Carbon and its Compounds Class 10 Important Questions with Answers Science Chapter 4

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Class 10 Science Chapter 4 Important Questions with Answers Carbon and its Compounds

Class 10 Chemistry Chapter 4 Important Questions with Answers Carbon and its Compounds

Carbon and its Compounds Class 10 Important Questions Very Short Answer Type

Question 1.
How many covalent bonds are there in a molecule of ethane, C₂H₆?
Answer:
There are seven covalent bonds in a molecule of ethane:

Question 2.
Write the electron dot structure of ethene molecule, C₂H₄. (2011 D)
Answer:
Electron dot structure of ethene molecule, C₂H₄:

or

Question 3.
Write the electron dot structure of ethane molecule, C₂H₆.  (2011 D)
Answer:
Electron dot structure of ethane, C₂H₆:

or

Question 4.
Draw the structure for ethanoic acid molecule, CH₃COOH.   (2011 OD)
Answer:
Ethanoic acid (CH₃COOH):

Question 5.
Draw the structure of hexanal molecule, C₅H₁₁CHO.   (2011 OD)
Answer:
Hexanal molecule, C₅H₁₁CHO:

Question 6.
Name the functional group present in each of the following organic compounds: (2011 D)
(i) C₂H₅Cl
(ii) C₂H₅OH
Answer:
Functional group present in:
(i) C₂H₅Cl – Chloro (halide)
(ii) C₂H₅OH – alccohol

Question 7.
Name the functional group present in each of the following compounds: (2012 D)
(i) CH₃COCH₃
(ii) C₂H₅COOH
Answer:

Organic compound	Functional group
(i) CH3COCH3	(>C = O) Ketonic group
(ii) C2H5COOH	( – COOH) Carboxylic acid

Question 8.
Which class of carbon compounds is responsible for the depletion of ozone layer at the higher level of the atmosphere? (2012 D)
Answer:
The depletion of ozone layer is due to the use of chemicals called chlorofluorocarbons.

Question 9.
Write the name and formula of the second member of the carbon compounds having functional group – OH. (2012 OD)
Answer:
Second member of alcohol family – C₂H₅OH (Ethanol)

Question 10.
Write the name and formula of the first member of the carbon compounds having functional group – COOH. (2012 OD)
Answer:
First member of carboxylic acid group is:
HCOOH – Methanoic acid.

Question 11.
Write the name and formula of the first member of the carbon compounds having functional group – CHO. (2012 OD)
Answer:
First member of Aldehyde group (–CHO) is Methanal/Formaldehyde, H – CHO.

Question 12.
Name the functional group present in each of the following compounds: (2012 D)
(i) HCOOH (ii) C₂H₅CHO
Answer:
Organic compound:
(i) HCOOH
(ii) C₂H₅CHO
Functional group:
Carboxylic acid ( –COOH)
Aldehyde (–CHO)

Question 13.
Write the name and formula of the 2^nd member of homologous series having general formula C_nH_2n. (2015 D)
Answer:
C_nH_2n : Alkene
Name : Propene (2^nd member)
Formula: C₃H₆

Question 14.
Write the name and formula of the 2^nd member of homologous series having general formula C_nH_2n+2. (2015 D)
Answer:
C_nH_2n+2 : Alkane series
Name : Ethane (2^nd member)
Formula: C₂H₆

Question 15.
Write the name and formula of the 2^nd member of homologous series having general formula (2015 D)
Answer:
C_nH_2n-2 : Alkynes
Name : Propyne (2^nd member)
Formula: C₃H₄

Question 16.
Write the number of covalent bonds in the molecule of ethane.  (2015 OD)
Or
How many covalent bonds are there in a molecule of ethane C₂H₆?  (2015 OD)
Answer:
Ethane – C₂H₆

No. of covalent bonds in ethane is 7.

Question 17.
Write the number of covalent bonds in the molecule of propane, C₃H₈. (2015 OD)
Answer:
Propane – C₃H₈

∴ No. of covalent bonds in propane is 10.

Question 18.
Write the number of covalent bonds in the molecule of butane, C₄H₁₀. (2015 OD)
Answer:
Butane – C₄H₁₀

∴ No. of covalent bonds in butane is 13.

