CBSE Class 10 Science Chemistry
Carbon and Its Compounds Important Questions and Answers for Class 10 CBSE
NCERT + Board Exam + Exemplar + Olympiad level question bank covering covalent bonding, hydrocarbons, homologous series, functional groups, ethanol, ethanoic acid, soaps, detergents and cleansing action.
Short Introduction
The chapter Carbon and Its Compounds explains why carbon forms a huge number of compounds. It covers covalent bonding, tetravalency, catenation, hydrocarbons, homologous series, functional groups, important carbon compounds like ethanol and ethanoic acid, and cleansing agents such as soaps and detergents. This chapter is very important for CBSE board exams because it includes definitions, structural formulae, chemical reactions, reasoning questions and application-based questions.
Chapter Overview
Covalent Bonding
Carbon forms covalent bonds by sharing electrons because it has four valence electrons.
Tetravalency
Carbon has valency four, so it can form four covalent bonds with other atoms.
Catenation
Carbon can form long chains, branched chains and rings by bonding with other carbon atoms.
Hydrocarbons
Compounds of carbon and hydrogen are called hydrocarbons. They may be saturated or unsaturated.
Functional Groups
Functional groups decide the chemical properties of carbon compounds.
Soaps and Detergents
Soaps and detergents clean oily dirt by forming micelles.
Important Keywords
Important Very Short Answer Questions
Q1. What is a covalent bond?
Answer: A covalent bond is formed by sharing of electrons between two atoms.
Q2. Why does carbon form covalent bonds?
Answer: Carbon has four valence electrons. It can neither lose four electrons nor gain four electrons easily, so it shares electrons and forms covalent bonds.
Q3. What is tetravalency of carbon?
Answer: The ability of carbon to form four covalent bonds is called tetravalency.
Q4. What is catenation?
Answer: The property of carbon to form bonds with other carbon atoms and make long chains, branched chains and rings is called catenation.
Q5. Why are carbon compounds stable?
Answer: Carbon compounds are stable because carbon forms strong covalent bonds due to its small atomic size.
Q6. What are hydrocarbons?
Answer: Compounds made up of only carbon and hydrogen are called hydrocarbons.
Q7. What are saturated hydrocarbons?
Answer: Hydrocarbons containing only single bonds between carbon atoms are called saturated hydrocarbons. Example: ethane.
Q8. What are unsaturated hydrocarbons?
Answer: Hydrocarbons containing double or triple bonds between carbon atoms are called unsaturated hydrocarbons. Example: ethene, ethyne.
Q9. What is the general formula of alkanes?
Answer: CnH2n+2.
Q10. What is the general formula of alkenes?
Answer: CnH2n.
Q11. What is the general formula of alkynes?
Answer: CnH2n−2.
Q12. What is a homologous series?
Answer: A series of organic compounds having the same functional group and similar chemical properties, where two successive members differ by CH2, is called a homologous series.
Q13. What is a functional group?
Answer: An atom or group of atoms that decides the chemical properties of an organic compound is called a functional group.
Q14. What is the functional group of alcohols?
Answer: Hydroxyl group, −OH.
Q15. What is the functional group of carboxylic acids?
Answer: Carboxyl group, −COOH.
Q16. What is the IUPAC name of acetic acid?
Answer: Ethanoic acid.
Q17. What is vinegar?
Answer: Vinegar is a 5–8% solution of ethanoic acid in water.
Q18. What is saponification?
Answer: The reaction of an ester with sodium hydroxide to form soap and alcohol is called saponification.
Q19. What is a micelle?
Answer: A micelle is a spherical structure formed by soap molecules in water, where hydrophobic tails are inside and hydrophilic heads are outside.
Q20. What is hydrogenation?
Answer: The addition of hydrogen to unsaturated hydrocarbons or oils in the presence of a catalyst like nickel is called hydrogenation.
Short Answer Questions
Q1. Why does carbon not form C4+ or C4− ions?
Answer:
- Carbon has four valence electrons.
- Losing four electrons requires a very large amount of energy.
- Gaining four electrons is difficult because the nucleus cannot hold ten electrons strongly.
