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7
7 Ethanol, C₂H₅OH, is a colourless liquid that mixes completely with water. The diagram shows the structure of an ethanol molecule.
(a) Explain why ethanol is soluble in water. [2]
(b) Ethanol is also used as a fuel. Write the balanced equation for the complete combustion of ethanol. [2]
Detailed explanationQ7
Answer
Ethanol has an –OH group. The O–H bond is polar, so ethanol molecules form hydrogen bonds with water molecules.
Dashed line: hydrogen bond between ethanol and water
These attractions are about as strong as the ones between water molecules, so the two liquids mix completely.
Tick the marks you earned.
Score 0 / 2
Common slip: writing "ethanol is polar so it dissolves" earns nothing. Name the –OH group and the hydrogen bonds to water.
Also avoid: saying it forms covalent bonds with water. Those are intermolecular attractions, not bonds inside the molecule.
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