Chapter 4. Carbon and its Compounds

Class 10 Science Chapter 4. Carbon and its Compounds Internal Questions and Answers :

Internal Questions :

1. What would be the electron dot structure of carbon dioxide which has the formula  ?

Answer : The electron dot structure of carbon dioxide ( ) :

           
2. What would be the electron dot structure of a molecule of sulphur which is made up of eight atoms of sulphur? (Hint – The eight atoms of sulphur are joined together in the form of a ring.)

Answer : The electron dot structure of a molecule of sulphur ( ) :

    

Internal Questions :

1. How many structural isomers can you draw for pentane?

Answer :  There are three structural isomers of pentane .

(i)   n-pentane (normal pentane) :

   

(ii) 2-methylbutane (isopentane):

  

(iii) 2,2-dimethylpropane (neopentane):

     

2. What are the two properties of carbon which lead to the huge number of carbon compounds we see around us?

Answer :  The two properties of carbon that lead to the huge number of carbon compounds are:

(i) Catenation : Carbon has the unique ability to form bonds with other atoms of carbon, giving rise to large molecules. This property is called catenation.

(ii) Tetravalency : Carbon has a valency of four, it is capable of bonding with four other atoms of carbon or atoms of some other mono-valent element. This property is called tetravalency .

3. What will be the formula and electron dot structure of cyclopentane?

Answer : The molecular formula of cyclopentane is  .

     

4. Draw the structures for the following compounds.
(i) Ethanoic acid (ii) Bromopentane*
(iii) Butanone (iv) Hexanal.
*Are structural isomers possible for bromopentane?

Answer : (i) Ethanoic acid :

   

(ii) Bromopentane :

   

Yes, structural isomers are possible for bromopentane. Structural isomers are compounds that have the same molecular formula but different structural arrangements of atoms. For bromopentane (), the isomers arise from the different positions of the bromine atom on the pentane chain and the different ways the carbon chain can be arranged.

[ Types of Structural Isomers for Bromopentane:

Positional Isomers: These isomers differ in the position of the bromine atom on the pentane chain.

Chain Isomers: These isomers differ in the arrangement of the carbon chain (e.g., straight chain vs. branched chain).

Possible Structural Isomers of Bromopentane:

1-Bromopentane:

Bromine is attached to the first carbon of a straight pentane chain.

2-Bromopentane: 

Bromine is attached to the second carbon of a straight pentane chain.

3-Bromopentane: 

Bromine is attached to the third carbon of a straight pentane chain.

1-Bromo-2-methylbutane:

Bromine is attached to the first carbon of a branched pentane chain (2-methylbutane).

1-Bromo-3-methylbutane:

Bromine is attached to the first carbon of a branched pentane chain (3-methylbutane).

2-Bromo-2-methylbutane:

Bromine is attached to the second carbon of a branched pentane chain (2-methylbutane).

2-Bromo-3-methylbutane:

Bromine is attached to the second carbon of a branched pentane chain (3-methylbutane). ]
(iii) Butanone :

   

(iv) Hexanal :

  
5. How would you name the following compounds?

Answer : (i) Bromo-ethane

(ii) Methanal 

(iii) Hexyne

Internal Questions :

1. Why is the conversion of ethanol to ethanoic acid an oxidation reaction?

Answer : The conversion of ethanol to ethanoic acid is an oxidation reaction because oxygen is added to the ethanol molecule, and it results in the formation of a carboxylic acid (ethanoic acid). Oxidation involves gaining oxygen or losing hydrogen in a chemical reaction, which is precisely what happens in this conversion from ethanol to ethanoic acid. The camical equation is

 
2. A mixture of oxygen and ethyne is burnt for welding. Can you tell why a mixture of ethyne and air is not used?

Answer : A mixture of oxygen and ethyne is used for welding because it provides a higher flame temperature needed for welding metals effectively. Using a mixture of ethyne and air would result in a lower flame temperature, which would not be sufficient for welding applications.

Internal Questions :

1. How would you distinguish experimentally between an alcohol and a carboxylic acid?

Answer : The experimental tests to distinguish between an alcohol and a carboxylic acid are :

(i) pH Test (Litmus Paper or pH Meter):

Carboxylic Acid: Carboxylic acids are acidic and will turn blue litmus paper red. They typically have a pH less than 7.

