Preparation of an organic liquid

All specifications aimed at learners 16–18 years include some form of synthesis of a pure organic liquid or solid. Learners will need to appreciate that organic synthesis can involve multiple reactions, followed by extraction and purification steps. 

Chapter titles: 00:10 Introduction and overview; 01:08 Preparation: combining concentrated hydrochloric acid with 2-methylpropan-2-ol; 02:07 Separation: removing the aqueous layer using a separating funnel; 03:10 Purification: first, sodium hydrogen carbonate solution is added to remove unreacted hydrochloric acid; 04:43 Then solid anhydrous sodium sulfate (drying agent) is added to remove any trace amounts of water; 05:25 Finally, distillation separates the sample from any remaining reactant.

Teacher notes

Full teacher notes are available in the supporting resources booklet, including ideas for how to use this video and the supporting resources as part of your teaching. 

This practical takes learners through the stages of preparation, separation and purification of an organic liquid. The whole purification process is generally more complex and involved than the preparation in the first place and learners should understand why the idea of purification is so important when creating chemical compounds – link to real-world examples such as preparation of medicines.

There are multiple steps involved in this practical providing a good opportunity for learners to practice a number of experimental techniques and procedures. Help them to make links to different situations and processes where the same techniques are used, eg a separating funnel is used whenever we have two immiscible liquids we want to separate.

With multistep experiments, it’s easy for students to follow instructions unthinkingly without pausing to appreciate the underlying chemistry behind each step. Using the video as support will help learners feel more confident with the procedures and gain a better understanding of the reason for each task before they carry out the live practical – this will help them focus on the skills and develop understanding when they get to it.

Technician notes including the equipment list and safety notes are provided. If you are planning to carry out the practical in the classroom, you will need to carry out your own risk assessment.

Further practical activities and other resources

Complete the process by testing the organic sample for purity using thin layer chromatography.

A related experiment based on preparation of an organic solid is shown in our Aspirin screen experiment – an interactive experiment to walk students through the experimental process before they try it out in the lab.

Prior knowledge

The video and resources assume the following prior knowledge:

• Nucleophilic substitution reaction of alcohols.
• Separation technique: separating funnel used for immiscible liquids – polar/non-polar solute and solvents – organic haloalkane will not bond with aqueous solvent, therefore separating funnel can be used.
• Often reagents used are either acidic or alkaline and that neutralisation is an important step after the product is made to neutralise any unreacted reagent.
• Distillation as a separation technique when the product we are interested in has a different boiling temperature to the other compounds in the mixture.
• How to complete a TLC chromatography test (if learners have only done paper chromatography use this as the base with some additional teaching at the time).

Common misconceptions

Be aware of misconceptions learners may have around this practical, for example:

• Purity in chemistry is not the same as purity in other contexts. A pure element or compound contains only one substance, with no other substances mixed in. So pure water in chemical terms is H₂O molecules with nothing mixed in. This is unlike the ‘real-world’ view of pure water, often meaning water from a tap or mountain spring – these water samples will contain dissolved minerals, so are not chemically pure.
• Not understanding the need for purification. With a liquid the visible different layers help to introduce the need to separate the product, but impurities remain even when layers are no longer visible – as demonstrated in the later steps of this practical. This misconception can be more of a problem with an organic solid as the crude product formed appears to be a pure substance although it contains impurities that need to be removed. It is worth going into what and why impurities can occur in the first place to avoid rote learning of the phrase ‘to remove impurities’ without understanding what these actually are.
• Learners can struggle to realise that each technique has a purpose and can therefore be used in various synthetic routes – these techniques are not limited to this practical only. To combat this, focus on the rationale behind why each technique is used and discourage learners from copying mechanical processes without understanding why they are doing each step.