CLEAPSS is carrying out a review of standard experiments for the UK chemistry syllabuses, now that I hope we have a more sensible approach to practical assessment of students. Students need to be assessed on their skills rather than carry out contrived, constrained procedures under so-called exam conditions. I am convinced that these practical exams stifled innovation and development of ideas in chemistry teaching.
Teachers need to observe students demonstrating techniques correctly and in the meantime, teachers can discuss observations made by students, discuss the chemistry at a nano-level, assist with the maths, discuss the industrial and environment issues of possible larger scale operations in chemical engineering, engaging the student in a friendly way, etc. Yes teachers will be teaching. Students will be asked to have a lab workbook in which could show, methods, photographs, results etc, just like research chemists do. Recently graduated teachers will have never taught in this manner before, having been spoon-fed some rather strange practical experiments from exam boards and text books. The exam board was using the practical exam to discriminate between students. The authors of text books are mainly involved in explaining chemistry to students.
We have begun to look at some post-16 organic practical chemistry procedures and some interesting observations are emerging. Many dismiss preparative organic chemistry as mere cookery, ie, following a recipe, and hence showing all what is “wrong with teaching”, ie rote learning and retention of facts. In practical organic chemistry, there appears to be no “inquiry” “modelling”, “flipping”, “IT”, “STEM” ie, all the buzz words that float around in chemical education theory. Practical organic chemistry is time-consuming in technician preparation and student teaching time and in clearing up. It uses complicated and expensive equipment. It can go wrong with lost product on the bench, little fires, erupting chemicals, spills etc. Organic chemicals smell and some think we can only do preparations in expensive banks of fume cupboards rather like University Chemistry departments.
Recipes: School organic chemistry is Vogel divided by 5 or 10!
Vogel’s Practical Organic Chemistry was a standard text in our University chemistry departments. You can see from this extract from the 5th edition for the preparation of 2-chloro-methylpropane (2C2MP) from 2-methylpropan-2-ol (2MP2) that in many school texts all we have done is to divide the Vogel volumes by 5, so that a 50-ml separating funnel is used. We asked why do the reaction in a separating funnel when we all know about leaky taps? In our updated method we suggest carrying out the procedure in a conical flask with a cotton wool plug then doing the separation, cleaning and drying in the separating funnel and finally distilling this highly flammable liquid with hot water from a kettle, not direct heating with a Bunsen burner..
It can be more than just following a procedure
One exam board has recommended using the addition of anhydrous calcium chloride as in the Vogel method (note 1); another version suggested using reagents cooled in a fridge at the beginning, some older versions of this method suggested a precise times of 10 minutes and 15 minutes to leave the mixture. As the ultimate aim is to obtain a good yield we can ask students to look at improvements to a basic method as a part of an inquiry process.
Teachers should not talk too much at the beginning of a practical lesson; all you are doing is overloading the student’s short term working memory. “You set it like this and then you do this”; “remember to add this”; “now look at the way I use a separating funnel”. All the instructions can be given to them the lesson before and they may be able to look at videos but importantly ask them to call you over when they first encounter the tricky skill of using the separating funnel. There must be total vigilance by the teacher. Practical is not a time to sit back and catch up on marking. Another issue is the length of a lesson. In many schools, the good fortune to have 2 hour or even longer sessions is disappearing. Taking a University prep and repeating it at school will not work. So a procedure needs to highlight certain places where the student can put the product in a labelled container for use in the next lesson. An advantage is that any Quickfit equipment can be washed and dried in an oven for the next meeting.
You need lots of fume cupboard because the chemicals smell
Odour does mean that you are exposed to the chemical by inhalation but these procedures in schools are not going to cause distress. There are rules about working in conditions where there are chemicals in the atmosphere and CLEAPSS as an organisation takes into account the legal limits set by Health & Safety Regulations. In this reaction concentrated hydrochloric acid is used but the reaction takes place at room temperature or below and if a wool plug is inserted in the reaction flask, the amount the loss of vapour in minimal. In addition, as the reaction proceeds, the acid is diluted in the process so loss of hydrogen chloride gas becomes a non-issue.
Organic chemistry at University is going to use (to school teachers) more exotic and hazardous chemicals such as thionyl chloride, pyridine, lithium aluminium hydride, tetrahydrofuran when a fume cupboard is essential. Refluxing is a very efficient process in that the boiling liquid is completely condensed in the condenser.
However, the person who is most likely to complain about the smells is the lab technician when clearing up. Quickfit with reagents should never be left overnight to dry out. It is at this point that the joints can seize up. Place a bowl of hot water with a dishwasher tablet in it in the fume cupboard in which the students can place their glassware. The water should be drained off and poured down the toilet and the equipment rinsed and placed in an oven at about 80C to dry. In that way, you may just get dry equipment the following day!
Green organic chemistry
Teachers need to be more familiar with green chemistry as it might remove some of the preconceptions amongst some students that chemistry is a rather dirty and polluting science. Green solvents (preferably no solvent), high atom economy, heterogeneous catalysts allowing quick removal of products, low toxic reagents, low toxic waste and recycling of reagents are all part of the green revolution in organic chemistry. We need to produce chemicals that can be used in more experiments in the school term. The product of this reaction can be used to make 2-methylpropene; with a Bpt of 51°C, it can be used in a procedure to measure its molar mass; it could also be used in Friedal Kraft reactions.
Microscale organic chemistry?
It is possible to reduce the scale of this reaction by a further factor of 5 and use microscale equipment. The cost of microscale is no different from our school semi-micro. Also it does not reduce the time of the experiment. Separating funnels are not used but Pasteur pipettes are used (which provide extremely good separation of layers). This does not tick a box in our skills we have to teach we have to teach and the procedure will be alien to most teachers. Heating such small equipment is also a problem in UK schools as we do not have electrical heating. So although it has many interesting ideas, pure microscale is at present a non-starter in UK schools.
But cookery could be organic chemistry
Have you always got the right ingredients when you follow a cooking recipe? I find I start with good intentions and realise I have forgotten to purchase an ingredient. But you could always use and alternative. Sometimes it works, sometimes it doesn’t. So, to my mind, TV cookery programmes show the “flip” idea so common in our chemical education research articles and changing the ingredient shows the inquiry method at work. Nothing is new in teaching.