Dissection of a GAMSAT question

www.emergencyone.com.au

Hi again to everyone

Ok it's time to put my money where my mouth is with respect to the whole "reasoning skills" thing. As you may or may not know, my wife and I run a company that offers training in reasoning skills for the GAMSAT. Here's the proof in the pudding as it were.

I'll be referring to examples in the ACER GAMSAT test materials published on their website. I cannot reproduce them here for copyright reasons. Hence I'll list the book, section and question with a description of the question, but I'm afraid you will have to refer to your own copy of the book. It is kind of essential for preparation and you can get a copy at the ACER website here. FYI, I don't receive commisions for that link/book sales and ACER do not endorse any providers of GAMSAT preparation courses or materials (myslef included).

So here goes, I solved this one with my wife. I solved it very quickly and she was amazed; quick hint it has almost nothing to do with chemistry, it's just basic algebra......observe:

GAMSAT Test Book 1
Green Cover
Section III
Unit 10
Questions 32-35

This unit describes some fatty acids as well as some information about their bonds, their state (solid or liquid) at various temperatures and then a table of several fatty acids. So you must need to know heaps about organic chemisrty and fatty acids right......errrrrrr.....no. In fact you can answer it with year 12 chemistry and lots of good quality reasoning!

Firstly lets identify the key information contained in the vignette
(equivalent to year 12/ first year chimistry):
-fatty acids have a carboxylic acid group (COOH)
-saturated fatty acids have all single bonds
-unsaturated fatty acids have some combination of double bonds

Secondly lets identify what assumed knowledge you need:
-carbon atoms form 4 bonds (year 12)
-the ability to solve a basic algebreic equation (year 11)

Question 32 
You have to pick the set of 3 acids that are saturated. So here's the trick; go back to the vignette and look at palmitic acid. You KNOW that this is saturated (the vignette says so) now count the atoms to get the algebreic formula for a fatty acid; it goes C16, H32, O2. Hence the generic formula is (C8n, H16n, On). If an unsaturated fatty acid has one or more double bonds, then H will not follow the formula 16n; hence a saturated fatty acid has to have twice as much H as it does C. Now that you've identified your knowledge, defined the rules, you just need to solve the problem.

Check the first fatty acid listed in each option to exclude some answers. B is instantly wrong as gaidic acid follows the rule C8n, H15n, On. Then move on to the second fatty acid. D is now wrong as linoleic acid follows the rule C9n, H16n, On. Finally move on to the last fatty acid, we've already established that gaidic acid does not meet the rules; hence C cannot be correct. That leaves us with A. Check it, you'll find that for all three fatty acids, tehre is always twice as much hydrogen as there is carbon.....hence it follows the rules and hence A is the right answer....you've proven it by inclusion and exclusion. That's 1 point....now you just have to do it in 100 seconds and multiplied by 110!!

Question 33
So now look at the drawing of palmitic acid and add a mental double bond. We know that adding a double bond will obligate the removal of two hydrogen atoms since carbon can only accomodate 4 bonds. Look at arachidonic acid, it follows C10n, H 16n, On. We can see that it needs 8 hydrogen atoms to meet the 'saturated rule' above, or more to the point it must have discarded 8 hydrogen atoms in exchange for double bonds. Hence there must be 4 double bonds (ie 4 double bonds multiplied by 2 hydrogens). Hence D is correct.

Question 34
This is an interesting question from a knowledge vs reasoning perspective. Your choices are to know everything there is to know about marganrine (it's really not worth your time or energy) or to recognise that they're really just testing your reading comprehension, logic skills and that you established the above mentioned rules.

We know that saturated fatty acids form semi-solids at room temperature (the vignette says so) and the question implies that multiple double bonds reduces the melting temperature. We also know that the point of margarine is to turn an liquid fat into solid fat (again year 12 chemistry). Now lets look at reasoning. Do we know what effect changing pH will have? No. Do we know what adding an alkyl group will achieve? No (well actually we know that a side chain will lower the melting point, the vignette says so). Do we know what effect shortening the chain will have? No. Finally, do we know what effect removing the double bonds will have? Yes. Removing the double bonds will make the molecule saturated....and the vignette tells us that this will make it a semi-solid at room temperature....and our amazing knowledge of margarine tells us that its nicer to spread than it is to pour!! Hence C is correct.

Question 35
When I first looked at this, I thought I was boned because I couldn't remember the molar mass of iodine.....then I realised that I'm an idiot :) This is really just the love child of Q32 and Q33. More double bonds = more iodine reacting with them = higher iodine value. All you have to do is disprove 3 sets of 3 fatty acids. Option A, capric acid is saturated, hence no iodine will react, hence its iodine number is not greater than arachidonic acid, hence A and C are wrong. Using the aforementioned rules, gaidic acid has 2 double bonds and arachidonic acid has 4 double bonds. Hence the iodine value will be higher for arachidonic acid. Hence B cannot be correct and D can be correct. You can take a punt and leave it at this, or you can check the final fatty acid in D to confirm your hypothesis.

Voila! I scored 100%, within 6 minutes (although it took ages to write this post!!). All it took was very basic high school chemistry and algebra. The moral to this story and the only lesson I'll ever ask you to learn is that;

GAMSAT is a reasoning based exam and not a knowledge based exam!

Don't exhaust yourself learning doctorate level chem, org chem, bio and physics. The required knowledge is relatively simple. Instead invest a LOT of time in puzzles, problem solving and reasoning based materials. Check out MENSA, they publish a lot of this stuff, it's DIFFICULT and great practice.

Better still come to our course, we will spend a whole day running through reasoning (aka fluid intelligence), what it is, how to improve it and how to apply it to the GAMSAT. It works and if you get it right, it WILL improve your score. You can book online here:

www.emergencyone.com.au

All the best with your prep folks!!

**PS: If you're freaking out about how much the GAMSAT and associated prep is costing I have this sage advice. You are well advised to put the cost into the context of $100-400k for a medical school education and the potnetial cost of having to sit GAMSAT multiple times. By all means don't get ripped off, but do ask what it is you hope to learn from any particular prep activity**