iGCSE Chemistry (0620) Core:11.1 Formulae, functional groups and terminology: Exam Style Questions Paper 1- New Syllabus
▶️ Answer/Explanation
Detailed solution:
Alkanes are saturated hydrocarbons with only single bonds, so statement 3 is false. Because they have no double bonds, they do not decolourise bromine water (statement 4 false). They have the general formula $\text{C}_n\text{H}_{2n+2}$ (statement 2 true) and are generally unreactive except for combustion and substitution reactions (statement 1 true). So, 1 and 2 are correct.
▶️ Answer/Explanation
Detailed solution:
The general formula for a carboxylic acid is $\text{C}_n\text{H}_{2n+1}\text{COOH}$, which works out to $\text{C}_n\text{H}_{2n}\text{O}_2$. Y has the formula $\text{C}_4\text{H}_8\text{O}_2$, which fits this pattern (with $n=4$). W has oxygen but doesn’t fit the alcohol general formula $\text{C}_n\text{H}_{2n+1}\text{OH}$; it’s not an alcohol. W contains oxygen, so it’s not a hydrocarbon. X could be propene, not ethene (ethene is $\text{C}_2\text{H}_4$). So only Y can be a carboxylic acid.
▶️ Answer/Explanation
Detailed solution:
Members of the same homologous series share the same general formula. Compounds 1 and 2 have formulas $C_2H_4$ and $C_4H_8$, which both fit the general formula for alkenes, $C_nH_{2n}$. They both contain a carbon-carbon double bond and belong to the alkene series. Compound 3 is $C_4H_{10}$, which fits the alkane general formula $C_nH_{2n+2}$ and has only single bonds. Since it belongs to a different homologous series from the other two, only 1 and 2 are in the same series.