Alcohol: Alcohols are generally neutral (pH ~7) and will not change the color of litmus paper.

(ii) Sodium Bicarbonate (NaHCO₃) Test :

Carboxylic Acid: Carboxylic acids react with sodium bicarbonate to produce carbon dioxide (CO₂) gas, which can be observed as effervescence (bubbling).

 

Alcohol: Alcohols do not react with sodium bicarbonate, so no effervescence will be observed.

(iii) Esterification Test

Carboxylic Acid: Carboxylic acids react with alcohols in the presence of an acid catalyst (e.g., concentrated sulfuric acid) to form esters, which often have a fruity smell.

Alcohol: Alcohols alone do not produce esters unless a carboxylic acid is present.

2. What are oxidising agents?

Answer : Alkaline potassium permanganate or acidified potassium dichromate are oxidising alcohols to acids, that is, adding oxygen to the starting material. This is known as oxidising agents.

Internal Questions :

1. Would you be able to check if water is hard by using a detergent?

Answer : Yes, we can check if water is hard by using a detergent. In hard water, the detergent will produce less lather and may leave behind a scum or residue. In contrast, in soft water, the detergent will produce more lather and effectively clean the clothes or dishes.
2. People use a variety of methods to wash clothes. Usually after adding the soap, they ‘beat’ the clothes on a stone, or beat it with a paddle, scrub with a brush or the mixture is agitated in a washing machine. Why is agitation necessary to get clean clothes?

Answer :  Agitation is necessary to remove dirt and stains from clothes effectively. When soap is added, it forms micelles that trap grease and dirt. However, mechanical action (beating, scrubbing, or washing machine agitation) helps loosen the dirt particles from fabric fibers. This movement ensures that soap micelles encapsulate dirt more efficiently and carry it away when rinsed, leading to cleaner clothes. Agitation also enhances soap penetration into fabric for better stain removal.

Class 10 Science Chapter 4. Carbon and its Compounds Exercise Questions and Answers :

1. 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.
2. Butanone is a four-carbon compound with the functional group
(a) carboxylic acid.
(b) aldehyde.
(c) ketone.
(d) alcohol.

Answer : (c) ketone.
3. 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.

4. Explain the nature of the covalent bond using the bond formation in  .

Answer :  A chemical bond which are formed by the sharing of an electron pair between two atoms are called covalent bond . Covalently bonded molecules are seen to have strong bonds within the molecule, but inter-molecular forces are small. Since the electrons are shared between atoms and no charged particles are formed, such covalent compounds are generally poor conductors of electricity.

   

In  , carbon (C) and hydrogen (H) atoms bond together by sharing electrons to form the molecule. Chlorine (Cl) also bonds with carbon by sharing electrons. This sharing creates a stable structure for the molecule, making it .

5. Draw the electron dot structures for
(a) ethanoic acid.
(b)  
(c) propanone.
(d)   .

Answer : (a) The electron dot structures for ethanoic acid.

(b)   The electron dot structures for

         
(c)  The electron dot structures for propanone.

      
(d)  The electron dot structures for  .

       

6. What is an homologous series? Explain with an example.

Answer : A series of compounds in which the same functional group substitutes for hydrogen in a carbon chain is called a homomlogous series .

Alkanes are a family of hydrocarbons with the general formula

Each member of this series has a carbon chain differs from the previous one by a group .

Methane -  

Ethane - 

Propane -   

Butane -

Pentane  -  

Hexane -

In this example, each alkane differs by a group, and they share similar chemical properties due to their structural similarity.

7. How can ethanol and ethanoic acid be differentiated on the basis of their physical and chemical properties?

Answer :   Physical Properties:

Ethanol ( ):

(i)  Colorless liquid at room temperature.

(ii) Slightly sweet smell.

(iii) Miscible in water in all proportions.

(iv)  Boiling point is 78.37°C.

(v)  Melting point is -114.1°C.

Ethanoic Acid (  ):

(i) Colorless liquid at room temperature.

