Questions on Alkenes
1. State the equation and name the organic product when propene reacts with:
(a) hydrogen using a nickel catalyst at 180 oC.
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(b) chlorine gas in the absence of water.
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2. Describe how you could distinguish practically between hexane and hex-3-ene by using a simple
chemical reaction. Describe what you would observe in each case and state any relevant equations and
name any products formed.
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3. Ethanol is increasingly being produced commercially by the fermentation of crops in order to use as a
biofuel in place of/in addition to gasoline (petrol). This is ecologically friendly in terms of greenhouse gas
emissions but it is using up vast areas of land which could be used for food production.
Ethanol can also be made industrially by the hydration of ethene. State the equation for the hydration of
ethene.
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4. (a) State the equation and name the organic product when but-2-ene reacts with hydrogen iodide.
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(b) Unlike the reaction with but-2-ene, the reaction of but-1-ene with hydrogen iodide is not on the IB
Core. This is because in theory it can give two different organic products although in practice only one of
them is formed. Deduce the identity of the two possible products.
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5. (a) Draw the structure of the repeating unit of poly(chlorethene).
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(b) Deduce the structure of the repeating unit of poly(tetrafluoroethene).
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(c) Poly(tetrafluoroethene) is also known as ‘Teflon’ or ‘non-stick’ and it is used to make artificial joints
for humans as well as coat frying pans. Suggest a reason why it is so unreactive.
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Answers
1. (a) CH3CH=CH2(g) + H2(g) → CH3CH2CH3(g) Product: propane
(b) CH3CH=CH2(g) + Cl2(g) → CH3CHClCH2Cl(l) Product: 1,2-dichloropropane
2. Add a small amount of bromine water to each substance. The bromine will dissolve in the hexane to
form a yellow-brown solution but no reaction takes place. The hex-3-ene solution will decolourise the
bromine water. This is due to the addition of the bromine water to the double bond of the hex-3-ene to
form 4-bromohexan-3-ol.
CH3CH2CH=CHCH2CH3(l) + Br2(aq) + H2O(l) → CH3CH2CHBrCH(OH)CH2CH3(l) + HBr(aq)
(The IB would also accept 3,4-dibromohexane, CH3CH2CHBrCHBrCH2CH3, as the product as this would be
formed if no water is present).
3. H2C=CH2(g) + H2O(g) → C2H5OH(l)
4. (a) CH3CH=CHCH3(g) + HI(g) → CH3CHICH2CH3(l)
Product: 2-iodobutane
(b) 1-iodobutane, CH2ICH2CH2CH3
and 2-iodobutane, CH3CHICH2CH3
5. (a) ―(―CH2―CHCl―)n―
(b) ―(―CF2―CF2―)n―
(c) The very strong C-F bond is difficult to break
or the structure is such that there is no room around each carbon atom for other atoms to approach.