Recent Posts by David Allen

Hydrogen

By Wednesday, July 10, 2019 No tags 0

We are currently having a space themed week in school to celebrate the 50th anniversary of the moon landings. not quite the 50th anniversary, more like 49 and 49/50ths (Armstrong walked on the lunar surface on the 16th July 1969) but as we break up on Friday it was the best the school could do. The students have a few days off timetable and are engaged in many different activities that relate to the moon landings. In chemistry, I guess we have ...

Equilibria part 2

By Monday, July 8, 2019 No tags 0

Last month I ran over the basics of equilibria. The rationale for this was that I felt that it was a part of the course that had been poorly answered in the recent IB May examinations. I do need to stress that this is my own personal opinion and not that of the IB. This month I will run over the more difficult concepts associated with equilibrium, Le Chatelier’s principle. Le Chateliers principle allows you to determine what happens to a system ...

Forwards, backwards, left or right? – Equilibria Part 1

By Friday, July 5, 2019 No tags 0

There were a few questions on equilibria in this year’s May exams. As a teacher I felt that students didn’t perform very well on these questions (I have no evidence for this apart from conversations with a very small number of students who sat the exams) so thought that this month may be an opportunity to help reinforce and summarise some of the concepts covered. First of all, what do we mean by equilibrium? A reaction that is at equilibrium doesn’t ...

Chernobyl

By Monday, July 1, 2019 No tags 0

I’m half way through watching the new HBO / Sky miniseries Chernobyl. Have you seen it? Here in the UK it has received some great reviews with some critics claiming it is the best TV series ever produced. Chernobyl, as you probably know was a nuclear power station in the Ukraine that exploded with catastrophic consequences in 1986. If you study option C, Energy you will look at nuclear fission and fusion in section C3. Chernobyl was a fission reaction. In a ...

Using Catalysts in Lab Work – a Slightly Different Approach

By Friday, June 28, 2019 No tags 0

I imagine that, as teachers, we all carry out a hydrogen peroxide decomposition using manganese dioxide. We may also demo cracking where we use aluminium oxide or silicon oxide as a catalyst. This aside, do we really make much use of catalysts in our lab work? https://www.youtube.com/watch?v=p5qvi20J5IM The other day I was carrying out a lab with my students that involved collecting hydrogen by upwards displacement of water, using magnesium and hydrochloric acid. We are also fortunate to have a fantastic lab ...

Get it right – Electrochemical Cells

By Wednesday, June 26, 2019 No tags 0

This aim if this blog post is to equip you with an aid memoir – something you can copy, paste, edit and print out to aid your revision. The reasoning behind this post is from my experience as an examiner. In my opinion (and this may not be one shared by the IB) students tend to answer questions on electrochemical cells quite poorly. This is possibly due to the topic being one of the last topics to be taught – maybe ...

Caffeine

We all love our caffeine hit in the morning, but what is this magic ‘energy’ giving substance and is it actually good for us? The IUPAC name for caffeine is 1,3,7-Trimethylpurine-2,6-dione and the molecule has the following structure: By Vaccinationist - Own work, based on PubChem, Public Domain, https://commons.wikimedia.org/w/index.php?curid=54417143 Interestingly, you may notice that the structure is similar to adenosine and guanine (DNA purine bases) – the clue comes from the name. Caffeine is a psychoactive drug, which puts it in the same group ...

Colorimetry

I love carrying out colorimetry, it is one of my favorite types of labs to carry out and I do believe that as teachers, it is a really underused type of lab and undervalued type of lab. I always teach the theory first, covering the ideas behind the Beer-Lambert Law and the way that a colorimeter works. We will usually start off by getting the class to make up standard solutions of copper sulfate (0.1 mol dm-3 to 1.0 mol dm-3 ...

How do you do it?

Personally, I find section 9.2 one of the hardest parts of the course to teach. It relates to voltaic cells. I can never remember is it left minus right or vice versa, which side is positive, which is negative? In order to help teach this I put together a useful set of ideas / principles that I now use to help my teaching. It does involve some learning / memorization of facts but once these points are learnt, everything else ...

Sigma, Pi, Hybridization and Shape

Sigma bonds, Pi bonds. Shapes of molecules. Hybrid orbitals. How do they all fit together? I was really confused with this information when I was a student. It wasn’t covered when I did my biochemistry degree and I only felt like I really understood things until I started teaching about the concepts … so I really hope this blog post helps your understanding of things. Where do I start? Well, the three above concepts (Sigma & Pi, shape and hybrid orbitals) are, in my ...

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