Letters - September 2009

Future chemists need to be problem solvers

I would like to comment on the recent letter by P. A. Barker on declining examination standards.¹ There seems to be general agreement that the future professional chemist needs to understand general principles, show aptitude for problem solving (not puzzle solving) and to have some background in biology (as well as maths and physics). But if the chemists of the future are going to save our civilisation they also need a background in fuzzy logic and systems thinking so that they can more accurately evaluate the potential consequences of their actions.   

In supporting our students to develop these skills the modern modular GCSE chemistry courses, which include units covering food chemistry, cosmetic chemistry, plastic chemistry, environmental chemistry and aspects of 'how science works', are not as 'dumbed down' as many traditionally minded chemists appear to think. Old fashioned, linear 'O-level' courses with their over-emphasis on algorithmic and propositional knowledge could equally be characterised as being 'dumbed up'. The recent reckless application of propositional knowledge and algorithmic reasoning in the financial sector provides some justification for this viewpoint. 

Of the seven recommendations put forward by the Royal Society of Chemistry (RSC) in its report on The five-decade challenge competition run in 2008,² the fourth calls for curriculum authorities to 'improve coherence between the mathematics and science taught in schools'. I agree with this but regard it as more important than the RSC's third recommendation, which urges curriculum authorities to 'put greater emphasis on quantitative methods in GCSE chemistry'.   

In an excellent textbook aimed at AS chemistry students,³ George Facer starts off by assuming that the reader may have studied 'only' GCSE double award science and not GCSE chemistry. But by working through the early chapters of the book the student is brought rapidly up to IGCSE standard in quantitative methods. Then the student can start using the mole, for example, in real problems, not merely puzzle-solving exercises to satisfy examiners and thus obtain 'good grades'. 

Michael Akeroyd, Bradford College

Temperature - the hot topic of thermodynamics

As a student I could manage Hess's law and its various applications. Not only that, I understood it, at least in terms of 'you can't get something for nothing' as far as enthalpy is concerned. And I could grasp the idea of enthalpy change. However, the rest of thermodynamics was a blur - lots of equations connecting one state function to another. I had little conceptual grasp of the functions involved, but I could manage the algebra needed to answer examination questions successfully. 

The macroscopic concept of entropy in classical thermodynamics was just something else to confuse me but, when I was introduced to statistical thermodynamics, entropy started to make sense. I learnt of the connection between entropy and disorder. I could visualise entropy in terms of the arrangement of particles in space and in terms of the distribution of energy quanta among available energy levels. I had no difficulty in picturing redistribution as a dynamic process.

I read the recent article What is entropy? by Cockcroft and Wheeler expecting to have my understanding refreshed and refined, but was sadly disappointed.⁴ The authors have fallen into the familiar trap of picking on entropy as the bogeyman of thermodynamics. Instead I think that accolade belongs to a function deceptively familiar - temperature. 

I cannot visualise temperature, though the authors say I should. Is thermodynamic temperature easily defined? I think not. Temperature though is intriguing. Its unit is not a composite of the fundamental units of mass, length and time. Is this what makes it tricky? The Boltzmann constant (k) is intriguing too since it is often there to help temperature out. For example, the average kinetic energy of molecules in a gas (E) is given by: 

E = 3/2kT ² 

The ideal gas equation states that:   

pV = nLkT 

(whereL  is Avogadro's constant and Lk = R, the gas constant). And k is also there to turn a measure of disorder without units (lnW) into entropy: 

S = k lnW 

I would have preferred a decent explanation of temperature and its buddy,k. Will anyone oblige? 

Mike Shipton, Woldingham School 

Verdigris

Were other readers of May's Chemlingo surprised to see the patina on copper described as verdigris?⁵ After checking various sources, I found that this description is used, but only rarely, while in general the term only refers to forms of copper ethanoate.  

A good article for high school students on this subject appeared six years ago.⁶ In the teachers' guide the author writes: 'The green material that often forms on copper roofs or copper vessels is often called verdigris, but [it] cannot represent the kind of compounds discussed in the article, since it is difficult to imagine where the required acetate groups might come from. In fact, this "green rust" is a mixture of copper carbonate and various other basic carbonates.'  

As an introduction to chemistry, I set my students a home assignment in which they make verdigris by standing copper-containing coins on edge in a glass with a little vinegar, with only part of the coin submerged. Within a couple of days they have verdigris crystals on the coin. The photos show my results using two different coins. The first (fig 1) is a Belgian €0.20 coin (Cu 89 per cent, Al 5 per cent, Zn 5 per cent, Sn 1 per cent), the second (fig 2) a new Israeli shekel 0.50 coin (Cu 92 per cent, Al 6 per cent, Ni 2 per cent). I used 5 per cent apple vinegar.  

The students are fascinated by the colours and the crystals, which they look at with a binocular microscope, and they come up with so many questions and suggestions for further investigations that I can't cope. Incidentally, I find that these copper alloys produce better crystals than pure copper or copper-coated coins. 

Yehoshua Sivan, Menachem Begin High School, Safed, Israel