30 Short Questions & Answers

Each answer is concise but explanatory — suitable for 2–4 mark questions and classroom assessments.

1. 1. What is catenation and why is it important for carbon? Catenation is carbon's ability to form strong C–C bonds and make long chains and rings; it underlies the vast diversity of organic compounds and is crucial to organic chemistry.
2. 2. Explain tetravalency of carbon with an example. Tetravalency means carbon has four valence electrons and forms four covalent bonds; for example, in methane (CH₄) carbon forms four single bonds with hydrogen atoms.
3. 3. Define homologous series and give an example. A homologous series is a group of compounds with the same functional group and successive members differing by CH₂; for example, the alkane series: methane, ethane, propane, etc.
4. 4. What is structural isomerism? Illustrate with C₄H₁₀. Structural isomerism occurs when molecules have the same formula but different connectivity; C₄H₁₀ gives n‑butane (straight chain) and isobutane (branched), which are structural isomers.
5. 5. How does hydrogen bonding influence the properties of alcohols? Hydrogen bonding between —OH groups of alcohols and water increases boiling points and solubility (for short chains), making alcohols have higher boiling points than comparable hydrocarbons.
6. 6. Describe the functional group and a key property of carboxylic acids. Carboxylic acids contain the —COOH group; they show acidic behaviour (donate H⁺ in solution) and often have higher boiling points due to hydrogen bonding.
7. 7. Write the chemical equation for esterification between ethanol and ethanoic acid. CH₃CH₂OH + CH₃COOH ⇌ CH₃COOCH₂CH₃ + H₂O (conc. H₂SO₄ as catalyst). The reaction is reversible and needs acid catalyst and heating.
8. 8. What is saponification? Provide a simple equation. Saponification is the alkaline hydrolysis of fats/oils to produce glycerol and soap; for example, triglyceride + 3NaOH → glycerol + 3 sodium fatty acid salts (soap).
9. 9. Why do soaps not work well in hard water? Soaps react with Ca²⁺ and Mg²⁺ in hard water to form insoluble scum (calcium or magnesium salts), reducing cleaning efficiency; detergents are designed to work in hard water.
10. 10. Explain why ethanol is soluble in water whereas hexane is not. Ethanol has a polar —OH group that forms hydrogen bonds with water, making it miscible; hexane is non‑polar and cannot hydrogen bond, so it is insoluble in water.
11. 11. State and explain the general formula for alkanes. Alkanes follow CₙH₂ₙ₊₂ because each carbon forms four single bonds (saturated hydrocarbons), e.g., C₁H₄, C₂H₆, C₃H₈, etc.
12. 12. What products are formed on complete combustion of a hydrocarbon? Complete combustion of hydrocarbons in excess oxygen yields carbon dioxide (CO₂) and water (H₂O), releasing energy; incomplete combustion may produce carbon monoxide (CO) or soot.
13. 13. How does branching affect the boiling point of hydrocarbons? Branching reduces surface area, lowering van der Waals forces between molecules, which generally decreases boiling points compared to straight-chain isomers.
14. 14. Describe oxidation of a primary alcohol — what are possible products? Primary alcohols can be oxidised first to aldehydes (R–CHO) and further to carboxylic acids (R–COOH) under strong oxidising conditions; controlled oxidation yields aldehydes.
15. 15. Give two everyday uses of esters. Esters are used as flavouring agents and in perfumes due to their pleasant fruity odours; they also appear in solvents and plasticizers.
16. 16. What is meant by 'functional group' in organic chemistry? A functional group is a specific group of atoms within a molecule that confers characteristic chemical reactions to that molecule, e.g., —OH, —COOH, —NH₂.
17. 17. Explain why carboxylic acids are often soluble in water (short chains). Short-chain carboxylic acids form hydrogen bonds with water due to the polar —COOH group, enhancing solubility; solubility decreases with longer hydrocarbon chains.
18. 18. What chemical test distinguishes between alcohols and carboxylic acids? Carboxylic acids react with carbonates (e.g., Na₂CO₃) to produce CO₂ gas (effervescence), whereas alcohols do not show this reaction under normal conditions.
19. 19. Name the reagent commonly used to oxidise alcohols in the lab. Potassium permanganate (KMnO₄) or acidified potassium dichromate (K₂Cr₂O₇/H₂SO₄) are used as oxidising agents to oxidise alcohols.
20. 20. How are soaps manufactured from natural fats? Soaps are made by saponification: natural fats (triglycerides) are treated with NaOH, splitting into glycerol and sodium salts of fatty acids (soap).
21. 21. What is the structural difference between an aldehyde and a ketone? An aldehyde has a carbonyl group (C=O) at the end of a carbon chain (—CHO), while a ketone has the carbonyl group within the chain (R–CO–R').
22. 22. Why are esters often volatile and fragrant? Esters typically have relatively low boiling points and are volatile; their specific molecular structures interact to produce distinctive pleasant odours used in fragrances and flavourings.
23. 23. Provide a short answer: how does ethanol react with sodium metal? Ethanol reacts with sodium to produce sodium ethoxide and hydrogen gas: 2CH₃CH₂OH + 2Na → 2CH₃CH₂ONa + H₂↑.
24. 24. What happens when ethanoic acid reacts with ethanol in presence of conc. H₂SO₄? They undergo esterification to form ethyl ethanoate (an ester) and water; concentrated sulfuric acid acts as a dehydrating catalyst.
25. 25. How can you distinguish ethanol from ethanoic acid by smell and taste (in a lab-safe observation)? Ethanol smells sweetish and is less pungent, while ethanoic acid has a sharp, vinegar‑like odour; tasting chemicals is unsafe—use small smelling techniques and caution.
26. 26. Explain why longer-chain hydrocarbons are less volatile than shorter ones. Longer-chain hydrocarbons have greater surface area and stronger van der Waals forces, requiring more energy to separate molecules, hence lower volatility and higher boiling points.
27. 27. What is meant by 'saturated' and 'unsaturated' hydrocarbons? Saturated hydrocarbons (alkanes) contain only single C–C bonds; unsaturated hydrocarbons (alkenes, alkynes) have double or triple bonds and can undergo addition reactions.
28. 28. Give a brief explanation of why detergents are preferred over soaps in certain situations. Detergents contain sulphonate groups that do not form insoluble scum with hard water ions (Ca²⁺/Mg²⁺), so they clean effectively in hard water and industrial applications.
29. 29. What is the importance of IUPAC nomenclature in organic chemistry? IUPAC nomenclature provides a standardized, unambiguous way to name organic compounds so chemists worldwide can identify structures and avoid confusion.
30. 30. Summarise in two lines why carbon forms the basis of organic chemistry. Carbon's tetravalency, small atomic size, and strong C–C bond (catenation) allow it to form diverse and stable chains and rings, producing vast numbers of organic compounds essential to life and materials.

Study tip: Turn each short answer into a one‑sentence explanation in your own words and practise by writing balanced equations wherever applicable.