4. Carbon and Its Compounds Class 10 Science NCERT – Chapterwise Important Questions & Answers for CBSE Exam Preparation

Class 10 Science Chapter 4: Carbon and Its Compounds NCERT Important Questions and Answers for CBSE

Chapter 4: Carbon and Its Compounds

Multiple Choose Question and Answer :

Question: Ethane, with the molecular formula has
(a) 6 covalent bonds.
(b) 7 covalent bonds.
(c) 8 covalent bonds.
(d) 9 covalent bonds.

Answer: (b) 7 covalent bonds.

[ Ethane (C₂H₆) has a structure where two carbon atoms are joined by a single covalent bond, and each carbon atom forms bonds with three hydrogen atoms. So, counting the bonds: 1 C–C bond and 6 C–H bonds

Total = 1 + 6 = 7 covalent bonds  ]

Question: Butanone is a four-carbon compound with the functional group
(a) carboxylic acid.
(b) aldehyde.
(c) ketone.
(d) alcohol.

Answer:  (c) ketone.

[Butanone is a compound that contains a carbonyl group (C=O) attached to two carbon atoms, which is the defining feature of a ketone functional group.]
Question: While cooking, if the bottom of the vessel is getting blackened on the outside, it means that
(a) the food is not cooked completely.
(b) the fuel is not burning completely.
(c) the fuel is wet.
(d) the fuel is burning completely.

Answer: (b) the fuel is not burning completely.

[ When the bottom of the vessel gets blackened, it indicates the formation of soot (carbon particles). This happens when the fuel does not get enough oxygen and burns incompletely. So, the correct option is (b) the fuel is not burning completely. ]

Question: Acetic acid reacts with solid sodium hydrogen carbonate, [2013]

(a) Slowly forming no gas         (b) Vigorously with effervescence

(c) Slowly without effervescence      (d) Vigorouly without gas formation  

Answer: (b) Vigorously with effervescence .

[ Acetic acid reacts with sodium hydrogen carbonate to produce carbon dioxide gas, which is released with bubbles (effervescence), along with sodium acetate and water. The reaction is brisk.]

Question: Vapours of acetic acid smell : [2011]

(a) Pungent like vinegar     (b) Sweet like rose      (c) Suffocating like sulphur dioxide      (d) Odorless  like water

Answer: (a) Pungent like vinegar .

[ The vapors of acetic acid have a pungent smell, similar to vinegar. ]

Question:   A student takes  powder in a test tube and pours some drops of acetic acid in it. He observes : [2012]

(a) No reaction in the test tube

(b) Colourless gas with pungent smell

(c) Bubbles of a colourless and odourless gas

(d) White fumes with smell of vinegar .

Answer: (c) Bubbles of a colourless and odourless gas.

[ When acetic acid reacts with sodium carbonate, carbon dioxide gas is produced. This gas is colourless and odourless and is seen as bubbles (effervescence) in the test tube.]

Question: Hard water required for an experiment is not available in a school laboratory . However , following salts are available in the laboratory . Select the salts which may be dissolved in water to make it hard for the experiment . [2013]

 (i) Calcium Sulphate  (ii) Sodium Sulphate   (iii) Calcium Chloride  (iv) Potassium Sulphate   (v) Sodium Hydrogen Carbonate  (vi) Magnesium Chloride

(a) (i) , (ii) and (iv)    (b) (i) , (iii) and (vi)   (c) (iii) , (v) and (vi)  (d) (ii) , (iv) and (v)  

Answer: (b) (i) , (iii) and (vi)   

[ The salts that may be dissolved in water to make it hard for the experiment are: (i) Calcium Sulphate (iii) Calcium Chloride (vi) Magnesium Chloride ]

Question: We need 20% aqueous solution of sodium hydroxide for the study of saponification reaction . When we open the lid of the bottle containing solid sodium hydroxide we observe it in which form ? [2014]

(a) Colourless transparent beads     (b) Small white beads    (c) White pellets /flakes   (d) Fine white powder .

