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SingaporeCombined ScienceQuick questions

Chemistry: Metals and Organic Chemistry

Quick questions on Alkanes, alkenes and homologous series explained: O-Level Combined Science

7short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.

What are alkanes?
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Alkanes have the general formula CnH2n+2\text{C}_n\text{H}_{2n+2} and contain only single carbon-carbon bonds, so they are saturated. Examples are methane CH4\text{CH}_4, ethane C2H6\text{C}_2\text{H}_6 and propane C3H8\text{C}_3\text{H}_8. Their main reactions are:
What are alkenes?
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Alkenes have the general formula CnH2n\text{C}_n\text{H}_{2n} and contain a carbon-carbon double bond (C=C\text{C=C}), so they are unsaturated. Examples are ethene C2H4\text{C}_2\text{H}_4 and propene C3H6\text{C}_3\text{H}_6. Because of the reactive double bond, their main reactions are addition reactions:
What is the bromine-water test?
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Bromine water (orange/brown) is the standard test:
What are unbalanced combustion equations?
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Check that carbon, hydrogen and oxygen all balance, often needing a fraction or doubling.
What is q1?
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State the general formula of the alkanes and the general formula of the alkenes. [2 marks]
What is q2?
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Describe how you would use bromine water to distinguish ethane from ethene, with the observations. [2 marks]
What is q3?
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Name the type of reaction when ethene reacts with bromine, and write the equation. [2 marks]

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