Consider the following typical IB question for HL Option C: Chemistry in industry and technology.

“Discuss the properties needed for a substance to be used in liquid-crystal displays.”

Discuss is an Objective3 command term. The definition of discuss is, ‘Give an account including, where possible, a range of arguments for and against the relative importance of various factors, or comparisons of alternative hypotheses.’

This would seem to be very much an Objective 3 type question. The sort of factors a student might wish to include in such a discussion would be:

                The chemical stability of the substance

                The ability to maintain a liquid-crystal phase stable over a range of temperatures

                The necessary polarity in order to change orientation when an electric field is applied

                The necessity for a rapid switching speed

A student who included these four factors in their answer is likely to score very highly and they have indeed had to draw upon their knowledge of Chemistry to construct a suitable argument. There is just one problem. In reality this is an Objective 1 question because all they have had to do is recall what is written in the syllabus. If you look at C.6.5 you will see that both the question and the four properties are all listed. One of the problems of using command terms and giving very detailed notes in the syllabus is that students often are not required to think and select relevant factors for themselves they just need to repeat what is on the syllabus. This is one of the reasons why many teachers and students spend so much time practising with past papers. I once analysed the 25 mark Option D section of a HL Paper 3. Although superficially it had twelve Objective 3 marks according to the command terms used in reality 24 of the marks were objective 1 or 2. Strangely the only truly Objective 3 mark out of the 25 was for identifying a chiral carbon atom on a molecule they had not seen before. The command term used for this question was ‘State’ which is Objective 1!

A few years ago when I was writing the IB Paper 2 I included a question which did not have a ‘right’ answer. The markscheme basically said that if the student says ‘yes’ and gives a valid reason then give them the marks and if the students says ‘no’ and gives a valid reason then also give them the marks. The external advisor’s comment was that you cannot have a question which does not have a right answer in a Chemistry exam! The question was cancelled. But why do all Chemistry questions have to have ‘right’ answers? Other subjects such as History do not always have right answers. The Objective 3 skill is to construct an argument and give the strengths and weaknesses of opposing views. To see how my students would respond I gave them an end of year exam which had some typical IB-type questions then one final genuine Objective 3 question. The question was, “Which is more reactive, a sodium atom or a sodium ion? Explain your answer.”

You might like to think how you would answer this question – which does not start with a command term (but does have one in the second sentence).

The initial response from most students was that sodium atoms are more reactive as they readily lose an electron to form a sodium ion. Sodium ions have a noble gas configuration so are expected to be very unreactive. The experimental evidence is that if you put sodium metal on water then a vigorous exothermic reaction takes place and hydrogen, hydroxide ions and sodium ions are formed (with a suitable equation) whereas if you put salt (sodium chloride) in water it merely dissolves and the process is slightly endothermic.  Put more succinctly, you put sodium chloride on your fish and chips you do not put sodium metal and chlorine gas separately on them!

However the student who thinks critically will go much further than this. What sort of sodium ion is being referred to in the question?  Salt is not a sodium ion it is an ionic compound of sodium ions and chloride ions. If the question refers to sodium ions combined in a compound then the atoms are more reactive but what if we look at free sodium ions in the gaseous state? In fact, when you remove an electron from a sodium atom the process is highly endothermic. You need to put energy in to turn it into the gaseous state then you need to put more energy in to ionize it to form the sodium ion. The reason why the reaction of sodium metal with water is so exothermic is because of the large amount of energy released when gaseous sodium ions become hydrated by the water to form Na⁺(aq).  If they feel uncomfortable using hydration energies (which are not strictly on the syllabus) then a similar argument can be made using the formation of sodium chloride from its elements and involving the lattice enthalpy. By drawing on their knowledge of Born-Haber cycles a good student can deduce this for themselves. I wish IB exams gave more scope for students to really show what they understand rather than more often asking them to simply repeat back what is on the syllabus.