Answer: (c) White pellets/flakes .

[When the lid of the bottle containing solid sodium hydroxide (NaOH) is opened, it is typically observed in the form of white pellets or flakes. ]

Question A student takes 2 ml acetic acid in a dry test tube and adds a pinch of sodium hydrogen carbonate to it . He makes the following observations :  [2013]

(i) A colourless and odourless gas evolve with a brisk effervescence .

(ii) The gas turns lime water milky when passed through it .

(iii) The gas burns with an explosion when a burning splinter is brought neat it .

(iv) The gas extinguishes the burning splinter which is brought near it .

(a)  (i) , (ii)  and (iii)  (b) (ii) , (iii) and (iv)   (c) (iii) , (iv) and (i)  (d) (iv) , (i) and (ii)

Answer:  (b) (ii), (iii), and (iv)

[ Hard water contains calcium and magnesium ions. So, the salts that can make water hard must contain calcium or magnesium ions.

(i) Calcium Sulphate (CaSO₄) → Provides Ca²⁺ ions → Causes permanent hardness.

(iii) Calcium Chloride (CaCl₂) → Provides Ca²⁺ ions → Causes permanent hardness.

(vi) Magnesium Chloride (MgCl₂) → Provides Mg²⁺ ions → Causes permanent hardness. ]

Question: A student takes 2 ml acetic acid in a dry test tube and adds a pinch of sodium hydrogen carbonate to it . He makes the following observations :  [2013]

(i) A colourless and odourless gas evolve with a brisk effervescence .

(ii) The gas turns lime water milky when passed through it .

(iii) The gas burns with an explosion when a burning splinter is brought neat it .

(iv) The gas extinguishes the burning splinter which is brought near it .

(a)  (i) , (ii)  and (iii)  (b) (ii) , (iii) and (iv)   (c) (iii) , (iv) and (i)  (d) (iv) , (i) and (ii)

Answer: (d) (iv) , (i) and (ii)

[ Acetic acid reacts with sodium hydrogen carbonate to produce carbon dioxide gas, which is colourless and odourless and evolves with brisk effervescence. Carbon dioxide turns lime water milky and it extinguishes a burning splinter. It does not burn with an explosion. Hence, the correct option is (d) (iv), (i) and (ii). ]

Question: In an experiment to study the properties of ethanoic acid , a student takes about 3 mL of ethanoic acid in a dry test tube .He adds an equal amount of distilled water to it and shakes the test tube well . After some time he is likely to observe that [2014 1M]

(a)  a colloid is formed in the test tube    (b) the ethanoic acid dissolves readily in water    (c)the solution become light orange.   (d) water floats over the surface of ethanoic acid .

Answer: (b) the ethanoic acid dissolves readily in water.

[ Ethanoic acid is completely miscible in water, meaning it mixes uniformly in all proportions. When shaken with water, it dissolves readily and forms a clear homogeneous solution.]

Assertion (A) and Reason (R) Question and Answer:

Q21. Assertion (A) : In a homologous series of alcohols, the formula for the second member is and the third member is .

Reason (R) : The difference between the molecular masses of the two consecutive members of a homologous series is 144 .  [2020 1M]

(a) Both A and R are true and R is the correct explanation of the Assertion .

(b) Bothe A and R are true but R is not the correct explanation of the Assertion .

(c) A is true but R is false   

(d) A is false but R is true . 

Answer: (c) A is true but R is false.

[ In a homologous series of alcohols, the second member is C₂H₅OH (ethanol) and the third member is C₃H₇OH (propanol), so the Assertion is correct.

But the difference between consecutive members is due to a –CH₂– group, which corresponds to a mass difference of 14 u, not 144. So the Reason is incorrect. ]

Short Question and Answer :

Question: State two characteristic feature of carbon which when put together give rise to large number of carbon compounds . [1M]

Answer: Two characteristic features of carbon that, when combined, give rise to a large number of carbon compounds are tetravalency and catenation .

