A Level Chemistry OCR Practice Exam

Which statement correctly describes an alkane?

1. It is a cyclic compound

2. It contains double bonds

3. It is saturated with single bonds between carbon atoms

4. It has a branched structure only

The correct answer is: It is saturated with single bonds between carbon atoms

An alkane is correctly described as being saturated with single bonds between carbon atoms. This means that each carbon atom in an alkane is bonded to four other atoms (either carbon or hydrogen) through single covalent bonds, resulting in a fully "saturated" molecule that does not contain any double or triple bonds. Alkanes follow the general formula CₙH₂ₙ₊₂, which reflects their saturated nature. This characteristic is crucial because it distinguishes alkanes from other categories of hydrocarbons, such as alkenes and alkynes, which contain double and triple bonds, respectively. In contrast, while cyclic compounds exist within the hydrocarbons, not all alkanes are cyclic, as there are also linear and branched forms, making the first statement incomplete. The statement regarding double bonds is also incorrect, as this is characteristic of alkenes. Lastly, alkanes can have both linear and branched structures; thus, implying that they have a branched structure only is misleading. Hence, the definition of an alkane as a saturated compound with single bonds is what makes the chosen answer accurate.