Which equation correctly represents the reaction between ethanol and sodium?

2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂

C₂H₅OH + Na → C₂H₅Na + H₂O

2C₂H₅OH + Na → C₂H₅OC₂H₅ + H₂

C₂H₅OH + 2Na → C₂H₄ + NaOH + H₂

Soap molecules form micelles in water because they possess:

Both hydrophilic and hydrophobic parts

Assertion (A): Saturated hydrocarbons are less reactive than unsaturated hydrocarbons. Reason (R): Saturated hydrocarbons contain only single bonds, while unsaturated hydrocarbons contain double or triple bonds.

Both A and R are true and R is the correct explanation of A.

Both A and R are true but R is not the correct explanation of A.

A compound with molecular formula C₄H₈ decolorizes bromine water. Draw all possible straight‑chain structural isomers of this compound. Write the addition reaction with hydrogen for any one of the isomers.

Straight‑chain isomers: but‑1‑ene (CH₂=CH‒CH₂‒CH₃) and but‑2‑ene (CH₃‒CH=CH‒CH₃). Addition reaction (for but‑1‑ene): CH₂=CH‒CH₂‒CH₃ + H₂ → CH₃‒CH₂‒CH₂‒CH₃ (in presence of Ni catalyst). The product is butane.

n‑Butane and iso‑butane have the same molecular mass but different boiling points. Which one has the higher boiling point? Explain your answer by relating the structure to intermolecular forces.

n‑Butane has a higher boiling point. Its straight‑chain structure has a larger surface area, leading to stronger van der Waals forces between molecules. Iso‑butane, being branched, has a more compact shape, weaker intermolecular forces, and therefore a lower boiling point.

Explain why detergents are more effective than soaps for cleansing in hard water. Support your answer with relevant chemical equations.

Hard water contains Ca²⁺ and Mg²⁺ ions. Soaps are sodium/potassium salts of long‑chain fatty acids (e.g., RCOONa). They react with Ca²⁺/Mg²⁺ to form insoluble scum (e.g., (RCOO)₂Ca↓), reducing lather. Detergents are sodium salts of long‑chain alkyl sulphonic acids or alkyl benzene sulphonates (e.g., R‑SO₃Na). Their calcium/magnesium salts are soluble in water, e.g., 2R‑SO₃Na + Ca²⁺ → (R‑SO₃)₂Ca + 2Na⁺; (R‑SO₃)₂Ca remains soluble and forms lather. Hence detergents work well even in hard water.

Define a homologous series. Write any two characteristics of a homologous series with suitable examples.

A homologous series is a group of organic compounds having the same functional group and similar chemical properties, in which successive members differ by a –CH₂– unit. Characteristics: (i) All members can be represented by a general formula, e.g., alkanes have formula CₙH₂ₙ₊₂. (ii) The physical properties (such as melting/boiling points) show a gradual change with increasing molecular mass.

Using the concept of micelles, describe the cleansing action of soap. State the reason why soaps do not work well with hard water and explain how detergents overcome this limitation.

Soap molecules have a long hydrocarbon chain (hydrophobic tail) and an ionic head (hydrophilic). In water, they form micelles where tails attach to the oily dirt and heads face water, lifting dirt off the fabric. In hard water (containing Ca2+ and Mg2+ ions), soap forms insoluble scum and does not lather. Detergents are ammonium or sulphonate salts of long-chain carboxylic acids; their calcium/magnesium salts are soluble, so they work in hard water.

An organic compound 'X' is found in many antiseptic hand rubs. On heating with alkaline potassium permanganate, 'X' is oxidised to compound 'Y'. In the presence of a few drops of concentrated sulphuric acid, 'X' and 'Y' react together to form a sweet-smelling compound 'Z' which is used in making ice creams and perfumes. Identify X, Y and Z. Write the chemical equations for the reactions involved. Name the reaction that produces Z.

X = Ethanol (C2H5OH); Y = Ethanoic acid (CH3COOH); Z = Ethyl ethanoate (CH3COOC2H5). Reactions: (i) CH3CH2OH + 2[O] → CH3COOH + H2O (alkaline KMnO4); (ii) CH3COOH + C2H5OH ⇌ CH3COOC2H5 + H2O (conc. H2SO4). The reaction producing Z is called esterification.