Question: What is hydrogenation? What is its industrial application? [2M]
Answer: Hydrogenation is a chemical reaction in which hydrogen is added to unsaturated compounds, such as vegetable oils, in the presence of a catalyst like nickel. This process converts unsaturated compounds into saturated ones by breaking double bonds and adding hydrogen atoms.

Industrial application: It is widely used in the food industry to convert vegetable oils, which are liquid, into solid or semi-solid fats, like in the production of margarine and shortening. This improves shelf life and texture of food products.

Question:  Explain the formation of scum when hard water is treated with soap. [2M]
Answer: Hard water contains calcium and magnesium ions. When soap is added to hard water, the soap reacts with these ions to form insoluble salts of calcium and magnesium. These insoluble substances appear as a sticky precipitate called scum. Because of this, soap does not lather easily in hard water and gets wasted in forming scum instead of cleaning.

Question: What is an homologous series? Explain with an example. [2M]
Answer: A series of compounds in which the same functional group substitutes for hydrogen in a carbon chain is called a homologous series. An example of an homologous series is the alkanes.

Alkanes are a family of hydrocarbons with the general formula:

Methane (CH₄), Ethane (C₂H₆), Propane (C₃H₈), and Butane (C₄H₁₀) are members of this series. Each successive compound differs by a –CH₂– unit, but all contain single bonds and show similar chemical behaviour.

Question: A compound ‘X’ on heating with excess conc. Sulphuric acid at 443K gives an unsaturated compound ‘Y’ . ‘X’ also reacts with sodium metal to evolve a colourless gas ‘Z’ . Identify ‘X’ , ‘Y’ and ‘Z’ . Write the equation of the chemical reaction of formation of ‘Y’ and also write the role of sulphuric acid in the reaction . [2018 2M]

Answer: Heating compound 'X' with excess concentrated sulphuric acid (​) at 443K produces an unsaturated compound 'Y'.

The compound 'X'  is (Ethanol) and the unsaturated compound ‘Y’ is  (Ethene)

The compound 'X' reacts with sodium metal (Na) to evolve a colorless gas 'Z'.

Sulphuric acid () acts as a dehydrating agent in this reaction.

Question: Why does micelle formation take place when soap is added to water? Will a micelle be formed in other solvents such as ethanol also? [3M]

Answer: Micelle formation occurs because soap molecules have two ends with different properties, one is hydrophilic which is water attracting and the other is hydrophobic which is water repelling. In water, the hydrophobic tails avoid water and cluster together while the hydrophilic heads remain in contact with water forming spherical structures called micelles. These micelles trap oily dirt in their interior and remain dispersed in water.

Micelles will not form in ethanol or similar solvents because soap molecules dissolve completely in such organic solvents instead of aggregating into micelles.

Question: How can ethanol and ethanoic acid be differentiated on the basis of their physical and chemical properties? [3M]

Answer:  Ethanol and ethanoic acid can be distinguished using both physical and chemical properties:

Physical properties:

(i) Odour: Ethanol has a mild, pleasant smell, while ethanoic acid has a strong vinegar-like smell.

(ii) Boiling point: Ethanoic acid has a higher boiling point than ethanol due to stronger intermolecular forces (hydrogen bonding).

Chemical properties:

(i) Litmus test: Ethanol does not change the colour of litmus paper, whereas ethanoic acid turns blue litmus red because it is acidic.

(ii) Reaction with sodium bicarbonate (NaHCO₃): Ethanoic acid reacts with sodium bicarbonate to produce carbon dioxide gas (effervescence), but ethanol does not show any such reaction.

Question: 3 mL of ethanol is taken in a test tube and warned gently in a water bath . A 5% solution of alkaline potassium permanganate is added first drop by drop to this solution , then in excess .

(i) How is 5% solution of prepared ?

