What was 6a?
@APChemTeacher do you know how they grade two part questions within the same subsection. For example, on 2D, it asks for which is at a higher concentration and justify. I calculated change in enthalpy thinking bond energy was similar to heat of formation, so did products-reactants. So if I got the first part wrong (I chose fulminic acid), and my justification for my wrong answer was right, do I still get partial credit?
I think the cutoff scores will be similar to 2015.
@APChemTeacher I am pretty sure the unknown sample is a mix of Dye A and Dye B.
@gkdudtlffj I’m pretty sure the unknown sample was Dye A. You couldn’t just look at how far it traveled up the chromatography paper, as the solution itself traveled a shorter distance up. It’s Rf value, however, matched Dye A, indicating that they are one and the same. Furthermore, the question specifically asked for one of the three dyes.
@ImpossibleCube I got 9.6 x 10^-4 g Mg(oh)2
I seriously hope we have a 2015 curve, because I can at least get a low 4 there. When I used the 2016 curve, depending on the MC, I would get a borderline 3/4. >.<
Also am seriously mad at myself about the ecell thing. I flipped it! And then turned it back since my 2s and 3s look too similar and I mixed them up. So I can get a 2/4, I guess…
It’s dye A. It has an Rf value of about 0.5.
Ughh there were some numbers in my calculator but it only saved up to #5… guess I’ll have to wait two months in the dark. I feel like I made some dumb mistake-- for CS2, I remember my grams being 4.5 something… I PROBABLY IGNORED THE 2 SUBSCRIPT FOR THE MOLAR MASSSSS
Could someone explain 6a calculation for me. That is the only short answer that tripped me up.
@hypnotoad107 where did you get the Rf value. Looking over it we weren’t given any numerical values. Or did you mean that it just went up have the distance of the solvent front.
@Traiton17 You have to set up Ksp = 4x^3 and solve for x, which ends up being 1.65 * 10^-4.
Then you have to realize that needs to be the molarity in 100 ml, so you solve for moles (since you are given M and liters) and convert into grams.
The right answer is 9.6 * 10^-4. c: (I’m 93% sure, lol)
What do you guys think the curve will be like? What % to get a 5?
Yeah, the dye travelled approximately 50% as far as the solvent front did so you can estimate the Rf to be .5, therefore it’ll match dye A because it also travelled 50% of the distance the solvent front did. The fraction the sample travels compared to the solvent front is constant.
@averagelowtier That’s what I got as well.
@Traiton17 The expression molar solubility is simplified as Ksp = 4x^3. Solve for x to get 1.65x10^-4mol/L. Multiply by molecular weight (58.3 g/mol) to get grams per liter, then multiply by your number of liters (0.100L) to get grams dissoved in 100 mL.
@gkdudtlffj It’s absolutely just A… A mixture when done in a chromotography experiment would split into its components, so if it were a mixture it would show the two substances seperately, not one combined dot.
@DLithium There is no “double jeopardy” for the same mistake… So if you make a mistake you lose that point, but then get points for anything after that if it is correct based on what you got from the first mistake (unless you make another mistake). For example… In question 1, I expect a total of 3 points between i and ii… If you screwed up and forgot to convert C->K for the PV=nRT equation, you would obviously lose one point, but as long as everything else was correct for i and ii you would get the remaining points.
@APChemTeacher what about for 7? I calculated E incorrectly, but I identified the Titrant based on on my E calculation, and I calculated G based on my E calculation. Would I get a zero for the entire question, or can I salvage at least a point?
@sjman1 If you calculated both E’s incorrectly that would cost you two points. If you found them both to be positive (seems to be the typical mistake), you should have identified the larger + as your answer for bi, and then calculated G correctly from the larger + value… That should get you 2/4 points
What did y’all get for 5C about the change in temperature of water if the C3O7OH was contaminated?