Ethanol is a colourless liquid with a characteristic smell, widely used as a solvent and in alcoholic beverages. When ethanol is heated with alkaline potassium permanganate, it gets oxidized to ethanoic acid. The reaction is an oxidation process where the purple colour of potassium permanganate disappears as it is reduced. (1) Identify the functional group in ethanol and write its formula. (2) Write the chemical equation for the oxidation of ethanol to ethanoic acid. Mention the oxidizing agent used. (3) What happens to the colour of potassium permanganate during this reaction? Explain why.

Ethanol has an -OH functional group with formula C2H5OH. The oxidation equation is CH3CH2OH + 2[O] → CH3COOH + H2O using alkaline KMnO4 as the oxidizing agent. The purple colour of KMnO4 fades because it is reduced to colourless Mn2+ or MnO2.

Class 10 Science Chapter 4: Carbon and its Compounds — Important Questions & Sample Paper

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Yes — this page has 44+ original Class 10 Science Chapter 4 (“Carbon and its Compounds”) important questions with answers (Multiple Choice (MCQ), Assertion–Reason, Short Answer, Short Answer, Long Answer, Case Study). Practise them free, or generate a full CBSE board-pattern sample paper (80 marks) and export it to PDF or Word — in English & Hindi, for 2026-27.

This chapter explores the unique bonding properties of carbon, explaining why it forms millions of compounds. It begins with the electron dot structures and covalent bonding in carbon molecules like methane and CO2. Key concepts include catenation (self-linking ability) and tetravalency, which allow chains, branches, and rings. Students learn about allotropes of carbon—diamond, graphite, and fullerenes—and how their structures determine properties. The chapter introduces functional groups like alcohols, aldehydes, ketones, and carboxylic acids, and the concept of homologous series where successive members differ by CH2. Nomenclature rules for naming carbon compounds are covered. Chemical properties include combustion, oxidation (e.g., ethanol to ethanoic acid), addition reactions (hydrogenation), and substitution reactions. Important specific compounds are ethanol and ethanoic acid, along with their reactions: esterification, reaction with sodium, dehydration to ethene, and oxidation. Finally, soaps and detergents are discussed, including micelle formation and cleansing action. Exam questions often require drawing electron dot structures, identifying functional groups, naming organic compounds, writing balanced chemical equations, distinguishing between compounds based on reactions, and reasoning about why carbon forms so many compounds or why graphite conducts electricity. Sample questions include writing equations for reactions of ethanol/ethanoic acid, naming esters, identifying isomers, and solving identification puzzles based on properties.

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Science — Carbon and its Compounds

Class 10Time: 3 hrsMax Marks: 80

SECTION A

1.
Which equation correctly represents the reaction between ethanol and sodium?
(a) 2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂(b) C₂H₅OH + Na → C₂H₅Na + H₂O(c) 2C₂H₅OH + Na → C₂H₅OC₂H₅ + H₂(d) C₂H₅OH + 2Na → C₂H₄ + NaOH + H₂
1
2.
The IUPAC name of CH₃CHO is:
(a) Methanoic acid(b) Ethanol(c) Ethanal(d) Ethanoic acid
1
3.
An organic compound 'A' with molecular formula C₂H₆O, on heating with alkaline KMnO₄, gives compound 'B' which turns blue litmus red. 'A' is:
(a) Ethanol(b) Propanone(c) Ethanal(d) Propane
1

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Marks distribution & blueprint

In a CBSE exam, this chapter typically contributes questions across the following types. The last column shows how many original questions of each type we have ready in our bank for this chapter:

Question type	Marks each	In our bank
Multiple Choice (MCQ)	1 mark	13
Assertion–Reason	1 mark	6
Short Answer	2 marks	8
Short Answer	3 marks	6
Long Answer	5 marks	5
Case Study	4 marks	6

44 original, exam-style questions in our bank for this chapter — with answers.

Important & sample questions (with answers)

Real, exam-style questions to practise and revise — each with its answer. Generate a full paper for unlimited more.