- Therefore, carbon completes its octet by sharing electrons and forms covalent bonds.
Q2. Write four properties of covalent compounds.
Answer:
- They usually have low melting and boiling points.
- They are generally poor conductors of electricity.
- They are usually insoluble in water but soluble in organic solvents.
- They are formed by sharing of electrons.
Q3. Why is carbon able to form a large number of compounds?
Answer: Carbon forms a large number of compounds because of:
- Tetravalency: Carbon can form four covalent bonds.
- Catenation: Carbon can form long chains, branched chains and rings.
- Strong carbon-carbon bonds: Due to small atomic size, carbon forms stable bonds.
Q4. Differentiate between saturated and unsaturated hydrocarbons.
| Saturated Hydrocarbons | Unsaturated Hydrocarbons |
|---|---|
| They contain only single bonds. | They contain at least one double or triple bond. |
| They are less reactive. | They are more reactive. |
| Example: Ethane, C2H6 | Example: Ethene, C2H4; Ethyne, C2H2 |
Q5. What are alkanes, alkenes and alkynes?
Answer:
- Alkanes: Saturated hydrocarbons with single bonds. General formula: CnH2n+2.
- Alkenes: Unsaturated hydrocarbons with at least one double bond. General formula: CnH2n.
- Alkynes: Unsaturated hydrocarbons with at least one triple bond. General formula: CnH2n−2.
Q6. What is an alkyl group?
Answer: An alkyl group is formed by removing one hydrogen atom from an alkane. Its general formula is CnH2n+1. Example: CH3− is methyl and C2H5− is ethyl.
Q7. Write the first four members of the alkane series.
| Name | Formula | Structure |
|---|---|---|
| Methane | CH4 | CH4 |
| Ethane | C2H6 | CH3−CH3 |
| Propane | C3H8 | CH3−CH2−CH3 |
| Butane | C4H10 | CH3−CH2−CH2−CH3 |
Q8. What are functional groups? Give examples.
Answer: Functional groups are atoms or groups of atoms that decide the chemical properties of organic compounds.
| Functional Group | Class of Compound | Example |
|---|---|---|
| −Cl, −Br | Haloalkane | Chloromethane, CH3Cl |
| −OH | Alcohol | Ethanol, C2H5OH |
| −CHO | Aldehyde | Ethanal, CH3CHO |
| >C=O | Ketone | Propanone, CH3COCH3 |
| −COOH | Carboxylic acid | Ethanoic acid, CH3COOH |
Q9. What is substitution reaction? Give example.
Answer: A reaction in which one atom or group of atoms replaces another atom or group in a compound is called substitution reaction.
Example: Methane reacts with chlorine in sunlight to form chloromethane.
CH4 + Cl2 → CH3Cl + HCl
Q10. What is hydrogenation? Write its use.
Answer: Hydrogenation is the addition of hydrogen to unsaturated compounds in the presence of a catalyst such as nickel, palladium or platinum.
Vegetable oil + H2 → Vegetable ghee
Use: It is used to convert unsaturated vegetable oils into saturated fats like vanaspati ghee.
Q11. Differentiate between saturated and unsaturated oils.
Answer:
- Saturated oils/fats: Contain mainly single bonds and are generally solid at room temperature.
- Unsaturated oils: Contain double bonds and are generally liquid at room temperature.
- Unsaturated oils are considered healthier than saturated fats when consumed in suitable amounts.
Q12. Why are detergents called soapless soaps?
Answer: Detergents are called soapless soaps because they act like soaps in cleansing but are not sodium or potassium salts of fatty acids. They can work even in hard water.
Long Answer Questions
Q1. Explain why carbon forms only covalent compounds and why carbon compounds are stable.
Answer:
- Carbon has atomic number 6 and electronic configuration 2,4.
- It has four electrons in its outermost shell.
- Carbon cannot lose four electrons easily because it requires a very large amount of energy.
- Carbon cannot gain four electrons easily because the nucleus cannot hold ten electrons strongly.
- Therefore, carbon shares electrons and forms covalent bonds.
- Carbon compounds are stable because carbon has small atomic size and forms strong covalent bonds.