(ii) Pungent, vinegar-like smell.

(iii)  Miscible in water in all proportions.

(iv) Boiling point is 118.1°C.

(v) Melting point is 16.6°C.

Chemical Properties:  Ethanol ()  :

(i)  Ethanol is a primary alcohol.

(ii) When ethanol burns in oxygen to give carbon dioxide , water and heat and light .

The reaction :  heat and light

(iii)  Reaction with acids : When ethanol react with hot acid (Con. Sulphuric acid) then produce ethene and water .

The reaction : 

Ethanoic Acid ( ) :

(i) Ethanoic acid is a carboxylic acid.

(ii) When ethanoic acid react with ethanol at presence of acid then produce ester .

The reaction :

(iii) Reaction with base : When ethanoic acid react with base ( ) then produce sodium acetate (salt) and water .

The reaction :

8. Why does micelle formation take place when soap is added to water? Will a micelle be formed in other solvents such as ethanol also?

Answer : Micelle formation takes place when soap is added to water because soap molecules have both hydrophilic (water-loving) and hydrophobic (water-repelling) parts. In water, the hydrophobic tails of soap molecules cluster together to avoid contact with water, while the hydrophilic heads face outward, interacting with the water molecules. This arrangement forms spherical structures called micelles, where the hydrophobic tails are shielded from water, and the hydrophilic heads are in contact with water.

9. Why are carbon and its compounds used as fuels for most applications?

Answer : Carbon and its compounds are used as fuels for most applications because they have high energy content, undergo combustion reactions to release energy, and are readily available in various forms such as coal, petroleum, and natural gas.

10. Explain the formation of scum when hard water is treated with soap.

Answer : When hard water is treated with soap, scum is formed because the soap reacts with the calcium and magnesium ions present in the hard water. These ions combine with the soap molecules and form insoluble compounds, which appear as a sticky, whitish substance known as scum. Scum reduces the effectiveness of the soap and makes it difficult to produce lather (foam), leading to the wastage of soap.

11. What change will you observe if you test soap with litmus paper (red and blue)?

Answer :  When you test soap with litmus paper, you will observe the following changes:

Red Litmus Paper → Turns blue, indicating that soap is basic in nature.

Blue Litmus Paper → Remains blue, confirming that soap is not acidic but alkaline (basic).

Soap is made from fatty acids and an alkali (like sodium hydroxide or potassium hydroxide), making it mildly basic in nature.

12. What is hydrogenation? What is its industrial application?

Answer : Unsaturated hydrocarbons add hydrogen in the presence of catalysts such as palladium or nickel to give saturated hydrocarbons . This process is called hydrogenation .

An important industrial application of hydrogenation is the production of hydrogenated oils or fats, used in the food industry to improve stability and texture in products like margarine and shortening.

13. Which of the following hydrocarbons undergo addition reactions:

            ,  ,   ,  and   .

Answer : The hydrocarbons that undergo addition reactions are (propene) and (ethyne).

(propene) is an alkene with a double bond between two carbon atoms, making it reactive to undergo addition reactions.

(ethyne) is an alkyne with a triple bond between two carbon atoms, making it also reactive to undergo addition reactions.

The other hydrocarbons, (ethane), (propane), and  (methane), are alkanes and do not have double or triple bonds, so they do not undergo addition reactions.

14. Give a test that can be used to differentiate chemically between butter and cooking oil.

Answer :  The saponification test can differentiate butter and cooking oil. Heat both with sodium hydroxide (NaOH); add a few drops of phenolphthalein. Cooking oil (unsaturated fat) reacts, forming soap and glycerol, while butter (saturated fat) shows minimal reaction. The disappearance of the pink color in cooking oil confirms its unsaturation.

15. Explain the mechanism of the cleaning action of soaps.

Answer : Soaps clean by forming micelles. A soap molecule has a hydrophilic (water-attracting) head and a hydrophobic (oil-attracting) tail. When mixed with water, the hydrophobic tails surround grease and dirt, breaking them into tiny droplets. The hydrophilic heads remain in water, allowing the dirt-laden micelles to be washed away. This emulsification process helps remove grease and grime effectively, leaving surfaces clean.