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QUESTIONS AND COMMENTS The Cambridge International A level Chemistry Applications Support Booklet This page refers to the edition of this booklet which was published in 2005. You will find the publication date at the bottom of the back cover. Since I got a copy of this booklet in April 2007, I have been e-mailing CIE pointing out problems with it. Because they don't seem to be showing any urgency about putting things right, I have decided to make public the list of mistakes and poor explanations I have found so far. I have only looked at very limited parts of the booklet in any detail. All the problems I have found so far have come from the bits on proteins (including enzymes), DNA (including protein synthesis), and a few from the section on chromatography. There may well be other problems in the majority of the booklet I haven't looked at properly yet. At the bottom of this page, you will find a suggestion as to how any of you who have been affected by this booklet can put pressure on CIE to publish an improved version. Problems with Section 1: The Chemistry of Life Before I pick out individual mistakes, the most obvious problem with this section is the language used. The author uses a level of language which is quite wrong for his target audience. This syllabus is used all over the world, and a good proportion of people doing it won't have English as their first language. I have taught a lot of bright UK students who would find it difficult to understand some of what is in this section! The presence of mistakes, and poor explanations doesn't help either . . . Page 9 The final paragraph here is extremely difficult to understand. It isn't the least bit obvious that "[at pH 7] arginine will have a net charge of +1 because of its additional amino group." Neither is it at all obvious at a glance why the reverse is true for aspartic acid. The danger is that conscientious students will assume that it ought to be obvious to them, and worry because it isn't. If this information is important to the CIE syllabus (and I don't think it is), then it should be explained properly. If not, it should be left out. I've also just noticed that the paragraph refers to the amino acid arginine, but doesn't give its structure in the table at the top of the page - or anywhere else. That's typical of the general lack of helpfulness of this whole section! Page 12 Anyone who can pick out what is meant by a beta-pleated sheet or an alpha-helix from these diagrams deserves a prize! Try it - look at the top diagram and explain what an alpha-helix is, assuming you were coming across this for the first time. Page 20 I'm pointing out a problem here that I'm not 100% sure of the answer to. I'm not happy with the equations for the conversion of succinic acid to fumaric acid in the centre of the page. This reaction is part of the Citric Acid Cycle (or Krebs' Cycle), and you will find it all over the web. Unfortunately you will find it in two different forms. This is one of them. The other version is from succinate ions to fumarate ions, and is the version I have used on the page about enzyme inhibitors. Both versions can't be right! An active site intended to accept ions is unlikely to accept acid molecules. Biochemists can be very sloppy about the use of chemical names. Several sites talk as if "succinate" and "succinic acid" are the same thing. That's as nonsensical as talking about concentrated sulphuric acid and sulphate ions as being the same thing. This makes trying to find the "truth" extremely difficult. I have gone for the ionic version (i.e. not the one in the booklet) on Chemguide for two reasons.
I'm open to argument on this one - but whichever is right, biochemists really should get their act together and speak with a single voice. This is otherwise potentially confusing to students finding two different versions during their research. But whatever the truth, the author should point out that there is this conflict between various sources and make it clear why he has chosen this version. Page 22 About halfway down the page the author says: "the rate of enzyme activity increases almost linearly (Figure 1.25) for reasons similar to any other chemical reaction." Since when did the rate of a chemical reaction increase linearly as temperature increases? As a reasonable guide, around room temperature most reaction rates will approximately double for every 10°C of temperature increase. So if a reaction rate is, say, 1 at 10°C, it will be 2 at 20°C, 4 at 30°C and 8 at 40°C. Try plotting that and see if you get a straight line! I'm also unhappy with the diagram which suggests that enzyme activity stops at 0°C. Enzyme reactions will be very slow at 0°C, but still going on. Page 25 Four lines under the diagram, the author describes the CH3COO group as an acyl group. It isn't! The normal use of the term acyl applies to groups such as CH3CO. IUPAC gives a variety of less common uses of acyl as well, but none of them include CH3COO. Page 34 The DNA replication diagram is wrong. When DNA replicates, the new chains build in opposite directions. This diagram shows them building in the same direction. This is going to confuse anyone doing biology at this level or who might go on to do biochemistry in the future. There are several excellent animations of this process on the web which illustrate what really happens. Try this one for a start. On my page about DNA replication, I have tried to avoid giving any impression at all of the directions in which this happens. I am trying to keep it as simple as possible, but without giving any wrong information. Page 35 A few lines from the bottom of the page, you suddenly come across the terms 5' and 3' for the first time. When I first skimmed through this section, I assumed that I had missed the explanation. But there isn't one. The terms appear for the first time in a diagram on page 31 with no explanation at all of what they mean - or even that they would turn out to be important. That's hardly helpful. Page 40 The second diagram on this page is impossible to understand without quite a lot of explanation (which is missing), and is also wrong! I traced a probable source of this to a Scientific American article. Compare the diagram taken from that article with the diagram on page 40 of the booklet.
