Carbon compounds
Short Questions
1. What are organic compounds?
Answer : Organic compounds are carbon-containing compounds, excluding CO₂, CO, carbides, carbonates, and bicarbonates.
2. Why are carbon compounds called covalent compounds?
Answer : Carbon compounds form covalent bonds by sharing electrons, not ionic bonds.
3. What is a covalent bond?
Answer : A covalent bond is formed by sharing valence electrons between two atoms.
4. What is catenation?
Answer : Catenation is carbon’s ability to form strong covalent bonds with other carbon atoms, creating large molecules.
5. What are hydrocarbons?
Answer : Hydrocarbons are organic compounds containing only carbon and hydrogen atoms.
6. What are saturated hydrocarbons?
Answer : Saturated hydrocarbons (alkanes) have only single bonds between carbon atoms.
7. What are unsaturated hydrocarbons?
Answer : Unsaturated hydrocarbons (alkenes and alkynes) have double or triple bonds between carbon atoms.
8. What is structural isomerism?
Answer : Structural isomerism is when compounds with the same molecular formula have different structural arrangements.
9. What is a functional group?
Answer : A functional group is a group of atoms that determines the chemical properties of a carbon compound.
10. What is a homologous series?
Answer : A homologous series is a group of compounds with the same functional group and increasing carbon chain length.
11. What is the general formula for alkanes?
Answer : The general formula for alkanes is CₙH₂ₙ₊₂.
12. What is the general formula for alkenes?
Answer : The general formula for alkenes is CₙH₂ₙ.
13. What is the IUPAC nomenclature system?
Answer : IUPAC nomenclature is a standardized system for naming carbon compounds based on their structure.
14. What is combustion in carbon compounds?
Answer : Combustion is the reaction of carbon compounds with oxygen, producing CO₂, H₂O, heat, and light.
15. What is an addition reaction?
Answer : An addition reaction occurs when an unsaturated compound adds atoms to form a saturated compound.
16. What is a substitution reaction?
Answer : A substitution reaction replaces one atom or group in a molecule with another, typically in alkanes.
17. What is ethanol commonly known as?
Answer : Ethanol is commonly known as alcohol or spirit.
18. What is glacial acetic acid?
Answer : Glacial acetic acid is pure ethanoic acid, which freezes at 17°C, resembling ice.
19. What is a polymer?
Answer : A polymer is a macromolecule formed by the repetition of small units called monomers.
20. What is saponification?
Answer : Saponification is the reaction of an ester with a base to form soap and alcohol.
Long Questions
1. Explain why carbon forms a large number of compounds.
Answer : Carbon’s tetravalency allows it to form four covalent bonds with various atoms, including itself. Its catenation ability enables the formation of long chains and rings, increasing compound diversity. Isomerism further multiplies the number of compounds with the same molecular formula.
2. Describe the covalent bond formation in carbon compounds with an example.
Answer : Carbon shares its four valence electrons to form covalent bonds, achieving a stable noble gas configuration. For example, in methane (CH₄), carbon shares one electron with each of four hydrogen atoms, forming four single covalent bonds. This sharing ensures no ions are formed, keeping the molecule neutral.
3. What is the difference between saturated and unsaturated hydrocarbons?
Answer : Saturated hydrocarbons (alkanes) have only single C-C bonds, making them less reactive, e.g., ethane (C₂H₆). Unsaturated hydrocarbons (alkenes and alkynes) contain double or triple bonds, increasing reactivity, e.g., ethene (C₂H₄). Unsaturated compounds undergo addition reactions, unlike saturated ones.
4. Explain the concept of structural isomerism with an example.
Answer : Structural isomerism occurs when compounds with the same molecular formula have different structural arrangements. For example, butane (C₄H₁₀) has two isomers: n-butane (straight chain) and isobutane (branched chain). These isomers differ in properties due to their distinct structures.
5. Describe the characteristics of a homologous series.
Answer : A homologous series has compounds with the same functional group and general formula, differing by a -CH₂- unit. Each member’s molecular mass increases by 14 u, and physical properties show gradation, e.g., boiling points rise in alkanes. Chemical properties remain similar due to the same functional group.
6. How is the IUPAC name of a carbon compound determined?
Answer : The IUPAC name consists of a prefix, parent, and suffix based on the compound’s structure. The parent is the longest carbon chain, with suffixes like -ene or -yne for double or triple bonds. Numbering ensures the functional group gets the lowest possible number, e.g., propan-2-ol.
7. Explain the combustion reaction of carbon compounds with examples.
Answer : Carbon compounds burn in oxygen to produce CO₂, H₂O, heat, and light, e.g., CH₄ + 2O₂ → CO₂ + 2H₂O. Saturated compounds like ethanol burn with a clean blue flame, while unsaturated ones like naphthalene produce sooty yellow flames. Combustion is exothermic, releasing energy.
8. Describe the oxidation reaction of ethanol and its significance.
Answer : Ethanol (CH₃CH₂OH) is oxidized by alkaline potassium permanganate to form ethanoic acid (CH₃COOH). The pink color of KMnO₄ disappears as it’s consumed, indicating oxidation completion. This reaction demonstrates the transformation of an alcohol’s functional group into a carboxylic acid.
9. What is an addition reaction, and how is it used to test unsaturation?
Answer : An addition reaction involves an unsaturated compound adding atoms across its multiple bond, forming a saturated product. For example, ethene reacts with bromine, decolorizing orange bromine water, confirming a double bond. This test distinguishes unsaturated oils from saturated Vanaspati ghee.
10. Explain the substitution reaction in alkanes with an example.
Answer : Substitution reactions replace hydrogen atoms in alkanes with other atoms, like chlorine, in sunlight. For example, methane (CH₄) reacts with Cl₂ to form chloromethane (CH₃Cl) and HCl: CH₄ + Cl₂ → CH₃Cl + HCl. Multiple substitutions can occur, producing compounds like CCl₄.
11. Describe the chemical properties of ethanol and their applications.
Answer : Ethanol reacts with sodium to form sodium ethoxide and hydrogen, indicating its acidic -OH group. It undergoes dehydration with concentrated H₂SO₄ at 170°C to form ethene, used in polymer synthesis. As a solvent, ethanol is used in medicines and tinctures due to its reactivity.
12. Explain the chemical properties of ethanoic acid and its uses.
Answer : Ethanoic acid reacts with bases like NaOH to form sodium ethanoate and water, and with carbonates to produce CO₂, e.g., 2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂. It forms esters with alcohols, used in fragrances. Its 5-8% solution (vinegar) is a preservative.
13. What is esterification, and how is it reversed?
Answer : Esterification is the reaction of a carboxylic acid with an alcohol, forming an ester and water, e.g., CH₃COOH + C₂H₅OH → CH₃COOC₂H₅ + H₂O. Concentrated H₂SO₄ catalyzes this reaction. Saponification reverses it, using NaOH to regenerate the alcohol and sodium carboxylate.
14. What are polymers, and how are they formed?
Answer : Polymers are macromolecules formed by repeating monomer units through polymerization, e.g., polyethylene from ethylene. Natural polymers like starch consist of glucose monomers, while synthetic ones like nylon use multiple monomers. Catalysts and specific conditions facilitate the bonding of monomers into long chains.
15. Describe the significance of natural and man-made macromolecules.
Answer : Natural macromolecules like proteins, polysaccharides, and nucleic acids support life, forming body structures and controlling heredity. Man-made macromolecules, such as plastics and synthetic fibers, provide durable materials like polyethylene and nylon for various applications. Their polymeric nature allows tailored properties for specific uses, e.g., elastomers in tires.
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