The table gives information about four homologous series of organic compounds. Homologous series Functional group General formula Name of first member alkan...
Question 1 Report
The table gives information about four homologous series of organic compounds.
| Homologous series | Functional group | General formula | Name of first member |
|---|---|---|---|
| alkanes | none (C-C single bonds) | CnH2n+2 | methane |
| alkenes | C=C double bond | ........... | ethene |
| alcohols | ........... | CnH2n+1OH | methanol |
| carboxylic acids | -COOH | CnH2n+1COOH | ........... |
(a) Complete the three gaps in the table: the general formula of the alkenes, the functional group of the alcohols and the name of the first member of the carboxylic acids. [3]
(b) State the name given to the -COOH functional group of the carboxylic acids. [1]
(c) Name the functional group that is present in every alkene. [1]
(d) Give the general formula of the carboxylic acids. [1]
(e) Name the second member of the carboxylic acid series. [1]
(f) State the difference between an alkane molecule and an alkene molecule in terms of the bonding between the carbon atoms. [2]
(g) Deduce the molecular formula of the alkene that contains five carbon atoms. [1]
(h) Explain why all the members of a single homologous series have similar chemical properties. [2]
Answer Details
This question is built around the idea of a homologous series: a family of compounds with the same functional group, the same general formula, and a gradual change in physical properties. Fill the gaps and then explain that idea.
(a) The three missing entries are:
- general formula of the alkenes: CnH2n [1]
- functional group of the alcohols: the hydroxyl (-OH) group [1]
- first carboxylic acid: methanoic acid [1]
(b) The -COOH group is called the carboxyl group [1].
(c) Every alkene contains a carbon-carbon double bond, C=C [1].
(d) The general formula of the carboxylic acids is CnH2n+1COOH (the form CnH2nO2 is also accepted) [1].
(e) After methanoic acid, the second member is ethanoic acid [1].
(f) In an alkane the carbon atoms are joined only by single (C-C) bonds, so it is saturated [1]; in an alkene at least one pair of carbons is joined by a double (C=C) bond, so it is unsaturated [1].
(g) For five carbons in the alkenes, \( \text{H} = 2n = 2(5) = 10 \), so the formula is C5H10 [1].
(h) All members of one homologous series have the same functional group [1], and it is the functional group that determines the chemical reactions, so they react in the same way [1].
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