Question 19.
Write the next homologue of each of the following: (2016 D)
(i) C₂H₄
(ii) C₄H₆
Answer:
(i) Next homologue of C₂H₄ is C₃H₆.
(ii) Next homologue of C₄H₆ is C₅H₈

Question 20.
Name the following compounds: (2016 D)
(i) CH₃ – CH₂ – OH;
(ii)

Answer:
(i) CH₃ – CH₂ – OH Ethanol
(ii)

Ethanal

Question 21.
Select saturated hydrocarbons from the following:  (2016 D)
C₃H₆; C₅H₁₀; C₄H₁₀; C₆H₁₄; C₂H₄
Answer:
Saturated hydrocarbons:
General formula = C_nH_2n+2
C₄H₁₀, C₆H₁₄

Question 22.
Write the name and structure of an alcohol with three carbon atoms in its molecule.  (2016 D)
Answer:
Name of an alcohol: Propanol
Structure of propanol: H₃C – CH₂ – CH₂ – OH
Or

Question 23.
Write the name and structure of an alcohol with four carbon atoms in its molecule. (2016 OD)
Answer:
Name of an alcohol: Butanol
Structure of butanol: CH₃ – CH₂ – CH₂ – CH₂OH
Or

Question 24.
Write the name and structure of an aldehyde with four carbon atoms in its molecule. (2016 OD)
Answer:
Name of an aldehyde: Butanal
Structure of Butanal: CH₃ – CH₂ – CH₂ – CHO
Or

Carbon and its Compounds Class 10 Important Questions Short Answer Type I

Question 1.
Name the main products formed when
(i) Ethanol is oxidised by an alkaline solution of KMnO₄.
(ii) Ethanol reacts with ethanoic acid.
(iii) Sodium ethanoate is heated with soda lime.
(iv) Ethanol is heated with cone. H₂SO₄ acid.
Answer:
(i) Ethanoic acid
(ii) Ethyl ethanoate
(iii) Methane (CH₄) gas
(iv) Ethene gas

Question 2.
(a) Write the chemical equation representing the preparation reaction of ethanol from ethene.
(b) Name the product obtained when ethanol is oxidised by alkaline potassium permanganate.
(c) Give an example of an esterification reaction.
Answer:
(a)

(b) Product with alkaline potassium permanganate is ethanoic acid.
(c)

Question 3.
What happens when ethanoic acid reacts with (i) magnesium, (ii) sodium carbonate, and (iii) sodium hydroxide? Write the necessary chemical equation in each case.
Answer:
(i) Magnesium ethanoate is formed

(ii) With sodium carbonate, it forms sodium ethanoate, CO₂ and H₂O

(iii) With sodium hydroxide, it forms sodium ethanoate and H₂O

Carbon and its Compounds Class 10 Important Questions Short Answer Type II

Question 1.
Write one chemical equation to represent each of the following types of reactions of organic substances: (i) Esterification (ii) Saponification (iii) Substitution   (2011 D)
Answer:
(i) Esterification: When ethanol reacts with ethanoic acid on warming in the presence of a few drops of conc. H₂SO₄, forms a sweet smelling ester, ethyl ethanoate.

(ii) Saponification. The alkaline hydrolysis of esters is known as saponification as this reaction is used for the preparation of soaps.

(iii) Substitution. The reaction, in which one (or more) hydrogen atoms of a hydrocarbon are replaced by some other atoms, is called substitution reaction.

Question 2.
What is an ‘esterification’ reaction? Describe an activity to show esterification. (2011 D)
Answer:
Carboxylic acid when reacts with alcohols in the presence of concentrated sulphuric acid to form pleasant smelling esters. This reaction is called esterification reaction.

The formation of esters from acid and an alcohol can be demonstrated by the following experiment:

Activity:

• About 2 – 3 ml of ethanol is taken in a test tube.
• About 2 – 3 ml of glacial acetic acid along with a few drops of concentrated sulphuric acid is added to the test tube.
• The reaction mixture is then heated in a water bath for two minutes.
• Now the contents are poured into a beaker containing 20 – 50 ml water. Notice the smell.
• We will observe sweet smell due to the formation of ester.

