There has to be an overwhelming reason to me for changing a procedure including safety, reducing expenditure, improved classroom management, increasing the efficient use of time, more informative chemistry, gaining more insight to chemical processes and responding to the findings in chemical education research. On our CLEAPSS Helpline we get many enquiries about experiments not going as well as "the book" describes. I also mean by “the book” the suggested Examination Board procedures. In the UK, we have moved to a skill assessment of student's practical ability but the Boards still print out "suggested procedures" which we know at CLEAPSS to have flaws. Flaws that have been there for years and no one addresses. When making copper sulfate crystals from copper oxide, students still use the Bunsen burner to boil water to react the oxide with the acid. All that is required is to immerse a boiling tube of the mixture in a beaker of hot water from the electric kettle (A new invention compared to date that this experiment was first published over 120 years ago). Teachers and technicians complain that the spots in paper chromatography are so large, Rf values are diffiult to measure and nothing like the lovely little spots in the text book.
The indestructible crucible is another case in point.
I started looking for an alternative to crucibles as soon as I joined CLEAPSS (www.cleapss.org.uk) as I received repeated reports of poor results for the magnesium/oxygen reaction carried out in crucibles. Students could not lift and replace the lids quick enough or they dropped the lids and they broke; that was caused by tongs not closing correctly because they had been “vandalised” in previous classes. Crucibles would crack apart on sudden or cooling. Using stainless steel and nickel crucibles on a class basis were the only alternatives available but they are expensive. I then got the ideas of using steel bottle tops.
First the plastic insert of the steel bottle top needs to be burned away in the fume cupboard. The mass of the 2 tops and nichrome wire are measured on a 2-decimal place balance and again with between 0.12 and 0.20g of magnesium. The arrangement amazingly fits onto a small pipe-clay triangle, heated strongly for 10 minutes, and then allowed to cool. No interference is necessary at all.
In a recent workshop I carried out with teachers and technicicans, I took their results. See the graph below
It an early stage in the students’ career, the results can be plotted on a graph which contains the line that represent s the mass ratio of magnesium to magnesium oxide. Invoking the spiral curriculum, the procedure can be repeated later and the mole ratio can be found as shown in the table.
So here is the teachers dilemma. Does the teacher ditch the exam board procedure using a crucible and lid when it provides poor results. Poor results have an effect on the student’s appreciation of the subject, practical work and confidence in their skills and ability? Or does the teacher give the students a procedure which consistently gives the text book stated rise in mass on burning and a close mole 1;1 ratio of magnesium to oxygen although it is not like the method provided by the Board. A question on the Examination paper will almost certainly relate to the poorer porcelain crucible method?
Carrying out a gravimetric titration with a pipette and balance is another alternative method and since developing this, I wonder if Friedrich Mohr would have used a balance to 2 or more decimal places, if they had been available in the 1850s, rather than a burette. This gravimetric method is not only easier and quicker to carry out but can be used as an introduction to titration without all the glassware and provide a comparison of methods. There are some advocates of gravimetric titration who say that the volumetric method is outdated.
Another area is in distillation where suggested cumbersome glass delivery tubes have broken and caused injury.
But there was an ingenious solution this dilemma provided by a school technician the other week. He was introduced to the microscale electrolysis of copper(II) chloride solution carried out in a Petri dish and took it back to the school. “It is not like the equipment the students will be asked questions on though” said the teacher. "It will confuse them". The technician provided the answer in the form of a diagram inserted beneath the Petri dish and the teacher was really pleased.