Organic ChemistryHow It Works
How the -OH Group Determines Properties
Part of Alcohols — GCSE Chemistry
This how it works covers How the -OH Group Determines Properties within Alcohols for GCSE Chemistry. Revise Alcohols in Organic Chemistry for GCSE Chemistry with 20 exam-style questions and 15 flashcards. This topic appears less often, but it can still be a useful differentiator on mixed-topic papers. It is section 3 of 13 in this topic. Use this how it works to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 3 of 13
Practice
20 questions
Recall
15 flashcards
⚙️ How the -OH Group Determines Properties
The -OH (hydroxyl) functional group is responsible for the distinctive properties of alcohols that set them apart from alkanes.
- Solubility in water: The -OH group can form hydrogen bonds with water molecules. Short-chain alcohols (methanol, ethanol) are completely miscible with water because the -OH group's ability to hydrogen bond outweighs the non-polar hydrocarbon chain. As chain length increases, solubility decreases because the hydrocarbon chain dominates.
- Higher boiling point than alkanes: Alcohol molecules can form hydrogen bonds with each other through their -OH groups. These bonds require extra energy to break, giving alcohols much higher boiling points than alkanes of similar size. Ethanol boils at 78°C; ethane boils at -89°C.
- Acidity: The O-H bond in alcohols can break to release H⁺ ions, but this happens only very slightly — alcohols are extremely weak acids, much weaker than carboxylic acids. They do not change litmus paper.
- Reactivity: The -OH group is a reactive functional group — it can be oxidised to a carboxylic acid, or replaced in substitution reactions.