Recent Posts by David Allen

What Is Entropy?

Entropy is covered in the AHL part of the course: Topic 15.1 in the energetics / thermochemistry unit. The entropy change (symbol = S) in a chemical reaction is determined by as follows: total entropy change = total entropy of products – total entropy of the reactants You will have probably been taught that entropy is a measure of disorder. Order goes to disorder. The universe is expanding (and therefore getting more disordered). Liquid water has a greater entropy than solid water (ice) ...

Benzene

Benzene is sometimes referred to as an aromatic compound as opposed to the majority of other organic molecules that you have so far studied that are found in chains and sometimes referred to as aliphatic compounds. Aromatic substances are said to have an unsaturated ring of atoms whereas aliphatic substances open chains. The word ‘arene’ is sometimes used in place of aromatic. Benzene has the formula C6H6. Its structure was first proposed by the German chemist Friedrich August Kekulé in 1865. Its ...

The Avogadro Project

This sounds like some sort of clandestine secret government project I think but in fact, it is something far more interesting! The Avogadro projects earliest rumblings began in the 1990’s and were linked in with defining the kilogram. Its results were published in January 2011 and updated in 2015. The ultimate aim of the project was to provide the most accurate determination ever of the Avogadro constant. It involved an international collaboration of many scientists. As nearly all good IB students will ...

Nobel Prize in Chemistry and HL Biochemistry

This years Nobel prize in chemistry has been awarded to three researchers, Frances Arnold, George Smith and Gregory Winter for their work on enzyme research. Their work uses a technique called ‘directed evolution’ to create new enzymes. It does also tie in nicely with some of the subject material covered in the HL biochemistry option. As I understand it, the work involves causing a gene (in a bacteria) to mutate randomly by using chemical mutagens or a technique called PCR. The ...

Possible EE / IA project

By Wednesday, October 3, 2018 , , , 0

I’ve just stumbled upon a great article on the BBC website. The article can be found here: https://www.bbc.co.uk/news/science-environment-45398434 The article is about a group of plants that have evolved to take up toxic metal ions into their systems. The metals in question are nickel and zinc and usually, these ions would be toxic to plants, even in relatively small concentrations. Plants that have this ability are referred to as hyperaccumulators. One tree in particular, the rare Pycnandra acuminate produces a latex that is ...

Energy Levels

I’ve just finished teaching this topic to my students. I always find it an interesting topic to teach as the ideas used are so different to those you are probably taught prior to IB. Just when you were happy with the idea that atoms have electrons in shells you suddenly get told that this is not the case and that you need to know and use another model of the atom. It’s a great example of a paradigm shift (you will ...

Everyday Life, Benzyl Alcohol and the EE

In my experience, the biggest problem students have with EE's is picking the right thing to investigate. Students will tell me they want to carry out an EE in chemistry and have no idea what they will investigate. Those that do have ideas quite often have ideas that are too simple or too difficult, never ‘just right’. Because of this, I would strongly encourage you to tell your students to keep their eyes open and look for an EE in ...

Dyes

I’ve just finished my summer reading book, Ken Follett’s novel World Without End. If you haven’t read it, I would thoroughly recommend it, although it is the second book of a trilogy (book 1 is called The Pillars of the Earth). The book I sent in the thirteenth century in the fictional city of Kingsbridge in the UK (although there is a Kingsbridge in the UK, the Kingsbridge in the book is not this town) and revolves around the Black Death. ...

Vitamin Chemistry

Vitamins are taught in the biochemistry option. However, the aim of this blog post is not to cover the exact requirements of the IB course. Instead, my intention is to give the reader an overview of the topic. So, what do we mean by vitamins? Well, vitamins are organic molecules that are needed in small quantitates in order for an organism to remain healthy. If an organism is lacking in a particular vitamin it will develop a deficiency disease. Vitamins will vary ...

The Biochemistry Option

Proteins Proteins are a group of biomolecules (or biopolymers) that form enzymes and muscles in the body. They are the chief nitrogenous compounds found in living organisms but are still only approximately 15% nitrogen. The other elements they are comprised of is carbon, oxygen, hydrogen and a relatively small amount of sulphur. Proteins are made of amino acids which, as the name implies, are made from amino groups (NH2) and carboxylic acid groups (COOH). These groups are joined together via a carbon ...

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