Friday, 26 June 2009

S283: TMA-2

TMA 2 comes around, and there is more work to do on book 1 in this one. It has just the 4 questions.

Question 1 is about atmospheres. You have to start by discussing techniques for analysing atmospheres. This is followed up by some calculations on partial pressures and what sort of conditions could make for frozen carbon dioxide on the Earth and Mars.

Question 2 is about Keplers laws. It starts by getting you to state them, and then apply them to an asteroid. Based on this and some other data you then have to work out what sort of asteroid it is, and whether it is a potential threat to the Earth.

Question 3 is an essay! Its 600 words comparing and contrasting the atmospheres, structures and properties of Jupiter and Neptune. Well 600 words is either a lot, or not much depending on how much you have to cover. In the end, with some diagrams and tables and a couple of photos this turns into not too bad an account, but its when do you declare it finished!

Question 4 you are asked to discuss various theories of solar system formation. Based on the latest exoplanetary observations, it seems fairly clear that the current models are inadequate, but anyway to get the marks you have to describe what the books tell you.

Not too bad a TMA, and a lot better mark than the last one.

Saturday, 20 June 2009

S205: The Exam

So the exam day dawns. I generally try to work through as many past papers as I can before an exam. Usually going through them 2 or 3 times.
The first time through is very slow, as I usually can't do or get stuck on nearly every question, or have nagging doubts about the answer. Either way, it means rereading sections of the books.
By the second time through, I've usually got better and can answer some of the questions without help, and others I still have to look up and check.
By the third time through, I'm no longer doing all the questions and only focusing on the areas I want to do. By this time, I'm starting to remember the answers anyway, so there isn't a lot of point going through them again.

So this plan worked well, although I quickly realised I just wasn't going to do much on book 9 - there is just too much seemingly random stuff in there to learn. I found the kinetics and molecular modelling and NMR/IR all quite good - but they are often in the same section so end up mutually exclusive.

There are 4 sections to the exam:
  • A is short answer questions - you answer 8 out of 12
  • B, C, D are long answer questions, and you do 1 from each section out of 3.
A questions are from all over, some can be answered in a couple of words, or with a simple diagram, others require maths of explanations. So its good to pick out the really short short answer ones, and build up some time for use later.
B is usually organic reactions and synthesis. Usually a retrosynthesis with analysis and some of the forward steps required. The rest are more conventional diagrams, but lots of curly arrows required (I took in a green pen just to draw curly arrows with).
C is typically kinetics, molecular modelling and NMR/IR stuff
D is often VSEPR, symmetry, and maybe some spectroscopy, thermodynamics (mainly Born Harber cycles) - and something on book 9.

Once the exam was a couple of days away, I sat down and did a timed exam using the sample exam paper they provide. This is good for showing up weaknesses, but very good for working out how much time you will have for different sections.

Anyway, in this exam I found a reasonable 8 I could do - I know your suppose to read the paper and digest, but I rushed straight into question 1, its nearly always of the same form. Fill in an orbitals diagram from an element. A nice easy 5 marks, as long as you get it right! In my mock I filled in 16 electrons when it asked for 14.

Question 2 was also so easy - I happened to know the answer, that I just wrote it down. You had to identify a compound from 4 possible options, and it happened to be very similar to a past paper - so although it was a book 9 question - I just knew it (or hope that is the case!).

Then I had to pause, and flicked through the whole paper.
I sorted out the ones I could do in the A section, and picked a couple of likely looking long questions. I worked through the A questions, leaving the thermodynamic one to the last, as that although fairly easy (and you can often check you got the right answer in the data book) it takes a little time and is easy to miss out a 1/2 or similar bit.

As usual, there is one that you can answer most parts of and one bit you can't, should you do this question or pick another one?

In the end I did about 10/12 from A, just in case (as they take your best marks). Also 5 long answer questions. I hope it's enough.

Monday, 15 June 2009

S205: TMA-6

Last and final TMA, and one that gave me considerable heartache! Its mostly on book 10 which is full speed organics.

Question 1 is about the production of biodiesel. On the face of it, this looks a nice simple question. However the mechanism is basically a transesterification, related to saponification (soap making). Now both those words sound long and complex, but actually the reaction is really very straightforward. There are two parts to the question, the first is to predict the products of the reaction.
The second is to draw the mechanism.
Well firstly, I usually need to draw the mechanism to be sure I know what the products are, but thats OK I can do the second bit first. The real issue though is there are 6 marks for the first part, and 19 for drawing the mechanism. Even if I do it in painful detail, I can really make more than 2-3 maybe 4 steps out of the whole thing. For 19 marks, this sounds warning bells that I've misunderstood the question. I returned to the question time and again looking for the missing part, even donwloading a research paper on the topic - but no it appears it really is that simple!

Question 2 is some basic organic reactions to extend alkane chains. One part you need to pick appropriate reagents, the other part two different directions for the same reagent. Fairly striaghtforward, but after drawing the mechanisms of the two reactions, I've got a lot more diagram than Q1, and this is only worth 15 marks for the whole question.

Question 3 is on radical reactions - rather scary reactions that have been tamed in recent years. Gives me a chance to draw fishhook arrows, but its basically derived stuff from the appropriate chapters.

Question 4 is on retrosynthesis. You have to undo the reaction to find the products and a way of bringing it about. It leads you through the steps as part of the questions quite nicely, provided you get the right bits. There are some comments on steroechemistry, and on reagents you might need to bring about the final results. Just a case of working through it really.

So - that is all the coursework done! Just the exam to look forward to :-/
(However - I ended up getting the best mark for this TMA out of the whole course, so Q1 must have been "just that easy").