Prologue

In my “Personal View” on syllabus reform (“Chemistry in Action”, no.2, October 1980), I remarked that I was able to integrate some 50 experiments into the two years leading to the Leaving Certificate in Chemistry. Since I have been challenged to show how this could be done I thought it might be helpful if I described how I approach the teaching of this subject. I do not claim that this is the only way, or even the best way, but it is the way as it has evolved in my school over the last twenty years or so. I have five periods a week, two of which come together to form a “double”. This is when practicals are done. I have classes in the 15-24 number range. Every three or four weeks we have “in class” tests.

To set the scene: I usually receive into the class boys and girls who have done some chemistry, and some which have done very little. I reckon that, at some time, I will have to cover the whole course, including preliminary material.

Teaching sequence, including experiments

In my Block 1 we do elementary chemistry and chemical arithmetic; that is, elements and compounds, formulas, percentage composition, empirical formulas from composition, Avogadro’s law, moles, and so on. This usually takes about five weeks. Experiments include

(1) Find x in MgSO₄.xH₂O by heating to constant mass.
(2) Percentage of chloride in BaCl₂ by gravimetry, using sintered glass funnels.
(3) Percentage of nickel in a nickel alloy by gravimetry, with dimethylglyoxime.
(4) Relative molecular mass of chloroform by a Dumas-type method.

Block 2 is a short introduction, from gas laws, into kinetic theory. During this we usually use one double period to do a simulated random-walk experiment on diffusion using dice, and I usually finish this off by obtaining an estimate of molecular size by diffusion of ammonia.

Block 3 is Thermochemistry, part 1. Here we do the usual enthalpies of combustion, formation, neutralisation, etc., and the experiments are

(6) Hess’s law, to find DH for hydration of CuSO₄.
(7) Enthalpies of neutralisation of acids.

Block 4 is back to chemical arithmetic with some volumetric analysis; some have done titrations before, but others have not. Experiments are usually

(8) Estimate concentration of HCl by use of borax.
(9) Some other acid/alkali titration (varies yearly).
(10) Estimate percentage of magnesium carbonate by back titration.

During this block I usually contrive to run over the principal bond types, ionic and covalent, and make a start on chemical electronics. I try, during this, to introduce the idea of shapes of molecules by electron-repulsion theory and also the idea of resonance. It will be seen that I have not at this stage touched orbitals, nor do I intend to; a knowledge of chemistry must precede its theory.

Block 5 takes us into Organic Chemistry. Reactions we usually do are

(11) Preparation and properties of ethyne.
(12) Simple preparation of an ester.
(13,14) Hydrolysis of ethyl benzoate: this occupies two double periods because I include in this the determination of melting points, iodoform test, and so on.
(15) Oxidation of propanol to propanal; reactions of aldehydes and ketones.
(16) An aromatic nitration.

Here I usually demonstrate the catalytic effect of a pinch of iron filings on a solution of bromine in benzene, and talk about aromatic compounds in general. I will also by this time have demonstrated polarised light and optical activity and have dealt with geometrical isomerism. I use the idea of resonance here in dealing with benzene. I don’t at this stage reduce nitrobenzene to aniline, but I talk about the general importance of aniline, and we do:

(17) Diazotisation and three simple reactions, including a coupling.
(18) Preparation of acetanilide.
This gives me an opportunity to introduce, as useful compounds, acid chlorides and acid anhydrides. I can also link up with the peptide bond, and so into polymers. At some stage now will come
(19) Depolymerisation and repolymerisation of perspex.
Also in this general area will be
(20) An experiment on aspirin.
This involves the hydrolysis of aspirin leading to some work on phenols, ferric chloride colours, and such like, and we usually do
(21) Benzamide from benzoyl chloride and ammonia.

By now we need a change; I try to do a bit here about the theory of organic reactions. I know that some would say that I should do this right from the start, but with my very mixed ability classes I find it preferable to bulk it together now; free radical substitution and ionic addition, acidity of phenol and a simple introduction to Markownikoff and direction of aromatic substitution. Experiments round here might include

(22) Preparation of bromoethane (and the reactions of alkyl halides).

At this stage we are into the summer term, and we go back to kinetic theory for Block 6 and so to Raoult’s law. If I feel strong enough I usually do a Raoult experiment (R.M.M. [Relative Molecular Mass] of naphthol in ether) as a demonstration, but I usually get on quickly to other colligative properties.

