Wednesday, 25 March 2009

S205: CMA-2

So - there is another computer marked assignment to do. There are 35 question to be done, and they vary a lot in format. Some you have to work out a number and type it in. Others require ticking boxes, and so on. These have their strengths and weaknesses. Firstly its a computer marking your efforts, although the questions are reviewed by the course team. This does mean you can sometimes get what you think is the right answer only to be caught out on a technicality, like typing 2.0 when it is expecting 2. Mostly though its pretty good at taking reasonable answers - but of course can't apply the same common sense a human can.

You generally get 3 attempts at an answer, unless its a true/false type one. A couple of them I got completely wrong. One was on the symmetry of SeOCl4 using VSEPR - which even after 3 attempts I still got wrong, and couldn't work out why. My tutor suggested some possibilities given I knew the answer (it tells you once you get it wrong). I also checked it out with a chemistry lecturer friend and she came to the same conclusion as I had. After taking it up with the course team they explained (after the deadline) why their answer was right, but eventually they zero'd out the question as it was rather ambiguous. Even given the answer I couldn't see how you could come up with a definitive structure based on just the course notes - there simply wasn't enough data to cover these weird edge cases. The trouble with issues like this is that I find it suddenly undermines my confidence. Its not a silly mistake, its something I've thought about and still got wrong. I suppose whatever doesn't fail makes me stronger, but in reality it tends to lead to a certain fear of similar questions.

The other question I got wrong I could eventually see I'd just made a silly mistake. Its a bit weird doing these things, you tend to get CMA blindness. For instance I'd take all the data given, do all the calculations and come up with an answer - I'd probably check it too - and then look at the screen and see if my answer was there. If it was, I'd tick it, if not then I clearly need to try again. However often you get one of these calculations where you end up doing a load of steps and then the final one is to multiply by 2 -- or is that divide by 2... after due consideration you decide its multiply by 2, see the answer is there, tick and go. Wrong answer. My immediate reaction is not to do any more work (because I'm lazy by nature) but to assume it was divide by 2, and the answer is there to, so tick that and resubmit immediately without rechecking things. Wrong again! This is where you're 3rd chance comes in, and where you should sit down and rework the problem again - rather than phoning a friend or asking the audience.

Anyway - that was the last of the two CMAs in this course.

1 comment:

Anne Harrison said...

wow, 3 years later, I am doing this assignment and googled SeOCl4 and your blog is what came up, the question is still there! Maybe they have changed up other bits of the course or provided more information, so the answer is now determinable!