One on the objections to devising new equipment or novel procedures is the cry from some teachers that students will be at a disadvantage because the examiners will not ask questions about that procedure in the exam.
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.
The indestructible crucible is a case in point.
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.
The indestructible crucible is a 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.
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. | |
Invariably every group, obtains an increase of mass, which does not happen with crucibles. Secondly, the ratio is close to 1 to 1. (As magnesium nitride is obtained as well (add hot water and ammonia is obtained), the increase on mass should be slightly lower than that expected. There is large amount of black material left in the product. it could be a silicate from the manufacturing process of magnesium ribbon..)
E: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?Of course Student’s could carry out both methods. The teacher could demonstrate one method. These procedures are not exams, as they used to be, but are assessment of students’ skills.
You only have to read whan Exam Board wites in writes in its notes and the comment from a person at a meeting on practical work
You only have to read whan Exam Board wites in writes in its notes and the comment from a person at a meeting on practical work