Keith S. Taber
Bert was a participant in the Understanding Science project. When interviewed in Y10 he reported that he had been studying electrolysis in chemistry:
"that's where different elements are, are taken out from a compound…there's a positive anode and a negative cathode. And what it does it attracts the positive part of the compound to the negative cathode, and the negative part goes to the positive , to, you know, so that they can erm get the different elements in the different places, so they can just have one element on its own".
To fully understand what this means from a chemical context the learner needs to appreciate the chemical distinction between elements, compounds and mixtures, so I asked Bert what he thought a compound was:
It's erm, it's er two, er you know, it's just a lot of different elements put together – to create just one.
So if I went and got some elements, let's say I went and got a little file of carbon, a little file of sulphur, a little file of copper, er a little file of magnesium and I were to mix them into a beaker, maybe get a glass rod, give it a good stir, er, give me a compound?
Erm, so it's carbon, erm, carbon, sulphur, magne¬. Carbon, er – What's the fourth one?
Carbon, sulphur, magnesium and copper I think I said.
And copper. All right, erm. Copper, copper sulphate and – and carbon, and I think carbon and magnesium might go just as elements.
Okay, so if I ignored the carbon and magnesium,
Yeah.
if I took some copper and some sulphur,
Yeah.
and mixed them up together,
Yeah.
then I'd get copper sulphate.
Yeah.
And that's a compound now?
Yeah.
In chemistry there is a crucial difference between a mixture and a compound: one which it appeared Bert had not at this point acquired. Presumably his chemistry teacher, in teaching the topic of electrolysis was assuming students in the class would apply prior learning about the difference between elements and compounds, so as to appreciate the significance of electrolysis as a technique which brings about an energetically unfavourable chemical change. This prerequisite knowledge appeared to be lacking for Bert, which provided a deficiency learning impediment when it came to understanding the teaching on electrolysis.
Read about learners' alternative conceptions
