@sonpat - It’s a buffer problem. When you add HCl, a strong acid, the pH doesn’t change, so something must consume the H+. Cl- has a negligible effect on the pH because it’s the conjugate base of a strong acid; therefore, only the H+ affects it. You can eliminate B right away because of this.
The species in your solution are H+, C2H3O2- (from the HC2H3O2) and C2H3O2- (from the NaC2H3O2).
H+ = H3O+. It’ll donate its extra proton by reacting with an anion, C2H3O2- in this case.
I’m cramming for the upcoming test and have some questions:
Where as reaction 1 features in increase in entropy due to phase change, reaction 2 also features an increase of entropy because there are more gas molecules
@rhubarbb the second reaction. More moles of gas = more volume = more positions for the gas molecules = more disorder
Need some help on 2014 MC,
8, I sort of get the math pathway and I ended with the right answer, but I still don’t understand exactly why and how to do it.
17, I don’t understand at all
20, does pKw directly correlate to pH?
21, just a general question, the only time that Kc can change is from changes in temperature correct?
23, I thought it would be exactly 2.4
30, narrowed down to D/A, don’t understand the rest
39, no clue
40, dont understand why
Thanks for any help!
https://www.youtube.com/watch?v=eYa_xpzxToE I found this channel’s videos to be very helpful for acid/base and he also has others and https://www.youtube.com/watch?v=HoEBBIkKHc0 is a pretty good overview
Can someone explain when to recognize that it’s a k=x^2/a problem
What are the answers to 42 and 47? Never really learned about solids in my class! Thanks 
Check the ap chemistry exam on collegeboard it says the frq is split into calc and no calc
@rhubarbb I think since it’s measuring increase in entropy both double the amount of moles of gas, so we have to consider the phase change, making reaction one have a greater increase in entropy, as it’s going from a solid and a gas to two gas, doubling gas and having a phase change, while the second is going from 2 moles of gas to 4 moles of has, doubling gas, but without the phase change.
@apactstudent So it’s always the number of gas molecules in the products, essentially?
@stemscholar This makes sense. It’s all relative, then, yes? Even though reaction 2 has more gas products, the one with the greatest delta S will be reaction 1?
^Sometimes it could depend on a phase change, for example, solid–>liquid and liquid–>gas both involve and increase in entropy.
@rhubarbb Yes. You can think of it like that, but only for gaseous molecules
@shiftydraw I don’t have the 2014 MC test but for 21, yes Kc only changes if temperature changes. Also Kw=[H][OH] so kind of for 20
Hey guys, I got a 5 two times on practice AP chemistry exams. Which are the 2014 exam and 2013. I would highly recommend you guys to score a 45/50 multiple choice and at least a 30/50 on FRQ. The total score would be a 75 and that would definitely be a 5 on the AP. The scoring distribution changes every year so we dont know the score to get a 5 so its better to aim for that composite score in order to guarantee a 5 for sure.
@rhubarbb I’m pretty sure yes, also it may make sense to consider that halving all of the reactants in the second equation will give you essentially the same equation, and that may make it easier to compare so you’re looking at the same change in number of moles of gas. That might help you better see the connection between phase change and entropy
Yea! Why not just aim for the 100%?
@mathman97 if you are talking about this website http://apcentral.collegeboard.com/apc/public/exam/exam_information/221837.html
it says for 2013 and prior
This thread is surprisingly helping me study haha
@JuicyMango - I remember reading about it in Zumdahl…also, the other choices don’t make sense. But yeah, totally didn’t expect something like that to show up on the AP.