Q2. Explain catenation and tetravalency as the two special properties of carbon.
Answer:
- Catenation: Carbon can form strong bonds with other carbon atoms. Due to this, carbon forms long chains, branched chains and ring structures.
- Tetravalency: Carbon has valency four. It can form four covalent bonds with carbon, hydrogen, oxygen, nitrogen, sulphur, chlorine and many other elements.
- Because of catenation and tetravalency, carbon forms a very large number of compounds.
Q3. Explain homologous series with characteristics.
Answer: A homologous series is a series of organic compounds having the same functional group and similar chemical properties.
Characteristics:
- All members have the same functional group.
- All members have similar chemical properties.
- Two consecutive members differ by CH2.
- Difference in molecular mass between two consecutive members is 14 u.
- Physical properties such as boiling point and melting point change gradually.
Example: Alcohol series: CH3OH, C2H5OH, C3H7OH.
Q4. Explain the physical and chemical properties of ethanol.
Answer:
Physical properties of ethanol:
- Ethanol is a colourless liquid.
- It has a characteristic smell.
- It is soluble in water in all proportions.
- It has a lower boiling point than water.
Chemical properties of ethanol:
- Combustion: Ethanol burns with a clean blue flame.
C2H5OH + 3O2 → 2CO2 + 3H2O + heat
- Reaction with sodium: Ethanol reacts with sodium to form sodium ethoxide and hydrogen gas.
2C2H5OH + 2Na → 2C2H5ONa + H2
- Oxidation: Ethanol is oxidised to ethanoic acid using alkaline KMnO4 or acidified K2Cr2O7.
CH3CH2OH + 2[O] → CH3COOH + H2O
- Dehydration: Ethanol gives ethene when heated with concentrated H2SO4 at 443 K.
CH3CH2OH → CH2=CH2 + H2O
Q5. Explain the physical and chemical properties of ethanoic acid.
Answer:
Physical properties of ethanoic acid:
- Ethanoic acid is a colourless liquid with a pungent smell.
- It is soluble in water.
- Its 5–8% solution in water is called vinegar.
- Pure ethanoic acid freezes at about 290 K and is called glacial acetic acid.
Chemical properties of ethanoic acid:
- Reaction with base:
CH3COOH + NaOH → CH3COONa + H2O
- Reaction with carbonates:
2CH3COOH + Na2CO3 → 2CH3COONa + H2O + CO2
- Reaction with hydrogen carbonates:
CH3COOH + NaHCO3 → CH3COONa + H2O + CO2
- Esterification: Ethanoic acid reacts with ethanol in the presence of concentrated sulphuric acid to form an ester.
CH3COOH + C2H5OH → CH3COOC2H5 + H2O
Q6. Explain esterification and saponification reactions.
Answer:
Esterification: The reaction between a carboxylic acid and an alcohol in the presence of concentrated sulphuric acid to form an ester is called esterification.
CH3COOH + C2H5OH → CH3COOC2H5 + H2O
Saponification: The alkaline hydrolysis of an ester to form alcohol and sodium salt of carboxylic acid is called saponification.
CH3COOC2H5 + NaOH → CH3COONa + C2H5OH
Q7. Explain the structure of a soap molecule and cleaning action of soap.
Answer:
- A soap molecule has two parts: a long hydrocarbon tail and an ionic head.
- The hydrocarbon tail is hydrophobic, meaning it repels water and dissolves in oil or grease.
- The ionic head is hydrophilic, meaning it dissolves in water.
- In water, soap molecules arrange themselves around oily dirt and form micelles.
- The tails remain inside the oil droplet while the heads remain outside in water.
- On rinsing, the micelles are washed away with water, removing dirt and grease.
Q8. Why do soaps not work well in hard water? How are detergents better?
Answer:
- Hard water contains calcium and magnesium ions.
- Soap reacts with these ions to form an insoluble substance called scum.
- Due to scum formation, soap does not produce good lather and cleaning becomes difficult.
- Detergents do not form insoluble scum with calcium and magnesium ions.
- Therefore, detergents are effective even in hard water.
