAT, AP, College Search and Admission Tools”>College Board - SAT, AP, College Search and Admission Tools;
the test is there FYI</p>
<p>for the questions for reactions did you guys get acid rain and silver?</p>
<p>I think I screwed up the middle one too 
</p>
<p>Yeah acid rain erodes the CaCO3 and solid silver metal.</p>
<p>i got 3 moles products, acid rain, and Ag :D</p>
<p>i think it was 1/2 mol</p>