@baller55 Thymol blue
And a question for you all: what did you say happened to the zinc air cell as it operated? Did the mass change at all, and if so, how?
Also does anyone know where it explicitly says the curve for last year was ~72%? Or was it just through word of mouth?
And I said mass increased because you were taking oxygen molecules from the air that weren’t there when you weighed it initially.
@michelle426 Increased, oxygen reacted with the zinc to make zinc oxide.
I said it decreased, but I guess I’m wrong. I just thought it was due to the lack of oxygen at the elevation, seeing that the cathode held O2 molecules.
Yes, a memo from CB to AP Chem teachers.
@Mochis1 the cathode didnt hold o2. the o2 came from the air. thats why there was an increase in mass
@skieurope my teacher told my class that the curve is worse for us this year. Is that true of was she just scaring us to study harder?
why thymol blue @Frigidcold
@Frigidcold but the zinc was oxidized into ions though? I asked my friend (top 20 chemist in the nation) and he said it stayed the same, I said it decreased. For the most part, everyone I knew either said decrease or same.
@baller55 The pKa was closest to pH at the equivalence point.
I am so pissed at myself for this FR. I wasted so much time on the acid base debating whether to draw a dip on the curve and whether the pH was right, I didn’t even go through and check all my answers and spend time on other questions I couldve easily gotten. And also the q=mc t not realized the constant was in mols, hopefully I get some kind of partial credit for it and also for the second part, I did the existing energy thing - recyling to show that it was positive, thus taking more energy, hopefully I get that right.
@michelle426: Yeah, I said it decreased, too.
@CanisMajor: And my bad, I meant to say that it was from the air. I’m still confused as to how the mass would increase though. Wouldn’t it decrease to the lack of oxygen?
@michelle426 If your friend is a genius and is right, I’d be so relieved because I actually put that it stayed the same. 
But afterwards, a few people told me it increased because the oxygen from the air reacted with the zinc in the cell. This explanation makes sense, so I adopted it.
@Mochis1 we’re talking about standard operation, not about the higher elevation standards.
@michelle426 It asks to use evidence from the equation though, which is why I think it’s an increase. Even though aqueous components aren’t part of the mass of the anode, in respect to the entire cell, I think parts of the cell in solution still make up mass.
I’m just giving up on this question, I’m assuming I got it wrong xD I’m just hoping my explanations and/or calculations can make up for any incorrect questions ._.
@Mochis1 well think of it this way. In the beggining there was only Zn and then O2 reacts and it becomes ZnO which is heavier than the original Zn. Remember that the O2 is in the air so its presence does not raise of decrease mass in cell until after the reaction occurs and ZnO forms. Also remember le chatelier’s principle, the reaction is Zn(s) + O2(g) becomes ZnO (s). at low pressures the side of reaction with least moles of gas is favored so the production of ZnO is favored. More ZnO is formed so mass increases.
Im really wondering about the rigidness of grading and how it works, I’m assuming they have scoring guidelines already made and everything, but how it works to grade them and differences in who you get as a grader for your answers. I’m really hoping I got a 5, I went through the FR and I think the absolute max missed for me was 15 points, which is 67% so if I did well on MC like I thought, I should be good.
@CanisMajor: Oh yeah, that’s right. Wow, my brain was really not functioning during this test. I studied Le Chatelier’s principle the night before and I can’t believe I forgot such a simple thing xD