There are two obvious differences - the absence of the essential explanation in the booklet, and a completely different base sequence. For some reason, the author of the CIE booklet has converted all the bases in the original diagram into their complementary bases. It is always dangerous to rely on a single source, however reliable (such as Scientific American). The following diagram comes from an information site for the Human Genome Project, and confirms the information from Scientific American.
If the author has a valid reason for switching the bases in the booklet (and I can't see what that reason might be), then at the very least, he should explain the reason and point out the conflict with other sources. Page 144 This is supposed to be a specimen question for the Chemistry of Life section, which is why I have included it here. I don't know how the author has the nerve to include (a) part (ii). His diagrams of an alpha helix and a beta pleated sheet on page 12 are virtually impossible to understand. If he isn't capable of producing simplified diagrams of these, why should he expect students to do it? There is nothing wrong with the question - the author simply hasn't given his readers the tools to answer it. The graph question in (c) part (i) is very strange. Supposedly candidates are being asked to draw a graph, but then not do anything with it. What is the point? Even in the very early stages of chemistry, you would always expect to derive some information from a graph - otherwise you are just testing a fairly low-level mathematical skill. Given the shortage of specimen material for the new syllabus, it isn't helpful to waste the opportunity to generate a proper question instead of this non-question. Problems with Section 2: Applications of Analytical Chemistry All I have looked at in this section is the material on chromatography, and didn't spend a lot of time on it. My thanks to Eric Green and others for pointing out a number of other mistakes. Page 58 The relative abundance of Cl-37 is wrong. It needs to be 24.2% in order for the two figures to add to 100%. Pages 68 - 69 Compare the positions of the 1H peak and the 2H peak in the diagram on page 68 with what is said in the explanation on page 69. In the diagram, the 1H peak is at about 3.1; the explanation says 4.5. In the diagram, the 2H peak is at 4.5; the explanation says 4.3. The position of the shift for -OH groups is quite variable (a reliable web source of the NMR spectrum of this compound gave it at 2.3). But there should at least be consistency between diagram and the text! The spectrum on page 69 also has no labelling for relative abundance which means that you can't easily tie it to the explanation. Page 71 In the bottom diagrams on this page, the wording underneath the diagram talks about "d", the diagram uses "a". Page 71 This section on X-ray crystallography was pointed out to me by someone else as difficult to follow. As someone who knows absolutely nothing about x-ray crystallography, I totally agree. The section is complicated, and gives no indication of what a student actually needs to know - and this is supposed to be a "Support Booklet". In fact, all the syllabus says is "show awareness of the use of NMR and X-ray crystallography in determining the structure of macromolecules and in understanding their function". The interpretation stuff for NMR is described in another syllabus statement; there is no other statement on X-ray crystallography. Neither could I find any mention of it in the past papers I have access to. Concentrate on the syllabus phrase "show awareness". That should imply no detail whatsoever. Page 82 In Example 2, the wrong symbol has been used for the partition coefficient in both parts of the calculation - i.e. Ksp rather than Kpc. In the second extraction, an x has sneaked into the expression (0.67-x)/100 instead of a y. Page 83 The diagram here is wrongly labelled. It should be talking about an extraction using hexane, but it was obviously copied from somewhere else without changing all the labelling properly. The two references to "ether" on the diagram should both be replaced by "hexane". "Solution of S" is also slightly mysterious because there is no mention of S in the text that I can spot. It isn't at all easy to understand how this all works. You are trying to extract S from solution in water, and would start off with the solution in the vertical tube. The flask at the left would have pure hexane. If you heat that, it will boil and condense in the condenser at top right, and drip down onto the solution. You would then get partition of the S between