Using Catalysts in Lab Work – a Slightly Different Approach

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?

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 technician who reads around some of the labs we order from her. She found a slightly better way of generating the hydrogen using zinc granules and hydrochloric acid. The problem with hydrochloric acid and magnesium is that the reaction is over very quickly. We were needing a sustained way of collecting hydrogen – speed was not too important.

What’s all this got to do with catalysts? Well, the zinc / hydrochloric acid method uses a few drops of copper sulfate (Cu2+ ions to be specific) to catalyse the reaction. And it does work quite noticeably (I tried to generate hydrogen with and without the catalyst).

This got me thinking and reaching for one of my favourite demo books ‘Classic Chemistry Demonstrations’ by the Royal Society of Chemistry (ISBN:
978-1-87034-338-1),

If you don’t have this book – it is well worth investing in. Except don’t try experiment 30, the non-burning £5 note if you have a new polymer note as it will melt – much to my horror… But I digress).

I could remember a few years ago putting together a lesson on catalysis and after a bit of digging around I found the lab. It was still catalysing the decomposition of hydrogen peroxide, but also involved using (as well as manganese dioxide) lead (iv) oxide and iron (iii) oxide.

The book also covers using ammonium molybdate (vi) to catalyse the reaction between hydrogen peroxide and sodium thiosulfate and using copper (ii) oxide, manganese dioxide, iron (ii) oxide and silica oxide.

Naturally, I have omitted practical details and it goes without saying that if you carry out any lab work that you are responsible for any risk assessment and health and safety checks that need to be carried out.

I have a question to end with. Generally, transition metals are good catalysts. Now I may be wrong but I thought this was because they had partially filled d orbitals that could ‘temporarily’ accept electrons. In this post, silica has popped up twice, but this does not have d orbitals. Is anybody body able to help or explain?

Until next time…