Q1. Which equation correctly represents the reaction between ethanol and sodium?
1 mark
Multiple Choice (MCQ)
(A) 2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂(B) C₂H₅OH + Na → C₂H₅Na + H₂O(C) 2C₂H₅OH + Na → C₂H₅OC₂H₅ + H₂(D) C₂H₅OH + 2Na → C₂H₄ + NaOH + H₂
▸ Answer▾ Answer
2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂
Q2. The IUPAC name of CH₃CHO is:
1 mark
Multiple Choice (MCQ)
(A) Methanoic acid(B) Ethanol(C) Ethanal(D) Ethanoic acid
▸ Answer▾ Answer
Ethanal
Q3. An organic compound 'A' with molecular formula C₂H₆O, on heating with alkaline KMnO₄, gives compound 'B' which turns blue litmus red. 'A' is:
1 mark
Multiple Choice (MCQ)
(A) Ethanol(B) Propanone(C) Ethanal(D) Propane
▸ Answer▾ Answer
Ethanol
Q4. Soap molecules form micelles in water because they possess:
1 mark
Multiple Choice (MCQ)
(A) Only hydrophilic ends(B) Only hydrophobic ends(C) Both hydrophilic and hydrophobic parts(D) No ionic character
▸ Answer▾ Answer
Both hydrophilic and hydrophobic parts
Q5. Assertion (A): Saturated hydrocarbons are less reactive than unsaturated hydrocarbons. Reason (R): Saturated hydrocarbons contain only single bonds, while unsaturated hydrocarbons contain double or triple bonds.
1 mark
Assertion–Reason
(A) Both A and R are true and R is the correct explanation of A.(B) Both A and R are true but R is not the correct explanation of A.(C) A is true but R is false.(D) A is false but R is true.
▸ Answer▾ Answer
Both A and R are true and R is the correct explanation of A.
Q6. A compound with molecular formula C₄H₈ decolorizes bromine water. Draw all possible straight‑chain structural isomers of this compound. Write the addition reaction with hydrogen for any one of the isomers.
2 marks
Short Answer
▸ Answer▾ Answer
Straight‑chain isomers: but‑1‑ene (CH₂=CH‒CH₂‒CH₃) and but‑2‑ene (CH₃‒CH=CH‒CH₃). Addition reaction (for but‑1‑ene): CH₂=CH‒CH₂‒CH₃ + H₂ → CH₃‒CH₂‒CH₂‒CH₃ (in presence of Ni catalyst). The product is butane.
Q7. n‑Butane and iso‑butane have the same molecular mass but different boiling points. Which one has the higher boiling point? Explain your answer by relating the structure to intermolecular forces.
2 marks
Short Answer
▸ Answer▾ Answer
n‑Butane has a higher boiling point. Its straight‑chain structure has a larger surface area, leading to stronger van der Waals forces between molecules. Iso‑butane, being branched, has a more compact shape, weaker intermolecular forces, and therefore a lower boiling point.
Q8. Explain why detergents are more effective than soaps for cleansing in hard water. Support your answer with relevant chemical equations.
3 marks
Short Answer
▸ Answer▾ Answer
Hard water contains Ca²⁺ and Mg²⁺ ions. Soaps are sodium/potassium salts of long‑chain fatty acids (e.g., RCOONa). They react with Ca²⁺/Mg²⁺ to form insoluble scum (e.g., (RCOO)₂Ca↓), reducing lather. Detergents are sodium salts of long‑chain alkyl sulphonic acids or alkyl benzene sulphonates (e.g., R‑SO₃Na). Their calcium/magnesium salts are soluble in water, e.g., 2R‑SO₃Na + Ca²⁺ → (R‑SO₃)₂Ca + 2Na⁺; (R‑SO₃)₂Ca remains soluble and forms lather. Hence detergents work well even in hard water.
Q9. Define a homologous series. Write any two characteristics of a homologous series with suitable examples.
3 marks
Short Answer
▸ Answer▾ Answer
A homologous series is a group of organic compounds having the same functional group and similar chemical properties, in which successive members differ by a –CH₂– unit. Characteristics: (i) All members can be represented by a general formula, e.g., alkanes have formula CₙH₂ₙ₊₂. (ii) The physical properties (such as melting/boiling points) show a gradual change with increasing molecular mass.
Q10. Using the concept of micelles, describe the cleansing action of soap. State the reason why soaps do not work well with hard water and explain how detergents overcome this limitation.
5 marks
Long Answer
▸ Answer▾ Answer
Soap molecules have a long hydrocarbon chain (hydrophobic tail) and an ionic head (hydrophilic). In water, they form micelles where tails attach to the oily dirt and heads face water, lifting dirt off the fabric. In hard water (containing Ca2+ and Mg2+ ions), soap forms insoluble scum and does not lather. Detergents are ammonium or sulphonate salts of long-chain carboxylic acids; their calcium/magnesium salts are soluble, so they work in hard water.
Q11. An organic compound 'X' is found in many antiseptic hand rubs. On heating with alkaline potassium permanganate, 'X' is oxidised to compound 'Y'. In the presence of a few drops of concentrated sulphuric acid, 'X' and 'Y' react together to form a sweet-smelling compound 'Z' which is used in making ice creams and perfumes. Identify X, Y and Z. Write the chemical equations for the reactions involved. Name the reaction that produces Z.
5 marks
Long Answer
▸ Answer▾ Answer
X = Ethanol (C2H5OH); Y = Ethanoic acid (CH3COOH); Z = Ethyl ethanoate (CH3COOC2H5). Reactions: (i) CH3CH2OH + 2[O] → CH3COOH + H2O (alkaline KMnO4); (ii) CH3COOH + C2H5OH ⇌ CH3COOC2H5 + H2O (conc. H2SO4). The reaction producing Z is called esterification.
Q12. Ethanol is a colourless liquid with a characteristic smell, widely used as a solvent and in alcoholic beverages. When ethanol is heated with alkaline potassium permanganate, it gets oxidized to ethanoic acid. The reaction is an oxidation process where the purple colour of potassium permanganate disappears as it is reduced.
4 marks
Case Study
1. (i) Identify the functional group in ethanol and write its formula.1 mark
2. (ii) Write the chemical equation for the oxidation of ethanol to ethanoic acid. Mention the oxidizing agent used.2 marks
3. (iii) What happens to the colour of potassium permanganate during this reaction? Explain why.1 mark
▸ Answer▾ Answer
Ethanol has an -OH functional group with formula C2H5OH. The oxidation equation is CH3CH2OH + 2[O] → CH3COOH + H2O using alkaline KMnO4 as the oxidizing agent. The purple colour of KMnO4 fades because it is reduced to colourless Mn2+ or MnO2.

