To illustrate the differences in reactivity of isomeric alcohols, try using the iodoform demonstration in the video. Follow the discussion scenario in sequence for tips to help your students understand a difficult concept in carbon chemistry.
This is an effective practical procedure to illustrate how simple chemical tests can distinguish between primary, secondary and tertiary alcohols. One of the tests is the iodoform reaction, which has not been on examination specifications for a while. We’ve made this video in case you’re not familiar with it.
What are the merits of doing the practical first to establish theoretical concepts, or doing the theory first so that the practical makes sense?
Have you considered doing the practical on a microscale to save on chemicals and increase safety?
The iodoform reaction is relevant to aldehydes and ketones, but this resource suggests it’s all about alcohols – so when would it be used?
- The title of the resource could be a little misleading because students would ideally need to have covered aldehydes and ketones if they’re going to appreciate the significance of the iodoform reaction. This is usually taught after they’ve been introduced to alcohols. It would be a good way for them to revise the relationship of alcohols to aldehydes and ketones.
- The iodoform reaction has not been on examination specifications for a few years now; that just means students don’t need to answer exam questions on it. It’s still an interesting reaction.
What other related practicals are there?
- There are other characteristic reactions which aldehydes and/or ketones undergo; this exercise could form an introduction to these. Common examples are the silver mirror test (using Tollen’s reagent), Fehling’s test, and the reaction with acidified 2,4-dinitrophenylhydrazine (Brady’s reagent).
What is special about the iodoform reaction?
- It’s a reaction in which iodoform (or triiodomethane, to use its systematic name), a yellow crystalline product, is formed in the presence of certain compounds. Basically these are ethanal, any methyl ketones or their alcohol precursors. The first two of these contain the acetyl group, CH3C=O.
How could we approach this practical to maximise engagement?
- This depends on what students already know and understand. For example, if they have good theoretical knowledge already, you could make this a task in which the three alcohols are not labelled and they have to identify which is which.
Could we do this as a demonstration instead?
- If students are less confident with handling chemicals and equipment then doing this as a demonstration would be a good idea. Showing them the two different reactions first, performed by you as the expert, would be good modelling of skills. Demonstrations like this also save time and chemicals.
The resource says a risk assessment is required – what exactly does this involve?
- Risk assessment basically consists of three steps: identify the hazards, consider the risk of them causing harm, and if necessary take action to minimise this risk. Although the quantities used in these reactions are small, there is a risk of damage to eyes from some of the chemicals, in particular 2 mol.dm–3 sodium hydroxide solution.
Sign up to our Carbon chemistry online CPD course for over 132 different videos, discussions and exercises like this.
The course has 12 topics from Representing organic structures to Substitution and Addition reactions and will take approximately 12 hours to complete.
The Carbon chemistry course explores how to teach about the special nature of carbon, some of the important classes of compounds it forms, and their most important reactions. It will help you to help your students understand how the complexity of these compounds leads to variation in molecular structures and spatial arrangements of atoms – the topic of isomerism – and how we can use a variety of methods to find out more about these structures.
After working through this course you will be able to:
- confidently teach about the key aspects of carbon chemistry.
- help students understand and represent structures of carbon compounds;
- confidently teach students about functional groups, their main specific reactions and the principles that govern reactions involving carbon compounds;
- help students explain the factors that lead to variation in the physical properties of carbon compounds;
- confidently teach about organic synthesis and methods for determining the structures of carbon compounds.
You can find further details about the structure of the course in the additional information below. Visit our teacher CPD pages to view our other courses.
Thank you to John Walker and Tim Jolliff for authoring this course.