(ii) State the role of alkaline potassium permanganate in this reaction . What happens on adding it in excess ?

(iii) Write  chemical equation of this reaction . [2020 3M]

Answer: (i) A 5% solution of KMnO₄ is prepared by dissolving 5 g of potassium permanganate in 100 mL of water.

(ii) Alkaline potassium permanganate acts as an oxidising agent. It oxidises ethanol to ethanoic acid. When added in excess, it ensures complete oxidation of ethanol.

(iii) Chemical equation:

Here, KMnO₄ provides oxygen for the oxidation reaction.

Question: Write chemical equations to show what happens when : [2011 3M]

(i) Ethanol is heated with concentrated sulphuric acid at 443K .

(ii) Ethanol reacts with ethanoic acid in the presence of an acid as a catalyst .

(iii) An ester reacts with a base .

Answer:  (i) When ethanol is heated with concentrated sulphuric acid at 443K ,then produces ethene and water .
 

(ii) When ethanol reacts with ethanoic acid in the presence of an acid () catalyst ,the produces ester .

(iii) When ester react with a base (NaOH) then produces ethanol and sodium acetate .

Question: Complete the following equations : [2012 3M]

(i)

(ii)

(iii)

Answer: (i)  heat and light  

(ii)

(iii)

Question: Name the oxidizing agent used for the conversion of ethanol to ethanoic acid . Distinguish between ethanol and ethanoic acid on the basis of :

(i) Litmus test      (ii) Reaction with sodium carbonate . [2013  3M]

Answer: The oxidizing agent used for the conversion of ethanol to ethanoic acid is  acidified potassium dichromate () and Alkaline permanganate () .

(i) Litmus test:

The distinguish between ethanol and ethanoic acid are :

Ethanol	Ethanoic acid
Ethanol is neutral and does not change the color of litmus paper.	Ethanoic acid is acidic and turns blue litmus paper red.

 (ii) Reaction with sodium carbonate:

Ethanol	Ethanoic acid
Ethanol does not react with sodium carbonate.	Ethanoic acid reacts with sodium carbonate to produce carbon dioxide gas, water, and sodium ethanoate.

Long Question and Answer :

Question: (i) State two properties of carbon which lead to a very large number of carbon compounds .

(ii) Why does micelle formation take place when soap is added to water ? why are micelles not formed when soap is added to ethanol ? [2011 5M]

Answer: (i) Two properties of carbon which lead to a very large number of carbon compounds are:

Tetravalency: Carbon has the ability to form four covalent bonds with other atoms due to its tetravalency. This allows carbon to form stable molecules with a wide variety of elements, including hydrogen, oxygen, nitrogen, and other carbon atoms.

Catenation: Carbon exhibits the unique property of catenation, which is the ability to form long chains or rings of carbon atoms by bonding with itself. This property allows carbon to form complex and diverse molecular structures, resulting in a vast array of organic compounds with different properties and functionalities.

(ii) Micelle formation takes place because soap molecules have two different ends, a hydrophilic head which is attracted to water and a hydrophobic tail which repels water. In water, the tails move away from water and come together, while the heads remain in contact with water, forming spherical structures called micelles.

Micelles are not formed in ethanol because soap dissolves completely in ethanol. Since ethanol can interact with both parts of the soap molecule, there is no need for the molecules to arrange themselves into micelles.

Question: Explain isomerism . State any four characteristics of isomers . Draw the structures of possible isomers of butane . [2011 5M]

Answer: Isomerism is the phenomenon in which compounds have the same molecular formula but different structural arrangements, leading to different properties.

Characteristics of isomers:

(i) They have the same molecular formula.

(ii) They have different structural formulae.

(iii) They show different physical properties like boiling point and melting point.

(iv) They may show different chemical properties due to different arrangement of atoms.

