the acid was phosphoric acid and apparently, the first equivalence point was super hard to identify
@racecar45 It should be fine to discuss now. My section sent out question booklets to students/teachers in the mail today.
@bmebois I started with 10 mL of acid. First equivalence point after adding ~10 mL NaOH, second after adding an additional ~10 mL NaOH. So, I was pretty sure the solutions were equimolar. I added ~15 mL more NaOH and there was no significant color change.
I really wonder what we missed.
@ParadoxChem126 The thing is, I think I remember the H2SO4 being added to the precipitate, not the filtrate… whatever, tests are supposed to be returned tomorrow.
I still don’t understand how the reaction order was two. I did three trials, and got 1.91 = 2^n ==> 2 = n.
my local section coordinator said it was 1 in iodide (and he gets the answer keys)
^idk, I got 2 in iodide, and our coordinator said that was right 
Also, if you just google ‘ACS flame test safety’, apparently the right answer was using a wooden splint and no methanol 
ya using methanol is hella dumb (how to kill people 101)
Anyone remember the Cyanide and Nickel compelx question?? The answer had to be either 1.00 or 4.15 (or 4.65) or something. Anyone know the answer??
@huhululu I am pretty sure it was 1.00. The formation constant is so large that you never get enough hydrogen ion in the solution. Mainly a conceptual question if my reasoning is right.
@1golfer1 you are probably right for the PH one. I picked 4.65 because i knew the pH had to be lower than the original HCN. I figured 1.00 was too unreasonable so i picked 4.65 when I was running out of time. Anyone remember if one of their answers were BaCO3?
for the antimarkovnikov addition, was the correct answer because of the radical intermediates?
Exposure to light would encourage free radical additions, which would put the bromine on the unsubstituted carbon.
Realistically, what do you think the cutoff is? Around 40 maybe? Or is that too low. I don’t want to be too optimistic here lol
@ParadoxChem126 I would expect the multiple choice cutoff to be, at a maximum, 45.
id think it be high 40’s because this test wasn’t too hard and competition has been getting a lot harder
Does anybody remember all four options for the flame test question? I can’t remember the difference between the two options for wooden splints.
a. squirting from a meter away
b. holding a bunsen burner over a ceramic plate filled with the soln.
c. soaking the wooden splint and holding it in a bunsen burner
d. I think this one was put the wooden splint on a hot plate or something but i really can’t remember
a is how you kill yourself
The acid in the lab can’t be phosphoric because the third equivalence point (and the third half way point) are above pH 11 and our ratchet af indicator only goes up to 10
My graph had a jump in pH from below 4 to 5.5 between two measurements and then a leveling off and then another jump all the way to pH 10 and above so I said diprotic with the two large jumps being the two eq points. If there was another eq. point above 10 or below 4, there was no way to find it b/c there was only one level (buffered) portion of the graph.
http://bau7.pt/wp-admin/maint/phosphoric-acid-titration-with-sodium-hydroxide-i7.gif
That’s the phosphoric acid titration curve above btw
@snuffles168 LOL “ratchet af indicator,” but absolutely true. It is impossible to detect the third equivalence point directly with the indicator we were given. I am wondering if USNCO wanted us to add Fe(III) to the unknown acid and observe its effect on the system.
Practically everyone in my section got these answers:
- First Order in Fe(III)
- Zeroth Order in Iodine
- Diprotic
it was definitely triprotic. i personally got diprotic and i know all of the other students in the lab got diprotic, but the coordinator specifically said it was triprotic, and i don’t think he’ll lie lol