Ethanol is an alcohol used in alcoholic drinks and as a fuel. When ethanol burns completely in oxygen, it produces carbon dioxide and water. Ethanol can also react with sodium metal. Describe what you would observe when a small piece of sodium is added to ethanol, and explain why ethanol is classified as an alcohol rather than a haloalkane.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Ethanol has the molecular formula C₂H₅OH. Haloalkanes contain a halogen atom bonded to a carbon chain, for example chloroethane (C₂H₅Cl).
Model answer (5 marks)
When a small piece of sodium is added to ethanol, the sodium reacts with the –OH group and the surface of the metal is covered by a thin film of sodium hydroxide. The reaction releases hydrogen gas, so bubbles/fizzing are seen and the sodium gradually disappears.
Ethanol is classified as an alcohol because it contains a hydroxyl (–OH) functional group attached to a carbon chain. Haloalkanes, by contrast, have a halogen atom (F, Cl, Br or I) bonded to a carbon chain and no –OH group. Since ethanol has an –OH and no halogen, it is not a haloalkane.
Ethanol is classified as an alcohol because it contains a hydroxyl (–OH) functional group attached to a carbon chain. Haloalkanes, by contrast, have a halogen atom (F, Cl, Br or I) bonded to a carbon chain and no –OH group. Since ethanol has an –OH and no halogen, it is not a haloalkane.
Examiner tips
- Mention the fizzing and disappearance of sodium to gain the reaction observation marks.
- State the –OH group to justify the alcohol classification and the absence of halogen for the haloalkane comparison.
Common mistakes
- Writing that ethanol reacts with sodium to give sodium chloride instead of hydrogen gas.
- Failing to mention the –OH group or the lack of a halogen when explaining the classification.
Mark scheme (5 marks)
- Sodium reacts with ethanol and bubbles/fizzing is observed
- The sodium gradually disappears / gets smaller
- The gas produced is hydrogen
- Ethanol contains an –OH (hydroxyl) functional group bonded to a carbon chain
- Haloalkanes contain a halogen atom (F, Cl, Br or I) instead of –OH, so ethanol does not contain a halogen and therefore is not a haloalkane
Key terms in this question
Related
- All OCR A-Level Chemistry B: Salters (H433) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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