Recent Posts by David Allen

Superacids

The concept of superacids was a new on to me until the other day when I read about a chemistry competition that had been held in Moscow earlier this summer. You may have been in this very competition so, if you had, and I get something wrong, please do put me right! The competition asked students to 'design' (on paper) an alien blood that resembled the blood in the 'Alien' movies. If you recall, this blood needed to be capable of ...

Teaching Equilibrium

I've just taught this topic and thought it was worth sharing my ideas as to how I introduced the topic and concept of equilibrium. Firstly, something worth considering before you launch into the topic is when do you teach it? In my opinion it needs to go after energetics. This is because some of the concepts need a good understanding of exothermic and endothermic reactions before one can decide on the effect of temperature on the position of equilibrium. It could ...

An Introduction to Equilibria

Equilibria can be a tricky concept to understand. In order to understand it, you need a good idea of reversible reactions and then a good idea of a dynamic equilibria. So, what is a reversible reaction? Put simply, it is a reaction in which products can be turned into reactants, but reactants can also be turned back into products. This can be shown using the ⇌ symbol: Reactants ⇌ Products For example, ammonium chloride will thermally decompose into ammonia and hydrogen chloride gases, but these gases will ...

Collision theory and mechanisms – linking it together

I’ve just started teaching the kinetics topic to my students and so far we have focussed on the collision theory. Have you heard of this? The collision theory explains to us what happens during chemical reactions in terms of the collision of particles. In order for a chemical reaction to occur, particles need to come together (collide) with sufficient energy (speed). This is called the activation energy (and is defined as the minimum amount of energy required for a chemical reaction). If ...

Making esters

We carried out a great lab in school today, making esters. Have you ever done this? What was good about it was that we used a good range of reagents and got some very different results. I set the class up with a range of alcohols and carboxylic acids and told them it was up to them what they wanted to make. We used microscale quantities for two important reasons: 1, As a safety precaution The beauty of using the microscale quantities is that ...

Teaching optical isomers

I've just started to teach this topic to my students. It doesn't take too long but I do find it an enjoyable topic to teach. But how do you teach it? I always warn the students that the topic is jargon heavy - the words / phrases used in the topic such as  chiral, racemic, racemate, optically active are all pretty specific to optical isomers and are not used outside of the topic. In my teaching I have found that students understand the ...

Optical isomerism

Optical isomers are hard to conceptualise. They are molecules with the same molecular formula and structural formula. They look exactly the same both on paper and in the real world. However, they only exist in pairs, it is only possible to get two optical isomers of the same molecule which makes things a bit easier to deal with (it should be notes that a molecule such as C5H12 has three isomers - not optical isomers but structural isomers, namely pentane, 2 methylbutane ...

Putting your course together

This blog post is primarily aimed at teachers new to the course …. But that said, even if you are an experienced teacher it is always worth reviewing how you do things. There are always lots of things to consider when setting up the course. Do you teach by yourself or do you share your group with another teacher? First things first I’m aiming this blog post at teachers who teach a class by themselves as in my experience, this seems to ...

Gas Volumes

I have written this blog post with all you new first year IB students in mind. If you have started the course recently (or about to start the course very soon) it is likely that the first or second topic that you study will be ‘Stoichiometric relationships’, which is just a posh way of saying ‘moles’. That said, if you are an old hand, a second year IB student don’t stop reading! This blog post contains some important revision for ...

Limiting reagents

Limiting reagents is a concept that is easy to understand in one context... but tricky to understand in another. Before I expand on this statement, what do I mean by limiting reagents? Well, unless you have some super precise mass balances, when carrying out a chemical reaction you will always add too many atoms / molecules / particles of one substance and not enough of the other. The one that you have added too much of is the reagent that is ...

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