Question 3.
Write chemical equations for what happens when
(i) sodium metal is added to ethanoic acid.
(ii) solid sodium carbonate is added to ethanoic acid.
(iii) ethanoic acid reacts with a dilute solution of sodium hydroxide.
Answer:

Question 31.
Write chemical equations to show what happens when
(i) ethanol is heated with concentrated sulphuric acid at 443 K.
(ii) ethanol reacts with ethanoic acid in the presence of an acid acting as a catalyst.
(iii) an ester reacts with a base.
Answer:
(i) When ethanol is heated with concentrated sulphuric acid at 443K, it gets dehydrated to form ethene

(ii) When ethanol reacts with ethanoic acid on warming in the presence of a few drops of conc. sulphuric acid to form a sweet smelling ester, ethyl ethanoate

(iii) When an ester is heated with a base (sodium hydroxide) solution then the ester gets hydrolysed (breaks down) to form the parent alcohol and sodium salt of the carboxylic acid.

Question 4.
Describe two examples of different oxidations of ethanol. Name the products obtained in each case.  (2011 OD)
Answer:
(i) Ethanol bums readily in air with a blue flame to form carbon dioxide and water vapour and releasing a lot of heat and light.

(ii) When ethanol is heated with alkaline potassium permanganate solution or acidified potassium dichromate solution, it gets oxidised to ethanoic acid. It is also called controlled combustion.

Question 5.
What are isomers? Draw the structures of two isomers of butane, C₄H₁₀. Why can’t we have isomers of first three members of alkane series?  (2012 D, 2015 D)
Answer:
The organic compounds having the same molecular formula but different structures are known as isomers. Isomers of butane, C₄H₁₀:

Isomerism is not possible in first three members of alkane series (i.e., methane, ethane, propane) because they contain only one, two or three carbon atoms respectively and with only 1, 2 or 3 carbon atoms, it is not possible to have different arrangements of carbon atoms.

Question 6.
Complete the following equations:  (2011 D)
(i) CH₄ + O₂ →

(iii) CH₃COOH + NaOH →
Answer:
(i) CH₄ + 2O₂ → CO₂ + 2H₂O + Heat

(iii) CH₃COOH + NaOH → CH₃COONa + H₂O

Question 7.
Name the oxidising 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. (2012 OD, 2013 D)
Answer:
Acidified potassium dichromate K₂Cr₂O₇ or Alkaline KMnO₄ can be used as oxidising agent for the conversion of ethanol to ethanoic acid.

(i) Litmus test:

• If an organic compound (to be tested) does not change the colour of either of the litmus solution (blue or red) then the organic compound is neutral in nature. Ethanol is a neutral compound. It has no effect on any litmus solution.
• When some blue litmus solution is added to the organic compound (to be tested), if the blue litmus solution turns red; it shows that the organic compound is acidic and hence it is ethanoic acid.

(ii) Reaction with sodium carbonate:
When the organic compound (to be tested) is taken in a test tube and a pinch of sodium carbonate is added to it; if no reaction occurs in the reaction mixture, it is ethanol. No gas evolved when ethanol is treated with sodium hydrogen carbonate.

When the organic compound (to be tested) is taken in a test tube and a pinch of sodium carbonate is added to it; evolution of carbon dioxide with brisk effervescence shows that the given organic compound is ethanoic acid.
CH₃COOH + NaHCO₃ → CH₃COONa + CO₂ + H₂O

Question 8.
Write the name and the structural formula of the compound formed when ethanol is heated at 443 K with excess of conc. H₂SO₄. State the role of conc. H₂SO₄ in this reaction. Write chemical equation for the reaction. (2013 D)
Answer:
When ethanol is heated with excess of concentrated sulphuric acid at 443 K, it gets dehydrated to form ethene (an unsaturated hydrocarbon)

In this reaction, concentrated sulphuric acid acts as a dehydrating agent which removes water molecules from the ethanol molecule.

Question 9.
(a) Differentiate between alkanes and alkenes. Name and draw the structure of one member of each.
(b) Alkanes generally bum with clean flame. Why?  (2013 D)
Answer:
(a) Alkanes:

• An alkane is a hydrocarbon in which the carbon atoms are connected by only single covalent bond.
• General formula of alkane is C_nH_2n+2.
• The simplest alkane is methane (CH₄).
  
• Alkanes generally bum in air with a blue and non-sooty flame.
• Alkanes undergo substitution reactions.
• Alkanes do not decolourise red-brown colour of bromine water.

Alkenes:

• An alkene is an unsaturated hydro-carbon in which the two carbon atoms are connected by a double bond.
• General formula of alkene is C_nH_2n.
• The simplest alkene is ethene (C₂H₄).
  
• Alkenes burn in air with a yellow and sooty flame.
• Alkenes undergo addition reactions.
• Alkenes decolourise the bromine water.

