Alkenes (Edexcel IGCSE Science (Double Award): Chemistry): Flashcards
Exam code: 4SD0
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Define alkene.
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Define alkene.
An alkene is an unsaturated hydrocarbon that contains a carbon-carbon double bond (C=C) as its functional group.
The general formula for alkenes is ...........
The general formula for alkenes is CnH2n.
True or False?
Alkenes are classified as unsaturated hydrocarbons.
True.
Alkenes are unsaturated because they contain a C=C double bond, which means they can make more bonds with other atoms by opening up the double bond.
What is the functional group in all alkenes?
The functional group in all alkenes is the C=C double bond. This makes alkenes more reactive than alkanes because the double bond can open and allow other atoms to bond with the carbon atoms.
Ethene has the molecular formula .......... and propene has the molecular formula ...........
Ethene has the molecular formula C2H4 and propene has the molecular formula C3H6.
True or False?
Alkenes are more reactive than alkanes.
True.
Alkenes are more reactive than alkanes because the C=C double bond can break open to allow other atoms to join the molecule in addition reactions. Alkanes have only single bonds and cannot undergo addition reactions.
Define unsaturated (in the context of organic chemistry).
An unsaturated compound is one that contains at least one carbon-carbon double bond (C=C), meaning it can undergo addition reactions by opening the double bond to bond with more atoms.
Why are alkenes described as unsaturated hydrocarbons?
Alkenes are described as unsaturated hydrocarbons because they contain a C=C double bond. This means the carbon atoms are not bonded to the maximum number of hydrogen atoms possible. The double bond can open to allow more atoms to attach.
Define addition reaction (in the context of alkenes).
An addition reaction is a reaction in which atoms from a simple molecule add across the C=C double bond of an alkene, converting it into a single bond and producing a single product.
True or False?
When bromine reacts with ethene, a dibromoalkane is formed.
True.
Bromine adds across the C=C double bond of ethene in an addition reaction, forming 1,2-dibromoethane.
When bromine reacts with an alkene, bromine atoms add across the .......... bond to form a .......... alkane.
When bromine reacts with an alkene, bromine atoms add across the C=C bond to form a dibromoalkane.
What is the result of adding bromine water to an alkene?
Adding bromine water to an alkene causes the solution to decolourise from orange to colourless. The bromine atoms add across the C=C double bond, removing free bromine from solution.
True or False?
Bromine water remains orange when added to an alkene.
False.
Alkenes are unsaturated and contain a C=C double bond, which bromine reacts with. This causes the orange colour to decolourise / go colourless.
Define dibromoalkane.
A dibromoalkane is a saturated organic compound formed when bromine adds across the C=C double bond of an alkene, with one bromine atom bonding to each of the two carbon atoms.
In the bromine water test, an alkane gives an .......... colour, while an alkene causes the solution to .......... .
In the bromine water test, an alkane gives an orange colour, while an alkene causes the solution to decolourise.
Why is bromine water used instead of bromine gas to test for alkenes?
Bromine water is used instead of bromine gas because it is safer and easier to handle. It still decolourises in the presence of an alkene, giving a clear positive result.
True or False?
The bromine water test can distinguish between an alkane and an alkene.
True.
Bromine water remains orange with an alkane but decolourises with an alkene, making it a reliable test to distinguish between the two types of hydrocarbon.
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