Important Tables for Quick Learning
Functional Groups in Carbon Compounds
| Class | Functional Group | General Representation | Example |
|---|---|---|---|
| Haloalkane | −Cl, −Br, −I | R−X | Chloromethane, CH3Cl |
| Alcohol | −OH | R−OH | Ethanol, C2H5OH |
| Aldehyde | −CHO | R−CHO | Ethanal, CH3CHO |
| Ketone | >C=O | R−CO−R | Propanone, CH3COCH3 |
| Carboxylic acid | −COOH | R−COOH | Ethanoic acid, CH3COOH |
Hydrocarbon Series
| Series | Bond Type | General Formula | Example |
|---|---|---|---|
| Alkane | Single bond | CnH2n+2 | Ethane, C2H6 |
| Alkene | Double bond | CnH2n | Ethene, C2H4 |
| Alkyne | Triple bond | CnH2n−2 | Ethyne, C2H2 |
Important Reactions of Ethanol and Ethanoic Acid
| Reaction | Equation | Important Point |
|---|---|---|
| Ethanol with sodium | 2C2H5OH + 2Na → 2C2H5ONa + H2 | Hydrogen gas is evolved. |
| Oxidation of ethanol | CH3CH2OH + 2[O] → CH3COOH + H2O | Ethanol changes into ethanoic acid. |
| Ethanoic acid with NaOH | CH3COOH + NaOH → CH3COONa + H2O | Neutralisation reaction. |
| Ethanoic acid with NaHCO3 | CH3COOH + NaHCO3 → CH3COONa + H2O + CO2 | CO2 gas is evolved. |
| Esterification | CH3COOH + C2H5OH → CH3COOC2H5 + H2O | Sweet-smelling ester is formed. |
Case-Study Based Questions
Case Study 1: Covalent Nature of Carbon
Carbon has four electrons in its outermost shell. It forms compounds with hydrogen, oxygen, chlorine and many other elements by sharing electrons.
Q1. What is the valency of carbon?
Answer: The valency of carbon is four.
Q2. Why does carbon form covalent bonds?
Answer: Carbon shares electrons because losing or gaining four electrons is energetically difficult.
Q3. Name the property by which carbon forms long chains.
Answer: Catenation.
Case Study 2: Ethanol and Ethanoic Acid
A student oxidises ethanol using alkaline potassium permanganate. The product formed has a sour taste and reacts with sodium hydrogen carbonate to produce carbon dioxide gas.
Q1. Identify the product formed by oxidation of ethanol.
Answer: Ethanoic acid.
Q2. Write the oxidation reaction.
CH3CH2OH + 2[O] → CH3COOH + H2O
Q3. What gas is evolved when ethanoic acid reacts with sodium hydrogen carbonate?
Answer: Carbon dioxide gas.
Case Study 3: Soap and Hard Water
Riya observes that soap does not produce good lather with hard water. Instead, a white insoluble substance is formed.
Q1. What is the white insoluble substance called?
Answer: Scum.
Q2. Why is scum formed?
Answer: Soap reacts with calcium and magnesium ions present in hard water to form insoluble scum.
Q3. Which cleansing agent works better in hard water?
Answer: Detergent.
Case Study 4: Hydrogenation of Oils
Vegetable oils are treated with hydrogen in the presence of nickel catalyst to form vanaspati ghee.
Q1. What is this reaction called?
Answer: Hydrogenation.
Q2. What type of oils undergo hydrogenation?
Answer: Unsaturated oils.
Q3. What is the role of nickel?
Answer: Nickel acts as a catalyst.
Critical Thinking Questions
Q1. Why does carbon form millions of compounds whereas silicon forms fewer compounds?
Answer: Carbon has a smaller atomic size and forms strong carbon-carbon bonds. Silicon has a larger atomic size and silicon-silicon bonds are weaker. Therefore, carbon shows better catenation and forms more compounds.
Q2. Why are covalent compounds generally poor conductors of electricity?
Answer: Covalent compounds are made of molecules and do not contain free ions or free electrons. Therefore, they generally do not conduct electricity.
Q3. Why do unsaturated hydrocarbons undergo addition reactions?
Answer: Unsaturated hydrocarbons contain double or triple bonds. These bonds can break partially and allow addition of atoms such as hydrogen, chlorine or bromine.