the hexane and water. Some of the solution in the hexane will eventually overflow back into the flask. When that reboils, the non-volatile S will remain in the flask, and the hexane recycles through the system. Eventually all the S will be extracted from the water and end up in solution in the hexane in the flask. You will then have to separate the S from the hexane, presumably by distilling off the hexane. Pages 84 and 87 In the section on "The basic principles and techniques", the author uses the word "partition", and repeats it again in the third paragraph on page 87. I think this is potentially confusing to students and should have been avoided. The problem is that there are two different uses of the word "partition". In the text, the author is using the word in the sense of "separation". The solute separates into two parts - one of which stays in the moving phase, and the other part transfers to the stationary phase. In the diagrams on page 84, however, he is using the term "partition" in a different sense. In chemistry, the term "partition" is normally used for a division of a solute between two immiscible solvents. (There is actually a "partition coefficient" which measures how much of a solute you would expect to find in the two solvents under equilibrium conditions.) In these diagrams, he quite correctly distinguishes between "separation by partition" and "separation by adsorption". However, if you were to take what he says in the text literally, both of these would have to count as separation by partition - that's silly! To use different meanings of the same word within a few lines of each other is bound to be confusing! This problem would disappear completely if he had chosen a different word in the text. Page 85 4 - 5 lines under the diagram, it says ". . . place the paper in a beaker with a few iodide crystals." It means iodine crystals. This looks a fairly minor mistake, but if a student wrote this in an exam, I would hope that they would lose a mark. Page 90 Two problems here - one minor one, and one bigger one. In the sixth line under the diagrams, he talks about a "20 cm3 column". This should, of course, be a "20 cm column". More importantly, the whole basis of the calculation is flawed. The internal volume of the column available to the liquid isn't going to be anything like 2.5 cm3. The column is packed with "tightly packed small particles of the stationary phase". That means that there will be far less than 2.5 cm3 of liquid in the column at any one time. Because there is no way of actually finding out the real volume of liquid in the column, the whole calculation becomes pointless! Problems with Section 3: Materials and Design So far, I haven't looked at this section at all. What can you do about this? There are two things that you can do about this: help to add to this list of problems so that everybody using the booklet can be aware of them, and then complain to CIE. Adding to the list If you are a teacher and have found other things wrong with the booklet (either mistakes or places where the explanation is difficult to follow either for yourself or your students), could you contact me at the address on the about this site page. If the mistake isn't fairly obvious, could you explain exactly what the problem is and preferably point me at a source (or sources) that I can quote for a correct version. If you are a student and think you have found a mistake or find something difficult to understand, please discuss it first with your teacher and ask them to contact me if they agree that something is wrong. I can't cope with e-mails from potentially tens of thousands of students! If you are a student, please don't write to me! Talk to your teacher so that you can be sure that there is a problem, and then write to CIE instead. Complaining to CIE If one person complains to CIE about this booklet, they will probably take no notice. If thousands of people complain, perhaps it might make a difference. If you feel let down by this booklet because of the mistakes that it contains or the poor explanations, e-mail CIE and tell them, and ask them what they intend to do to put it right. Some guidance on doing this:
Keep an eye on this page I will update this page as people point out other difficulties to me, but I probably shan't say that I have done this on the Latest Additions section of the Main Menu - I can see it happening so often that it will clutter that section up. As you are going through the syllabus, keep checking to see if there is anything here about the pages you are working on. Return to questions list . . . © Jim Clark 2007 |
