Official Ap Chemistry Fr Discussion

tm2000 · 05-12-2005, 03:10 PM

Here it is! Let's talk

tm2000 · 05-12-2005, 03:24 PM

Ok well on number 1, i don't remember my answers. However, I know methanoic acid was stronger.

I did number 3: Here's a BIG question I have here. For the value of the rate constant, i put 610. I know, when you test the 1 reaction, you get about 611.7. HOWEVER, because of sig figs, i put 610, since the concentrations only had 2 sig figs. I also tested the other reaction, and got answers in the 610'2. SO i don't know, hoefully I'll get credit.
Ln(h2o2) was the answer for the graph, seconds to the minus one, and I THINK the line should be drawn above the first (a slope not as steep).

OK, for 4. Here's what I did:
Zn + Ni2+ --- Zn2+ + Ni
Al(OH)3 + OH- ---- Al(OH)4 -
C2H2 + O2 --- H2O + CO2
Li + N2 --- Li3N
Pb2+ + I- === PbI2

I know everyone is right except the aluminum one (complex ion), although im pretty sure its right.

For 5, i missed the splint one, but diff reactions are supposed to occur.
CaO will be basic, SiO2 neutral, CO2 acidic (H2CO3)
Ag2S is black, 1/3 AgCl will precipitate, sol 1 is Ag NO3, 2 is Na2S, 3 is KC;.

6: C with for bonds to each F
P with five bonds to Fs
S with four bonds to F and one pair of elctrons
bond anlge is 109.5
sp3d for pf5
and seesaw for sf4
4 sigmas, 1 pi
structrue 1 is best (no formal charge)

7: NH3 is hydrogen bonding, NF3 is DIPOLE DIPOLE, difference cuz hydrogen bonding is stronger than dipole
KCl and NaCl is ionic bonding,
NaCl is stronger cuz closer atomic radii

quantum level is 3, shielding is the reason for ion. energies, cuz theres a stronger nuclear pull on the outer electrons as one goes right across periodic table

Cu is element, (for what reason, i said cuz the isotopes weights seem like to average to CU's weight)
62.93 is more abundant cuz of the weighted average concept, it's weight is closer to Cu's weight.

Ok, so that's what i did!

tm2000 · 05-12-2005, 03:25 PM

o, if i said ''atomic weight'' instead of ''mass,'' will i be counted against? i wasn't sure which to use.

primitivefuture · 05-12-2005, 03:28 PM

Did anyone get CH4O as the emperical formula?

Flame tests:
1. NO2 - Flame is turned down. Sometimes there is brown fumes coming out.
2.H2 - Small combustion with a "pop" sound
3.O2- flame rekindles.

HELTAHIR · 05-12-2005, 03:28 PM

tm2000, you are supposed to say atomic weight. Use atomic weight, because you are compiling a weighted average of the different weights. I didn't get that SiO2 would be neutral, I said acidic.

Also, if anyone did question 2, did you get the empirical formula to be C2H2O5, and that the acidity of 2.6 pH was due to a carboxyl group?

primitivefuture · 05-12-2005, 03:29 PM

I got 2.6 as the pH too.

HELTAHIR · 05-12-2005, 03:32 PM

What? What are you talking about primitivefuture? The problem already said the pH was 2.6. It asked you what functional group was responsible for this. I said carboxyl group, and got C2H2Of as empirical.

berry986 · 05-12-2005, 03:33 PM

Heltahir, I got pH 2.6 too and the carboxyl group

tm2000 · 05-12-2005, 03:45 PM

SiO2 is netural, cuz SiO2 has network covalent bonding, it's IMFs are too strong and won't react with water's hydrogen bonds.

http://www.chemguide.co.uk/inorganic/group4/oxides.html

"Silicon dioxide doesn't react with water, because of the difficulty of breaking up the giant covalent structure. "

madskier87 · 05-12-2005, 03:47 PM

Its kinda funny that they would give you a combustion reaction for one of the written formulas. Its a free 2 points if you know one of the most basic concepts of chemistry. I also got 2.6 for the pH and put the exact same answer as primitivefuture, minus that it turns brown when exposed to nitrogen. I believe you are correct though. TM2000 I think they might take off a point if you don't mention shielding on 7. Hoping for a 3

homie · 05-12-2005, 03:51 PM

other reactions were:
CaCO3 + HC2H3O2 >>> Ca2+ + C2H3O2- + H2O + CO2

BF3 + NH3 >>> F3B:NH3

SO3 + OH- >>> HSO4-

madskier87 · 05-12-2005, 03:51 PM

o yeah, I have another question. What were the units on the straight line graph one? I put log(concentration). I also drew a straight line from the starting point, but it had a less steep slope.

greygoo · 05-12-2005, 03:54 PM

I also did the log of concentration. for the graph I actually plotted out all the points

homie · 05-12-2005, 03:56 PM

i think it was natural log ( ln [H2O2] ) because it says the reaction was first order

tm2000 · 05-12-2005, 04:03 PM

umm, i don't think shielding is right. I was looking at answer keys for past FRs very similiar to this, and some actually say shielding is not a correct response. Cl is a common ion for both, so it doesn't matter.