The structures of possible isomers of butane :

(a) n-butane (straight chain):  CH₃ – CH₂ – CH₂ – CH₃

(b) isobutane (branched chain or 2-methylpropane):
                    CH₃
                    |
          CH₃ – CH – CH₃

Question: List in tabular form three physical and two chemical properties on the basis of which ethanol and ethanoic acid can be differentiated . [2012 5M]

Answer: The three physical properties of ethanol and ethanoic acid are :

Ethanol	Ethanoic acid
(i) Ethanol is a colorless liquid at room temperature.	(i) Ethanoic acid is a colorless liquid at room temperature.
(ii) Ethanol has a characteristic pleasant odor.	(ii) Ethanoic acid has a pungent smell, reminiscent of vinegar.
(iii) Ethanol has a slightly sweet taste.	(iii) Ethanoic acid has a sour, acidic taste.

Two chemical differences between ethanol and ethanoic acid are:

Ethanol	Ethanoic acid
(i) Ethanol contains the hydroxyl functional group (– OH), which is characteristic of alcohols.	(i) Ethanoic acid contains the carboxyl functional group (– COOH), which is characteristic of carboxylic acids.
(ii) Ethanol is a neutral compound and does not exhibit acidic properties.	(ii) Ethanoic acid is a weak acid and can donate a hydrogen ion () in solution, thus exhibiting acidic properties.

Question: Both soap and detergent are some type of salts . What is the difference between them ? Describe in brief the cleansing action of soap . Why do soaps not form lather in hard water ? List two problems that arise due to the use of detergents instead of soaps . [2015 5M]

Answer:  Difference between Soap and Detergent are :

Soap	Detergent
(i) Soaps have a hydrophobic tail and a hydrophilic head, making them amphiphilic molecules.	(i) Detergents often have a similar structure but can be tailored for specific purposes.
(ii) Soaps are typically derived from natural sources, such as fats and oils .	(ii) Detergents are synthetic compounds.
(iii) Soaps form insoluble precipitates (scum) in hard water, reducing their effectiveness.	(iii) Detergents are less affected by hard water and can still produce lather.

Soap molecules have a hydrophilic head and a hydrophobic tail. In water, they form micelles where the tails trap oily dirt in the centre and the heads remain in water. This helps to wash away the dirt easily.
Hard water contains calcium and magnesium ions which react with soap to form insoluble scum. This prevents soap from forming lather.

Problems due to detergents:

(i) Many detergents are non-biodegradable and pollute water bodies.

(ii) They can harm aquatic life by forming persistent foam in water.

Question: A carbon compound ‘P’ on heating with excess conc.forms another carbon compound ‘Q’ which on nickel catalyst forms a saturated carbon compound ‘R’ . One molecules of ‘R’ on combustion form two molecules of carbon dioxide and three molecules of water . Identify P, Q and R and write chemical equations involved . [2016 5M]

Answer: P - (Ethanol) , Q - (Ethene) , R - (Ethane)

Chemical equations:

(i) Formation of Q from P :

(ii) Formation of R from Q :
 

(iii) Combustion of R :

 heat and light

Question: Why certain compound are called hydrocarbons ? Write the general formula for homologous series of alkanes , alkenes , alkynes and also draw the structure of the first member of each series . Write the name of the reaction that converts alkenes into alkanes and also write a chemical equations to show the necessary conditions for the reaction to occur . [2017 5M]

Answer: The carbon compounds which contain only carbon and hydrogen are called hydrocarbons.

The general formula for the homologous series of hydrocarbons are

The general formula of Alkane is  

Methane () :     

           H
            |
     H – C – H
            |
           H

The general formula of Alkene is

Ethene () :

     H     H
      |      |
H – C = C – H

The general formula of Alkyne is ​

Ethyne () :

 

The reaction that converts alkenes into alkanes is called hydrogenation.

In this reaction, hydrogen is added to the double bond of an alkene in the presence of a catalyst like nickel, palladium or platinum.

Chemical equation with condition: The chemical equation for the hydrogenation of ethene () to ethane () is :

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