MAY13 Chemistry HL Paper 1 and 2 TZ2

[IB-Adam]

Some questions:

4) For the question in P1, which is a lewis acid base reaction but not a BL one, I put B (I cant remember what the answer was) does anyone know the right answer? No one at my school knew for sure.

I took B since it involved no proton exchange (Bronsted Low.. theory), and because I directly saw that another complex ion was produced in B. Complex ions are formed by ligands sharing their electron pairs to the central ion --> Lewis Base theory..

[IB-Adam]

For the Kc equilibrium, I have seen similar problems before. The trick is to notice that you are able to take the square root of the expression without even having to use your calculator.

Why? If you got it right, your Kc = (A)^2 / (B)^2 = (A/B)^2

You can easily take the square root of this!

[Johanna St]

I actually thought some questions on paper one were quite challenging, like the acid base one. I also thought the question 40 was unusually difficult as I found the answers too subjective. I said it was accurate and precise, because the differences in pH would actually be minimal if converted to Hydrogen ion concentrations, but who knows. And on the acid base reaction question I also said B, because the others all seemed to involve transfers of protons.

And paper 2...well I hated most of the calculations, because I am a person that does silly math errors, especially when under stress. And only giving one mark on most of them did not help me, cause that means I can't even get credit on working. How did you guys calculate the activation energy, because I multiplied the negative gradient by 8.31. My gradient was 14, and my answer was 116 I believe. but that was totally different from what the others had :/ Hope I can still get a 6 in chemistry, although I did stupid mistakes

[Johanna St]

oh and the question with the lattice enthalpy, I was a bit confused. Because they were talking about the most positive lattice enthalpy of dissociation, and they have not used that terminology before. I was confused because does it require energy for the dissociation, which would mean the stronger they are held together the more negative it was ? So therefore the right answer was the one with the largest size adn the smallest charge?

[IB-Adam]

oh and the question with the lattice enthalpy, I was a bit confused. Because they were talking about the most positive lattice enthalpy of dissociation, and they have not used that terminology before. I was confused because does it require energy for the dissociation, which would mean the stronger they are held together the more negative it was ? So therefore the right answer was the one with the largest size adn the smallest charge?

In other words, they were asking for the strongest lattice. --> MgCl2

Mg had the highest positive charge whereas Cl was the most electronegative --> Really strong bond.

[Johanna St]

OH man, I actuall know that stuff but confused myself because of the different wording :(thanks

[IB-Adam]

For the first order reaction question, which graph was it? C or D? D was the concentration-time graph which didn't seem to reach 0 at all, whereas C clearly approached 0.

[Johanna St]

I had D for the graph because of the gradient

[Andrei D]

I did the orgo one. Also acids and bases one. Section A was tough but doable. I also wrote imprecise and inaccurate. I'm pretty sure it's inaccurate since like @IB-Adam said, it increases exponentially and the mean wasn't even the same value (I think). I'm just not sure about the precision since that's pretty subjective, although I just compared it to the given value which had three sig figs so I thought compared it's imprecise... Not too sure.

Some questions:

1) What did you guys do for that question with HF and NH4F?

2) Do we all agree that the equilibrium question was off syllabus? Since you had to use quadratics no? (There's a syllabus statement that says that the use of quadratics will not be examined)

3) Iron in the human body?! I wrote helps produce red blood cells is that right?

4) For the question in P1, which is a lewis acid base reaction but not a BL one, I put B (I cant remember what the answer was) does anyone know the right answer? No one at my school knew for sure.

Man what are you talking about, off sylabus lma0! It clearly said that Kc = 53.something -> You could calculate the initial concentrations, and its clearly stated that when Kc is MUCH larger than 1, the reaction will go to completion -> Eg. the final concentrations of reactants will = 0 and hence the HI final concentration was bassicaly 2x the initial concentrations of reactants (they were the same).

Overall I found Section A to be too specific at partsbut the calculations were easy. Did 5 and 8 on Section B. 8 went perfect and 5 I missed a 4 point question due to lack of attention. I was hoping for a 7 but after that crappy section A I think I'm going to get a 6.

Edited May 17, 2013 by Andrei D

[IB-Adam]

I had D for the graph because of the gradient

Perhaps it is D, and that they wanted us to recognize that C only worked for a second order reaction. From a mathematical perspective, I think that the question was unfair.

[IB-Adam]

How did you guys calculate the activation energy, because I multiplied the negative gradient by 8.31. My gradient was 14, and my answer was 116 I believe. but that was totally different from what the others had :/ Hope I can still get a 6 in chemistry, although I did stupid mistakes

I got 50 kJ/mol I think. Your method is correct so either I or you will only lose one mark out of three. I hope you'll get your 6

[Johanna St]

There probably was a mistake in the graph because it did not approach zero and the second order graphs given in all my books looked different to D in that respect. IN general I think many questions were either awkwardly asked in respect to wording, or seemed to have answers with errors....

[Bennyboii]

Paper 1 went much better than it did in my mock exam in my opinion some of the questions were rather simple and others took time.

Paper 2 was a nightmare!!!!! We were never taught topic 11 on uncertainties so basically we lost marks there then the calculations were just worded confusingly so we were all screwed. AND worst of all our lecturer told us that their would be a big organic and a big transition metal question because there has been in the past 3 years.But only a big organic came up meaning we automatically lost 25 marks from the whole paper :/ I did question 6 in section B and I could only manage to get half of the pH calculations done because I had no idea what to do =( Hoping that the paper 1 & 3 boost my grade because they were good papers.

[spacemonkey74]

For the first order reaction in paper 1 i chose C, it did not approach zero but i think that was sorta the catch of te question. They had quite deliberately put values on the y axis, enabling u to calculate the half life, only first order reactions have a constant half life, and only c had a constant half life

[Ezak]

I did some frustrating second grade equation for the equilibrium one, like let [i2]=[H2]=x now [HI]=2.4(or something)-x then did it like a second grade equation.

[vaido]

Paper 1 was alright but paper was a nightmare. That equilibrium question already made me lost 4 marks . Was about to work it out using quadratic but the syllabus says quadratic are not examined. Didn't have enough time to do it at the end and just skipped it. (((

[Brodia18]

Did anybody do the the TZ1 papers?

[Usman Khan]

I found paper 1 and 2 to overall quite good, except the first question of section A on P2. I can't believe they wanted us to remember the reaction of limestone! I think that was quite unfair on their part. Also, what did you guys put for the type of error for the meniscus reading? I put random error, but I don't know if that's right at all. Also, what could they have done to reduce the brown precipitate from forming? I didn't know what to put at all for that. But other wise, it was pretty good. I did questions 6 & 8, both which were quite straightforward.

[Johanna St]

I said it was a systematic error, as the readings would have all been off by the same amount. And I said that they should reduce the amount of oxygen available, as the percipitate formed in the reaction of Mn2+ with oxygen. but I am not sure they'll accept it, I just guessed for that one

[IB-Adam]

I said it was a systematic error, as the readings would have all been off by the same amount. And I said that they should reduce the amount of oxygen available, as the percipitate formed in the reaction of Mn2+ with oxygen. but I am not sure they'll accept it, I just guessed for that one

The thing is, this isn't even in the syllabus. Let's bomb the IB in Cardiff!!!!