AS level Examination Hints

Ask yourself the following question before you read on:

What am I trying to do in the examination?

  • Do not use red ink.
  • Do not use tippex. Tippex is not allowed in an examination. Just cross out your error. Do not write over your mistake. It may not be clear and therefore marked incorrect.
  • Handwriting that is impossible to read cannot earn marks.
  • RTQ2Read the question at least twice (or even three times).
  • Make sure that you have answered every part of the question.
  • State and explain the trend requires you to begin by stating the trend and then giving an explanation for it.
  • A calculation question sometimes asks for a comment on the result; don’t forget to do it.
  • Read through your answer at the end and make sure that it makes sense.
  • Read your answer and check that your answer is the answer that the question has asked for.
  • Show clearly all steps in calculations. This might give you marks even though your final answer may be wrong
  • NAUTE No approximation untill the end. Do not round off untill the end of the calculation.
  • Don’t forget to write state symbols in chemical equations.
  • Check the chemical formulae of each compound you write. It is quite easy to make a simple mistake. E.g. NaCO3 when it should be Na2CO3
  • Layout calculations in a comprehensible manner and don’t forget to quote the units at the end. Do not forget to include the sign when asked for, even if your answer is positive. Give you final answer to same significant figures as quoted in the question
  • When asked for observations say what you would see and not a deduction e.g. in a reaction you would not see carbon dioxide gas but you would see bubbling.
  • Understand the difference between colourless and clear. Water is colourless but a cola drink is clear.
  • Sketch does not mean a scruffy attempt. Diagrams must be neat, accurate and fully labeled. Don’t forget to label the reagents. Practice drawing of apparatus. Make sure that air gaps are clearly shown other wise the apparatus should be sealed. In diagrams showing organic preparations or separation (e.g. reflux, distillation) ensure that all joints are sealed. In distillation the thermometer must be positioned in the correct place.
  • When drawing dot and cross diagrams don’t use the atomic number to work out the number of outer electrons but use the group number. E.g. Bromine would give 17 electrons in the outer energy level, but you only need to use 7 electrons.
  • Graphs must fill the graph area or graph paper that has been provided. Axes must be in ink and the line drawn in pencil. The data points must remain visible once the line is drawn. All data for plotting graphs except for ionization energies are continuous. They must therefore be drawn with a smooth curve or line of best fit, not dot-to-dot.
  • Know the difference between molecular formulae, structural formulae and displayed formulae. In displayed formulae show all the bonds and if ionic then charges must be given against each ion. Students tend to forget the 0-H bond in alcohols
  • "Define" can sometimes be best illustrated by giving an exemplar equation.

    • e.g. the definition of rate constant k is k= Ae-Ea/RT
  • Note that rules are not an explanation. Rules tell us what we do and not why. e.g. Octet, Markownikoff etc.
  • When asked for reagents, state full name or full chemical formulae with state symbol; e.g. sulphuric acid or H2SO4 (aq) and not H+.
  • When refluxing, state conditions.
  • Referring to feasibility of a reaction using D H, you must use the sign. e.g. reaction is not spontaeous because D H is positive
  • Mass spectroscopy is a good method of identification of a material. pH cannot always be used as way of identifying an acid.
  • Be precise when asked for uses or effects e.g. PTFE is not "used in cooking" but as a "non-stick surface on cooking utensils"; chlorine is not "used in swimming pools" but as a "disinfectant in swimming pools"; "oxides of sulphur may give rise to acid rain" is not sufficient but "acid rain may affect plant growth"; "greenhouse gas or greenhouse effect from the emission of carbon dioxide" is not sufficient but "its consequence is that it may cause global warming".