7.6 Alkenes and their reactions
6 exam questions worth 10 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
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What is the formula of butene?
Choose one answer.
Correct Not quite: the answer is C4H8
Mark scheme
C
Model answer
C: alkenes are CnH2n, so butene (4 carbons) is C4H8.
Name the product when propene reacts with hydrogen, and state the catalyst used.
Mark scheme
- propane (1)
- nickel (1)
Model answer
Propane forms, using a nickel catalyst.
Write a balanced equation for the reaction of ethene with steam, and name the product.
Mark scheme
- C2H4 + H2O → C2H5OH (1)
- ethanol (1)
Model answer
C2H4 + H2O → C2H5OH; the product is ethanol.
Describe a test to show that a hydrocarbon is unsaturated. Give the result.
Mark scheme
- add / shake with bromine water (1)
- turns from orange to colourless (1)
Model answer
Shake with bromine water; an unsaturated hydrocarbon decolourises it from orange to colourless.
Explain why alkenes often burn with a smoky flame.
Mark scheme
- incomplete combustion (1)
- not enough oxygen, so unburnt carbon (soot) forms (1)
Model answer
Alkenes often undergo incomplete combustion, so some carbon is released as soot, making the flame smoky.
What is meant by an addition reaction?
Mark scheme
- atoms add across the double bond to form a single product (1)
Model answer
A reaction in which atoms add across the C=C double bond, giving one product.
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