when your answer is in fact just your working out …
This is without doubt the most frustrating thing examiners see when marking students’ answers. The student understands the content and has done all the hard detective work or completed the calculations but then fails to answer the question!
What a way to lose marks 😢
Case study: Spectroscopy
Question: The infrared spectrum of a compound composed of carbon, hydrogen and oxygen is shown below.
Given that it has a molecular ion peak at m/z 88 on its mass spectrum, use this information to suggest two possible structures for the molecule.
(5 marks)
The main difference between an answer and working is LANGUAGE!
So what’s gone wrong here?
1. The student has correctly identified the relevant peaks from the IR spectrum but doesn’t seem to appreciate that the peak is because of a specific BOND vibrating, it is not because of a functional group present in the molecule. This has lost them 2 marks.
A perfect answer might read like this:
- the sharp peak at 1700 cm-1 is for a C=O bond in a carboxylic acid group
- the broad peak at 3000 cm-1 is for a O-H bond in a carboxylic acid group
2. The question asks for TWO possible structures but the student has only given one (it happens more often than you might think). Another mark lost.
3. The structure drawn would have a molecular ion peak at m/z 88 because the molar mass of this molecule, C4H8O2, is 88 and yet the student doesn’t say so even though they’ve worked it out. And another mark lost.
This is such a common mistake!
Exam technique tip: slow down and read the question carefully.
Use a coloured pen or highlighter to pick out the key information in the question (exam questions are just asking to be scrawled all over).
Once you’ve answered it double check your answer against the question to make sure you haven’t missed something important and that you have used all the information you were given.
Action points:
• head over to https://crunchchemistry.co.uk/interpreting-an-infrared-spect… to brush up on your exam technique for long answer spectroscopy questions
• download a couple of past papers (AS level papers for just IR and isotopic mass spec, A level papers for mixed spectroscopy questions) and practice writing perfect answers
• use the mark schemes to check you are using the language and terminology that will get you the marks, as well as whether you got the question right
And finally … if you are busy revising for exams right now, then GOOD LUCK!
If this has been useful then please forward it on and thank you very much for reading,
P.s. If you need a little extra help then talk to me about 1:1 tutoring. Just click here to find out more!