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CP5 investigates ethanol oxidation. Ethanol can form ethanal and, with further oxidation, ethanoic acid. In an approved controlled-oxidation preparation, removing volatile ethanal by distillation as it forms limits its exposure to oxidant. Reflux instead returns condensed vapour and allows more prolonged oxidation. Use the specific reactants, addition sequence and heating procedure provided by the laboratory.
Video by Royal Society of Chemistry. The demonstration uses ester preparation to show distillation apparatus. This lesson applies the technique to removing a reaction product; your teacher’s reaction and conditions take precedence.
Viewing focus: Distinguish ethanol oxidation to ethanal and ethanoic acid
After watching, attempt these questions before opening the answers. You can also use the written lesson below.
After watching 1: Why does condenser water normally enter at the bottom?
To keep the cooling jacket full. Water displaces air upward as it fills the jacket.
After watching 2: Where should the thermometer bulb measure temperature?
In the vapour path near the condenser entrance. This measures the vapour being collected.
What you'll be able to do
CP5 investigates ethanol oxidation. Ethanol can form ethanal and, with further oxidation, ethanoic acid. In an approved controlled-oxidation preparation, removing volatile ethanal by distillation as it forms limits its exposure to oxidant. Reflux instead returns condensed vapour and allows more prolonged oxidation. Use the specific reactants, addition sequence and heating procedure provided by the laboratory.
A distillation assembly has a heated reaction vessel, a still head and thermometer, a downward condenser and an open receiving arrangement. The thermometer bulb should measure vapour entering the condenser near the side-arm, rather than the liquid temperature far below it. The apparatus must not become a sealed, heated system. Use the laboratory’s controlled addition and heating procedure for oxidants and volatile organic compounds.
Cooling water enters the lower condenser connection and leaves the upper connection so the jacket fills, giving effective cooling. Clamp glassware securely without straining joints. Add anti-bumping granules before heating where specified; never add them to an already hot or boiling liquid. Use approved electrical heating or a water bath when flammable vapours exclude a naked flame.
Collect the specified temperature fraction and record what is actually observed. A rapid heating rate can cause carry-over and poor separation. Losses occur from incomplete condensation, transfers and material left in apparatus. A fraction is not automatically pure just because it was distilled: compounds with similar boiling points may be collected together.
Use the limiting reagent and reaction ratio to calculate a theoretical amount, then compare with the isolated product. A low yield may reflect incomplete conversion, further oxidation or physical loss. Infrared evidence such as a carbonyl absorption with no broad carboxylic-acid O–H band can support the intended product, but the complete spectrum and other evidence are needed to distinguish possible carbonyl compounds.
A boiling range is useful only when measured with the correct thermometer position and compared under appropriate pressure. Narrower collection can improve purity at the cost of recovered quantity. Explain that trade-off rather than claiming that every increase in yield is an improvement in product quality.
In shorthand, CH₃CH₂OH + [O] → CH₃CHO + H₂O and CH₃CHO + [O] → CH₃COOH. The overall conversion to acid uses two [O] equivalents. Acidified dichromate changes from orange to green when reduced, but that colour change alone does not establish which organic product was isolated.
An aldehyde test on a fresh product portion supports ethanal, while acid and spectroscopic evidence can support ethanoic acid. Explain why an apparently successful oxidation can still give the wrong desired stage if the aldehyde remains with oxidant. Record yield and identity separately; successful collection of a volatile liquid is not itself proof of ethanal purity.
Attempt these problems on paper before opening the worked reasoning. Explain your steps as well as giving a final answer.
Common mistakes to avoid
Key takeaways
Question 1: A learner uses reflux when the task aims to isolate a readily further-oxidised aldehyde. Explain the likely consequence.
Further oxidation to carboxylic acid is more likely; distilling the product as it forms limits that exposure.
Check the assessed scope and practical or mathematical requirements.
An external explanation or interactive activity to use alongside the lesson. It may include extension material.
Close the notes and answer from memory. Revisit any explanation you cannot yet reconstruct.
Test yourself
Answer a few questions, then review anything you missed.
Start with the quiz above to check the key ideas. You can also choose another topic from the practice library.