(23) Relative molecular mass of urea and sodium chloride (apparent!) by boiling point elevation.
(24) R.M.M. of acetanilide by f.p. depression.
(25) Eutectic curve between naphthalene and l-naphthol. (I know that eutectics are not “on the course”, but it gives a bit of practice and quite a lot can be learnt from it; it has bearings on geology and alloys too.)

Depending on how time is going we normally do about now:

(26) R.M.M. of chloroform by Victor Meyer; this is usually enjoyed because of the ingenuity it allows in setting up.
(27) Silver nitrate titrations.

The time has now come for a bit more theory; we are just about at the end of the first year, and it fits in nicely with my Physics course to get on to spectra. As far as Chemistry is concerned, I like to show spectra of helium (to see the lines) and hydrogen (it is astonishing how many people have never seen this, and actually believe it to be a pure line spectrum!), and a few other things. There are not many experiments strictly relevant, so I usually interlock Block 7 (Spectra) with Block 8 Redox, where there are lots more experiments than theory. So while I move into energy levels, Schrödinger, and orbitals, they get on with some titrations:

(28) Iron(II) with permanganate
(29) Iron(III) with KMnO₄ after reduction with zinc amalgam
(30) Oxalate with KMnO₄
(31) Hydrogen peroxide with KMnO₄
I know that iodine titrations are not on the course, but they are so beautiful we usually do some, say:
(32) Iodine with thiosulphate
(33) Chlorine in Parazone.
(34) Concentration of bench potassium dichromate, via iodine and thiosulphate.

The time has come for more energetics, so back we go to thermochemistry, and on to bond energies. A few more experiments slot in here in Block 9.

(35) Enthalpy of reaction of sulphuric acid with water.
(36) Enthalpy of bromination of cyclohexene, and bond energy of C-Br bond.
(37) Enthalpy of solution of potassium iodide, and lattice energy.
I normally use a double period at about this time to
(37a) Estimate ionisation energies of argon, helium and xenon, and perhaps another one to
(37b) Investigate the polarity of molecules, by plastic rods and also by relative permittivity of solutions. This includes positional isomerism in benzene, and in dichloroethenes. True, in these I do most of the work but there is a fair amount of pupil involvement in taking measurements.
For Block 10 we go to reaction rates and effects on them. Experiments include
(38) Effect of concentration on rate (usually based on an “iodine clock” reaction).
(39) Effect of temperature on rate (usually oxalate and permanganate). For the brighter members we go on to calculate from this the value of the activation energy using simplified arithmetic to help with the exponentials.
This naturally is leading to Block 11, Equilibrium.
(40) Estimate the equilibrium constant between ethanol, ethyl ethanoate, ethanoic acid, and water.
This leads inevitably to Block 12, Acidity and pH.
(41) Find how pH varies during the titration of hydrochloric and ethanoic acid with NaOH.
(42) Set up a range of buffers and observe the colours of some indicators as a function of pH.
(43) Estimate pKa for benzoic or formic acids by half-neutralisation with bromophenol blue as indicator, and find pKIn.
(44) Compare the enthalpy of neutralisation of the strong sulphamic acid with that of the weak benzoic acid. This, as we do it, is actually such a crude experiment that we can learn a lot from discussion of its sheer approximations! Around now I usually get out the pH meter and demonstrate its use, say in doing a titration curve for phosphoric acid; one can also identify which is cis and which trans in maleic and fumaric acids if it is a bright class.

If I haven’t done it before, we have Block 13 on Radioactivity; I show the properties of the radiations with a Geiger counter and we talk about tracers, but we tend to do more of this in Physics. Also somewhere we slot in Block 14 on electrolysis. I would show Hofmann’s voltameter and use it to find the value of the Faraday, and they would do the following:

(45) Find the number of coulombs needed to deposit one gram of copper.
But we do not always do these; it depends on what was done in Form IV and also what is done in Physics. Usually I include
(46) An ion-exchange titration; estimate the concentration of a copper sulphate solution.
By now time is running out; the “mock” is looming up, but it is time for a crack at revision organic chemistry. While they are brushing up on this, we collect all the retort stands in sight and get set up to
(47-49) Reduce nitrobenzene to aniline.
Actually this takes three double periods; in the first we get the reduction done, in the second we do the steam distillation and ether extraction, and in the third we distil off the ether etc. We also frequently have
(50) Hofmann’s degradation (production of methylamine).
So that about completes the course. Naturally one cannot do the same every year; half-holidays, exams, etc. intervene, and some-times you like to try a new experiment or bury an old one. It is also useful to have a few “spare experiments” in hand, such as
(51) Reduction of a ketone with lithium tetrahydroborate (which is useful to introduce metallic hydrides).
(52) Estimate lead by gravimetry via lead chromate.
(53) How much magnesium hydroxide is there in a ‘Milk of Magnesia’ tablet?
(54) Find the equilibrium constant for the reaction between iron (III) and thiocyanate by colorimetry (or use colorimetry to estimate iron).
(55) Analysis of anions (qualitative)

There is really no shortage of experimental work available!

Postscript
However, I admit that the provision of practical work does involve teachers in preparing the apparatus outside class time; it also involves getting washing up done (but a pupil will often do this by arrangement). It means that supplies must be got in, and grants arranged, but in my experience the Government grants are adequate, taken from year to year. Personally I would find it very unsatisfactory not to have students doing practical work, and not to be able to do lots of demonstrations myself. I hope that this article may help younger teachers to do more in this direction, knowing that it is possible.

How much of the above will survive the onslaughts of the syllabus revisers remains to be seen; but I would hope to be able to retain most of it, and it would certainly by my intention to have once again at least fifty experiments to illuminate the course.

From the Editor
The list of experiments above is very impressive and I’m sure we’d all agree that Dr.Somerfield’s pupils are lucky to have such a gifted teacher. Teachers who have attended past Teachers Refresher Courses (1980 for example) will have seen Dr.Somerfield in action and will have appreciated his simple and elegant demonstrations. The results obtained by Dr.Somerfield’s pupils don’t appear to suffer by doing so much practical work: indeed, I’m sure their chemical knowledge, understanding and skills are impressive. But many pupils in Irish schools today do no practical work at all in 5th and 6th year, and this should be of major concern to all involved in chemistry teaching. A variation from one school to another of zero to over 50 practicals is certainly not ideal. The new chemistry syllabus us expected to give more emphasis to practical work and provide more guidelines to teachers on suitable experiments. Unfortunately, this will not ensure that all chemistry students do an adequate amount of practical, or even any practical work at all. I know that many teachers do value practical work and include as much as they can in their teaching. I hope that “Chemistry in Action” will encourage others to take up the gauntlet, and give them ideas and help in doing practical work in chemistry. I would also urge other experienced teachers, like Dr.Somerfield, to share their hard-won knowledge with other teachers. Randal Henly’s book “Practical Chemistry for Today” (with the associated “Teacher’s Guide”) gives details of over 80 experiments and advice to the teacher. If you want some ideas for experiments that can be done, get hold of a copy today.

“No bubble is so iridescent or floats longer than that blown by the successful teacher.”
Sir William Osler

MOLAR VOLUMES: the molar volume of a substance is the volume occupied by 1 mole of the substance i.e. an Avogadro number of molecules. This volume changes from element to element and from substance to substance, although each contains the same number of particles (atoms, ions, molecules) as the mass and size of the particles changes. It is quite a good idea when teaching about the mole to illustrate it, not only by doing problems, but by showing pupils or better letting them weigh out moles of different substances, and having them labelled in bottles as a display e.g. 1 mole of calcium carbonate (100g); 1 mole of sodium hydroxide (40g); 1 mole of iodine (127g); 1 mole of methanol (32g); 1 mole of water (18g); 1 mole of gas (see above for a model of 1 mole of gas) etc. The display can be as large as you like using substances that the pupils have already come across and is easily made up using a top-pan balance. The rich variety of states of matter, texture, colour and amount have only one thing in common – the number of particles, the number of moles.

NO PRETENCE!
“…there can be no pretence about teaching and learning. In the acquisition of scientific information, for example, the teacher may set up an ‘experiment’ in which the pupil has to ‘find out’ what a result will be.
Now part of such experiments may be the acquisition of skills and so far they are legitimate. But very often there is a profound bogusness about them, if the pretence is that the outcome is unknown. Indeed, if the outcome is not what is expected, the ‘experiment’ is usually by-passed and recourse has to be made to the textbook instead.”
Mary Warnock
TES 19/12/80