Frequently asked questions

How do I properly draw electron dot structures for carbon compounds like methane or CO2?

Start by showing the valence electrons of each atom. Carbon has four valence electrons, hydrogen one, oxygen six. Then pair the unpaired electrons to form shared pairs (covalent bonds) so that each atom achieves a stable electron configuration (octet for carbon and oxygen, duet for hydrogen). For methane, carbon shares its four electrons with four hydrogen atoms. For CO2, carbon shares two electrons with each oxygen atom, forming double bonds.

What are the key reactions of ethanol and ethanoic acid that frequently appear in CBSE exams?

For ethanol: reaction with sodium metal produces hydrogen gas and sodium ethoxide; dehydration with concentrated H₂SO₄ at 443 K gives ethene; oxidation with acidified K₂Cr₂O₇ yields ethanoic acid. For ethanoic acid: esterification with ethanol in the presence of concentrated H₂SO₄ forms an ester (ethyl ethanoate); reaction with sodium carbonate or sodium bicarbonate produces carbon dioxide gas; and saponification with sodium hydroxide forms soap.

How can I distinguish between ethanol and ethanoic acid using a simple chemical test?

Add sodium bicarbonate or sodium carbonate to both substances. Ethanoic acid reacts to produce brisk effervescence of carbon dioxide gas, while ethanol shows no reaction. Alternatively, use blue litmus paper: ethanoic acid turns it red, whereas ethanol does not change its color.

Why does carbon form a very large number of compounds? Give reasons with examples.

Carbon forms an immense variety of compounds due to two main reasons: catenation and tetravalency. Catenation is the ability of carbon atoms to bond with each other, forming long chains, branched chains, and rings (e.g., straight-chain alkanes like hexane and branched ones like isooctane). Tetravalency means carbon can form four covalent bonds with other atoms, including carbon, hydrogen, oxygen, and halogens, leading to countless structural and functional group variations.

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