Q4. Why do alkanes mainly undergo substitution reactions?
Answer: Alkanes are saturated hydrocarbons with strong single covalent bonds. They do not easily undergo addition reactions, so they mainly undergo substitution reactions.
Q5. Why is ethanol soluble in water?
Answer: Ethanol contains the polar −OH group, which forms hydrogen bonding with water. Therefore, ethanol is soluble in water.
Q6. Why is ethanoic acid called glacial acetic acid in pure form?
Answer: Pure ethanoic acid freezes at about 290 K and forms ice-like crystals. Therefore, it is called glacial acetic acid.
Q7. Why is alkaline KMnO4 called an oxidising agent?
Answer: Alkaline KMnO4 adds oxygen to ethanol and converts it into ethanoic acid. Therefore, it acts as an oxidising agent.
Q8. Why are detergents more effective than soaps in hard water?
Answer: Detergents do not form insoluble precipitates with calcium and magnesium ions present in hard water. Therefore, they clean effectively in hard water.
Q9. Why does soap form micelles only above a certain concentration?
Answer: Soap molecules form micelles only when enough soap molecules are present to arrange their hydrophobic tails inside and hydrophilic heads outside in water.
Q10. Why is hydrogenation used in the food industry?
Answer: Hydrogenation converts liquid vegetable oils into semi-solid fats like vanaspati ghee, which have better texture and longer shelf life.
Previous Year Board Exam Pattern Questions
Q1. What would be the electron dot structure of methane?
Answer: Methane, CH4, has one carbon atom sharing one electron each with four hydrogen atoms. Carbon completes its octet and each hydrogen completes its duplet.
Q2. Give reasons: Carbon forms covalent compounds.
Answer: Carbon has four valence electrons. Losing or gaining four electrons is difficult. Therefore, carbon completes its octet by sharing electrons and forms covalent compounds.
Q3. Why are carbon and its compounds used as fuels?
Answer: Carbon compounds release a large amount of heat and light on combustion. Therefore, they are used as fuels.
CH4 + 2O2 → CO2 + 2H2O + heat
Q4. How can ethanol be converted into ethanoic acid?
Answer: Ethanol can be oxidised to ethanoic acid using alkaline potassium permanganate or acidified potassium dichromate.
CH3CH2OH + 2[O] → CH3COOH + H2O
Q5. Write the reaction of ethanoic acid with sodium carbonate.
Answer:
2CH3COOH + Na2CO3 → 2CH3COONa + H2O + CO2
Q6. Explain the cleansing action of soap.
Answer: Soap molecules form micelles around oily dirt. Their hydrophobic tails dissolve in grease, while hydrophilic heads remain in water. On rinsing, the micelles carrying dirt are washed away.
Q7. Why is soap not suitable for washing clothes with hard water?
Answer: Soap reacts with calcium and magnesium ions in hard water to form insoluble scum. This reduces lather formation and cleaning ability.
Q8. What happens when ethanol is heated with concentrated sulphuric acid at 443 K?
Answer: Ethanol undergoes dehydration and forms ethene.
CH3CH2OH → CH2=CH2 + H2O
Olympiad Level Questions
Q1. A hydrocarbon has formula C4H10. Identify its series.
Answer: C4H10 follows the alkane formula CnH2n+2. Therefore, it belongs to the alkane series.
Q2. A compound has the formula C3H6. Is it saturated or unsaturated?
Answer: C3H6 follows the alkene formula CnH2n. Therefore, it is an unsaturated hydrocarbon.
Q3. Two consecutive members of a homologous series have molecular masses 30 u and 44 u. What is the difference and why?
Answer: The difference is 14 u because consecutive members of a homologous series differ by one CH2 group.
Q4. A compound gives brisk effervescence with sodium hydrogen carbonate. Which functional group is likely present?
Answer: The compound likely contains the carboxylic acid group, −COOH, because carboxylic acids react with NaHCO3 to release CO2.
Q5. Why does bromine water become colourless when added to ethene?
Answer: Ethene is unsaturated and undergoes addition reaction with bromine. Therefore, bromine water loses its colour.