(b) Alkanes burn in air with a blue and non-sooty flame because the percentage of carbon in the alkane is comparatively low which gets oxidised completely by oxygen present in air.

Question 10.
What happens when:   (2013 D)
(a) ethanol is burnt in air,
(b) ethanol is heated with excess cone. H₂SO₄ at 443 K,
(c) a piece of sodium is dropped into ethanol?
answer:
(a) Ethanol burns readily in air to form carbon dioxide and water vapour and releases a lot of heat and light.

(b) When ethanol is heated with excess of concentrated sulphuric acid at 170°C (443 K), it gets dehydrated to form ethene

(c) Ethanol reacts with sodium to form sodium ethoxide and hydrogen gas

Question 11.
A carboxylic acid C₂H₄O₂ reacts with an alcohol in the presence of H₂SO₄ to form a compound ‘X’. The alcohol on oxidation with alkaline KMnO₄ followed by acidification gives the same carboxylic acid, C₂H₄O₂. Write the name and structure of: (i) Carboxylic acid, (ii) alcohol and (iii) the compound ‘X’.  (2013 OD)
Answer:
Carboxylic acid, C₂H₄O₂:

(i) Carboxylic acid:
Name: CH₃COOH (Ethanoic Acid)
structure:

(ii) Alcohol: C₂H₅OH
Name: CH₃ – CH₂ – OH (Ethanol)
Structure:

(iii) Compound ‘X’: Easter
Name: CH₃COOC₂H₅ (Ethyl ethanoate)
Structure:

Chemical reactions:

Question 12.
What is meant by isomers? “We cannot have isomers of first three members of alkane series.” Give reason to justify this statement. Draw the structures of two isomers of pentane, C₅H₁₂. (2013 OD)
Answer:
The organic compounds having the same molecular formula but different structures are known as isomers. Isomers of first three members of alkane series are not possible because only one arrangement of carbon atoms is possible in their molecules.

Two isomers of pentane C₅H₁₂:

Question 13.
State the meaning of functional group in a carbon compound. Write the functional group present in:
(i) ethanol and (ii) ethanoic acid and also draw their structures.  (2014 D)
Answer:
An ‘atom’ or ‘a group of atoms’ which makes a carbon compound reactive and decides its properties (or functions) is called a functional group.
(i) Ethanol → Alcohol group (–OH)
(ii) Ethanoic acid → carboxylic acid group (–COOH)

Question 14.
Write the name and general formula of a chain of hydrocarbons in which an addition reaction with hydrogen can take place. Stating the essential conditions required for an addition reaction to occur write the chemical equation giving the name of the reactant and the product of such a reaction.   (2014 D)
Answer:
Addition reactions are a characteristic property of unsaturated hydrocarbons, i.e., Alkenes and Alkynes. General formula of Alkene: C_nH_2n, Alkyne: C_nH_2n-2
For example, Ethene undergoes addition reaction with hydrogen when heated in the presence of nickel catalyst to form ethane saturated hydrocarbon.

Thus addition of hydrogen to an unsaturated hydrocarbon gives a saturated hydrocarbon. This reaction is known as hydrogenation.

Question 15.
What are esters? How are they prepared? List two uses of esters. (2014 D)
Answer:
Esters are usually volatile liquids having pleasant smell (in fruity smell).
Preparation. When carboxylic acid reacts with an alcohol in the presence of a little concentrated sulphuric acid, it gives a pleasant smelling ester.

For example. When ethanoic acid is warmed with ethanol in the presence of a few drops of concentrated sulphuric acid, a sweet smelling ester called ethyl ethanoate is formed.

Uses:

• Esters are used in making perfumes.
• Esters are used in making artificial flavours and essences used in icecreams, sweets and cold drinks.

Question 16.
What are homologous series of carbon compounds? Write the molecular formula of two consecutive members of homologous series of aldehydes. State which part of these compounds determines their:
(i) physical and (ii) chemical properties.  (2013 D, 2014 OD)
Answer:
Homologous series. A series of carbon compounds in which the same functional group substitutes for hydrogen on a carbon chain is called a homologous series. There is a difference of –CH₂ in the molecular formulae of two nearest compounds of a homologous series. Each such series has same general molecular formula and has a general scientific name. There is a difference of 14 µ (unified mass) in the molecular masses of two nearest compounds of a series.

