AQA · Chemistry · 8462
GCSE Chemistry (AQA): Reaction of Alkenes
Topic 7 — Organic Chemistry. Generated from the caption track of Cognito's lesson video "GCSE Chemistry - Addition Reactions of Alkenes"; each card deep-links to the moment in the video it came from. Lesson 7.09 of Cognito's AQA GCSE Chemistry (Triple) course (Higher tier), filed under AQA Chemistry 8462. Teaching by Cognito — https://cognitoedu.org/coursesubtopic/c2-gcse-aqa-h-t_7.09.
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How is unreacted ethene separated from the ethanol and water mixture?
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By cooling the mixture: ethene has a low boiling point so it stays a gas while ethanol and water condense.
Why can alkenes undergo addition reactions?
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Their carbon-carbon double bond can open up, freeing both carbons to bond to atoms from another molecule.
What is the functional group of alkenes?
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The carbon-carbon double bond (C=C).
What is formed when propene reacts with hydrogen over a catalyst?
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Propane — the double bond breaks and hydrogen atoms bond to the two carbons, giving a saturated alkane.
What is the chemical test to distinguish an alkene from an alkane?
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Add bromine water: an alkene decolourises it from orange to colourless, an alkane leaves it orange.
Alkenes are classed as ? hydrocarbons because they contain a C=C double bond.
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unsaturated
Which technique separates ethanol from water after the hydration of ethene?
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Fractional distillation — ethanol boils first because it has the lower boiling point.
What is formed when ethene reacts with bromine?
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Dibromoethane, and the orange bromine colour disappears.
Why is the product of adding hydrogen to an alkene classed as an alkane?
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The C=C double bond has been broken, so the molecule is saturated.
Why does bromine water stay orange when added to an alkane?
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Alkanes are saturated — with no C=C double bond, there is nothing for the bromine to add across.
What product forms when ethene reacts with steam?
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Ethanol — the water splits into H and OH, which bond to the two carbons.
What conditions are needed for the reaction of ethene with water?
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A catalyst and a high temperature, so the water is present as steam.
How does the reaction of alkenes with halogens differ in conditions from the reaction with hydrogen?
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The halogen addition needs no catalyst.
Because it contains an OH group, ethanol belongs to the homologous series called the ?.
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alcohols
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