Q6. A sweet-smelling compound is formed when ethanol reacts with ethanoic acid. Identify the compound and reaction.
Answer: The compound is an ester, ethyl ethanoate. The reaction is esterification.
Q7. Why does methane undergo chlorination only in the presence of sunlight?
Answer: Sunlight provides energy to start the substitution reaction between methane and chlorine.
Q8. Why does soap solution appear cloudy in hard water?
Answer: Soap reacts with calcium and magnesium ions of hard water to form insoluble scum, making the solution cloudy.
Assertion-Reason Questions
Choose the correct option:
A. Both Assertion and Reason are true and Reason is the correct explanation.
B. Both Assertion and Reason are true but Reason is not the correct explanation.
C. Assertion is true but Reason is false.
D. Assertion is false but Reason is true.
Q1. Assertion: Carbon forms covalent compounds. Reason: Carbon completes its octet by sharing electrons.
Answer: A. Both Assertion and Reason are true and Reason is the correct explanation.
Q2. Assertion: Carbon compounds are stable. Reason: Carbon forms strong covalent bonds due to its small atomic size.
Answer: A. Both Assertion and Reason are true and Reason is the correct explanation.
Q3. Assertion: Alkanes undergo addition reactions easily. Reason: Alkanes contain only single covalent bonds.
Answer: D. Assertion is false but Reason is true. Alkanes generally undergo substitution reactions, not addition reactions.
Q4. Assertion: Ethanoic acid reacts with sodium hydrogen carbonate to produce carbon dioxide. Reason: Ethanoic acid is acidic in nature.
Answer: A. Both Assertion and Reason are true and Reason is the correct explanation.
Q5. Assertion: Detergents are effective in hard water. Reason: Detergents do not form insoluble scum with calcium and magnesium ions.
Answer: A. Both Assertion and Reason are true and Reason is the correct explanation.
Q6. Assertion: Soap molecules form micelles in water. Reason: Soap molecules have hydrophilic heads and hydrophobic tails.
Answer: A. Both Assertion and Reason are true and Reason is the correct explanation.
Quick Revision Box
Valency of Carbon
4
Bond Type
Covalent
Alkane Formula
CnH2n+2
Alkene Formula
CnH2n
Alkyne Formula
CnH2n−2
Alcohol Group
−OH
Carboxylic Acid
−COOH
Vinegar
5–8% ethanoic acid
Soap Action
Micelle formation
Exam Tips
Interactive Practice Zone
Hydrocarbon Formula Generator
Select the type of hydrocarbon and number of carbon atoms to generate the general formula.
Mini Quiz
Which functional group is present in ethanoic acid?
FAQ Section
Why does carbon form covalent bonds?
Carbon has four valence electrons. Losing or gaining four electrons is difficult, so carbon completes its octet by sharing electrons.
What are the two main reasons for the large number of carbon compounds?
The two main reasons are tetravalency and catenation.
What is the difference between alkanes, alkenes and alkynes?
Alkanes have single bonds, alkenes have double bonds and alkynes have triple bonds between carbon atoms.
What is a homologous series?
A homologous series is a series of organic compounds having the same functional group and similar chemical properties, where consecutive members differ by CH2.
What is vinegar?
Vinegar is a 5–8% solution of ethanoic acid in water.
What is esterification?
Esterification is the reaction between an alcohol and a carboxylic acid in the presence of concentrated sulphuric acid to form an ester.
Why do soaps not work well in hard water?
Soaps react with calcium and magnesium ions in hard water to form insoluble scum, which reduces cleansing action.
Why are detergents useful in hard water?
Detergents do not form insoluble scum with calcium and magnesium ions, so they clean effectively in hard water.
Final Conclusion
Carbon and Its Compounds is one of the most important Chemistry chapters in Class 10 Science. Students should focus on covalent bonding, tetravalency, catenation, hydrocarbons, homologous series, functional groups, ethanol, ethanoic acid, esterification, saponification and cleansing action of soaps. Regular practice of equations, structural formulae, reasoning questions and case-study questions will help students score high marks in CBSE board exams and competitive-level tests.
Leave a Reply