A step by step guide to higher and ordinary-level chemistry

When you receive your paper, spend a few minutes examining the content of the various questions and decide fairly quickly which ones you can do best.

Tips for the top

Answer those questions first but do not spend more than the recommended 20-minute time limit.

For each question you choose, take a minute or two in planning your answer (particularly for the descriptive questions) and jot down the main points which you think are required. Arrange them in some sort of logical sequence and when you are reasonably satisfied with that, start writing your answer.

Don't waste too much time trying to think of the answers to some parts of questions. Leave spaces and come back to these later.

Remember to attempt all parts of each question. If you really haven't a clue about an answer, make an educated guess rather than leaving a blank. You won't lose marks for an incorrect answer and you just might pick up a few marks for the guess. It might even be totally correct!

Remember to show the starting point and the various stages in every calculation so that the examiner can follow what you are doing. The great advantage to doing this is that if you make a small mathematical slip and end up with the wrong answer, you can still score almost full marks. If you do not show your approach and method and end up with the same wrong answer, you score no marks.

While incorrect spelling won't lose you marks, be especially careful when writing words like ethanol and ethanal; if it's more like the wrong word than the right word, you will lose marks unnecessarily.

The marks for each part of a question are given at the right hand side of the paper. Most marks are given in units of three, which means that if there are 12 marks for a part of a question, four pieces of information are required. Try and envisage what these four essential pieces of information would be.

In descriptive questions, do not write your answer in essay style. List only the essential steps (and number them if you find it helpful) which you carry out as you do whatever it is. This sort of answer is easier and quicker to write than an essay-type answer. In describing apparatus, a well-labelled diagram is much better, as well as being much easier to do, than a long-winded description.

COMMON PITFALLS

Be sure to look out for those questions in which you are asked for two pieces of information in the one question, e.g. "Give the name and formula for the compound formed when ethene is hydrated." The answers are: (i) ethanol, and (ii)C²H⁵OH. Make sure that you write down both answers.

Another type of question that is often incorrectly answered is the following:

"How could you distinguish between the carbonate and the hydrogencarbonate ions?"

The answer: "Add magnesium sulphate solution" is not sufficient. You must say what then happens and how the result is used to make the distinction.

Another common failing is in answering a question such as: "How would you convert ethanal to ethanoic acid?"

The answer: "By oxidation" is not enough. This is not stating how the conversion is done - it is just the name of the type of reaction.

The answer must say something like: "By heating the ethanal with acidified sodium dichromate solution."

QUESTION BY QUESTION

SECTION A

QUESTIONS 1, 2 & 3

(These questions are based on experiments.)

HIGHER LEVEL

Likely topics here are any of the titrations, organic preparations, determination of relative molecular mass, the rate of the catalytic decomposition of hydrogen peroxide, colorimetric measurement of chlorine in solution, extraction of clove oil from cloves.

ORDINARY LEVEL

Likely topics here are: preparations of a standard solution, acid-base titrations, flames tests, tests for anions, organic preparations, the rate of the catalytic decomposition of hydrogen peroxide, heat of neutralisation.

SECTION B

QUESTION 4

Ten short questions (out of 14) are to be answered. These can be taken from any part of the syllabus.

It is recommended that all are attempted and the best 10 will be marked.

Only short answers are necessary, each generally needing two pieces of information.

QUESTIONS 5 TO 9

These are full questions needing detailed answers.

HIGHER LEVEL

Topics likely to appear here are: atomic structure, orbitals, energy levels, ionisation energy, periodic table bonding and electronegativity, organic compounds and their inter-relationships, thermochemical definitions and calculations, rates of reaction, pH definitions and calculation, Le Chatelier and equilibrium calculations.

ORDINARY LEVEL

Topics likely to appear here are: atomic structure,

energy levels,

periodic table bonding and electronegativity,

organic

compounds and their inter-relationships,

thermochemical definitions and calculations,

rates of reaction,

acids, bases and pH,

water,

Le Chatelier and equilibrium calculations.

QUESTIONS 10 AND 11

These include a choice within each. Both questions consist of several "half questions", two of which have to be answered.

Questions from the optional topics on the syllabus (industrial and atmospheric chemistry, and materials and electrochemistry) will appear here. Other topics from any part of the syllabus may also be included.