A Level Chemistry OCR Practice Exam

What defines an aliphatic hydrocarbon?

1. A hydrocarbon consisting solely of ring structures

2. A hydrocarbon with straight or branched carbon chains

3. A type of hydrocarbon containing both straight and ring structures

4. A hydrocarbon with only saturated bonds

The correct answer is: A hydrocarbon with straight or branched carbon chains

Aliphatic hydrocarbons are defined by having straight or branched carbon chains, which can be either saturated (with single bonds only) or unsaturated (containing double or triple bonds). This characteristic distinguishes them from other types of hydrocarbons, such as aromatic hydrocarbons, which contain certain stable ring structures. The correct answer aligns with this definition because aliphatic hydrocarbons encompass a wide variety of structures, including linear and branched forms. The other options involve misunderstandings of the definitions. For instance, hydrocarbons that consist solely of ring structures are classified as cyclic hydrocarbons, while those that contain both straight chains and rings would be considered complex or alicyclic hydrocarbons. The option referring to only saturated bonds describes saturated hydrocarbons, a subset of aliphatic hydrocarbons, but does not encompass the full category that includes unsaturated forms as well.