Acids and bases, bonding in diamond and historical chemistry

Talk Chemistry

Acids and bases

A user who calls themselves AChem IST  wanted to know how to explain acids and bases to their students: 

Different types of liquid in test tubes

As an NQT I'm interested in hearing from more experienced teachers who can give me some advice on how best to explain the difference between 'concentrated' and 'diluted' acid to my Year 7s. Should I say that concentrated acid has 'more acid in it' than dilute acid? I don't want to mislead by saying 'strong' and 'weak' acids.

Michael Ryan suggested this approach: 

Absolutely right to avoid 'strong' and 'weak'. I suggest that you refer to how people make up orange squash and then show how science has special words. Something like, 'Most people would ask you if you want your drink strong or weak, but in chemistry we would use the word concentrated to say we want a lot of squash and only a little water in the glass. For what most people would call a weak drink, we would say dilute. There is only a small amount of squash in the glass and a lot more water than before.'

The problem with your suggestion about simply having more acid is that a bucketful of a dilute acid could have more acid in it than a test tube full of concentrated acid. You need the 'more acid in the same total volume'.

Alan Crooks used particle theory in his suggestion: 

One of the five key scientific ideas you have to get across at Key Stage 3 is 'Particles', so your pupils should be made familiar with particle diagrams for solids, liquids and gases. You can extend it to 'solutions' and say that a concentrated solution has more particles in a given volume than a dilute solution does. Relate this to acids by calling them 'acid particles'.

Bonding in diamond

The covalent bonding in diamond formed the basis of a question from Julian Dance 

We have been covering giant covalent structures and discussing graphite and carbon. We covered the differences in properties being due to the number of bonds each atom is making to others within the structure, eg three in graphite and four in diamond.

The pupil question is: what happens at the 'edge' of the structure? We have diagrams of the structure and they show the 'final' atom on the edge of the structure only making one bond back into the lattice.

I am teaching chemistry as a non-specialism and would appreciate any ideas as to how to explain this simply to my inquisitive pupils!

Karl Jankowski had this explanation: 

I have always taught that the surface C atoms would probably be bonded to hydrogen to complete the four bonds, but the ratio of H:C would be incredibly small due to the amount of C atoms within the crystal compared to surface. Thereby we just ignore their presence in the diamond crystal.

Nessa Carson added: 

If there really are spare bonds, they either double up to form C=C, if that's geometrically reasonable, or react with oxygen in the air. In nanotubes, the 'dangling bonds' on the ends can cause the edges to curl round a bit to reduce their energy.

There's a short Wikipedia article illustrating the reactivity of these situations and their occasional usefulness.

Historical demonstrations

Katy Alderasked about 'old school' chemistry demonstrations: 

Our school is about to celebrate its 75th anniversary. I have been asked to show/run some typical experiments/demos from, say, 1950/60/70's. Any ideas?

Leonard Winning recommended Chemical magic by Leonard Ford, published in 1953 - a Kindle edition is available. Andres Tretiakov suggested the Chemical demonstrations series of books by Bassam Shakhashiri, some of which were published in the 1980s. 

Bob Worley contributed his reminiscences of school chemistry departments in the 1950s and 60s (including the production of sulfur dioxide, chlorine and nitrogen dioxde gases on the bench). 

Finally, Robert Slinn reminded everyone of the RSC's own Classic chemistry experiments, published originally in 2000 as a book, but now available on Learn Chemistry. 


Speech bubbles

Membership of our readers' group on LinkedIn continues to grow. A popular discussion in November was 'How do you motivate students to learn organic chemistry?' Joseph Chimeno replied: 

First, you must get the students engaged in the material. [.] Give an example of how their lives are affected by organic chemistry, ie certain drugs, manufacturing and new discoveries. Second, you can engage the students in interesting lab experiments such as the synthesis of aspirin. Third, perform a variety of demonstrations that get their attention and their interest. Fourth, develop some interesting educational games that they can play and learn the material at the same time. [.] Overall, make the subject fun and be enthusiastic! 

Devlin Cassidy added his opinion: 

[.] Regular testing is key and shouldn't be something which pupils dread. In my experience pupils benefit from good starter activities which test previous knowledge and ensure that they are keeping on top of the different kinds of reaction/mechanism. Far better this than pupils convincing themselves that they don't like organic chemistry simply because of the volume of reactions which they have failed to keep abreast of. I get my pupils to put visual posters up on the walls of their bedrooms which summarise reactions etc. 

Finally, Anupama Moharil lamented: 

Desire is the problem with the students nowadays. Gradually they are losing their tendency to gain knowledge of the subject. Most of them study it to score good marks and gain admission to some good institute. Day by day the students' attitudes are changing. 

Other recent discussions have included teaching chemistry in context, bridging the gap between secondary and university chemistry education, and classifying hydrogen bonding as an intramolecular as well as an intermolecular force. 

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