Members of homologous series of aldehydes:
H – CHO Methanal
CH₃ – CHO Ethanal
C₂H₅ – CHO Propanal

• The carbon-chain attached to aldehyde group, i.e., (H–, CH₃–, C₂H₅–) determine the physical properties.
• The functional group attached to all aldehydes (–CHO) determines the chemical properties.

Question 17.
What is meant by homologous series of carbon compounds? Write the general formula of (i) alkenes, and (ii) alkynes. Draw the structures of the first member of each series to show the bonding between the two carbon atoms. (2014 OD)
Answer:
Homologous series. A series of carbon compounds in which the same functional group substitutes for hydrogen on a carbon chain is called a homologous series. There is a difference of –CH₂ in the molecular formulae of two nearest compounds of a homologous series. Each such series has same general molecular formula and has a general scientific name. There is a difference of 14 µ (unified mass) in the molecular masses of two nearest compounds of a series.

General formula:

1. Alkenes, C_nH_2n
2. Alkynes, C_nH_2n-2

Structure:

• The first member of alkenes is ethene and its structure is
  
• The first member of alkynes is ethyne and its structure is H – C ≡ C – H

Question 18.
Define the term ‘structural isomerism’. Explain why propane cannot exhibit this property. Draw the structures of possible isomers of butane, C₄H₁₀.  (2014 OD)
Answer:

• The organic compounds having the same molecular formula but different structuresare known as structural isomers.
• The phenomenon of occurring two or more different organic compounds having the same molecular formula but different structures is called ‘structural isomerism’.
• No isomerism is possible in propane as it has only 3 carbon atoms, it is not possible to have different arrangement of carbon atoms in propane.
• Isomers of butane, C₄H₁₀:

Question 19.
List two reasons for carbon forming a large number of compounds. Name the type of bonding found in most of its compounds. Why does carbon form compounds mainly by this kind of bonding?
Give reason why the carbon compounds
(i) generally have low melting and boiling points.
(ii) do not conduct electricity in molten state.  (2014 OD)
Answer:
Carbon forms a large number of compounds.
The two properties of carbon which lead to the huge number of carbon compounds are:

1. Catenation. Catenation is the unique property of carbon atoms to form bonds with other atoms of carbon giving rise to large molecules.
2. Tetravalency. Since carbon has a valency of four, it is capable of bonding with four other atoms of carbon or atoms of some other monovalent elements.

Carbon compounds are formed mainly by covalent bonding, i.e., bond formed by sharing of electrons because Carbon atoms have 4 electrons in their outermost shell. So needs to gain or lose electrons to attain noble gas configuration. It could gain four electrons forming C^4- anion. But it would be difficult for the nucleus with six protons to hold on to ten electrons.

It could lose four electrons forming C⁴⁺ cation. But it would require a large amount of energy to remove four electrons from its outermost shell. Because of these reasons, carbon shares its valence electrons to complete its octet with other atoms to form covalent bonds.

Carbon compounds generally have low melting and boiling points because carbon compounds are generally formed by covalent bonds in which the force of attraction between their molecules is not very strong. Carbon compounds do not conduct electricity.

As carbon compounds have covalent bonds between them, these do not give rise to any ions in their solution form or molten state. So carbon compounds do not conduct electricity through them.

Question 20.
With the help of an example, explain the process of hydrogenation.   (2015 D)
Mention the essential conditions for the reaction and state the change in physical property with the formation of the product.
Answer:
Process of hydrogenation:

The addition of hydrogen to an unsaturated hydrocarbon to obtain a saturated hydrocarbon is called hydrogenation.

Essential conditions for the reaction are:

• Presence of an unsaturated hydrocarbon.
• Presence of a catalyst such as nickel (Ni) or palladium.

Changes observed:

• Change observed in the physical property is the change of unsaturated compound from the liquid state to saturated compound in solid state.
• The boiling or melting points of a product is increased.

Question 21.
What is the difference between the molecules of soaps and detergents, chemically? Explain the cleansing action of soaps. (2015 D, 2017 D)
answer:
Soaps:

1. Soaps are the sodium or potassium salts of long chain carboxylic acids.
   The ionic group in soaps is COO^– Na⁺
2. Soaps are biodegradable.
3. Soaps have relatively weak cleansing action.

Detergents:

1. Detergents are the sodium salts of long chain benzene sulphonic acids or ammonium salts of long chain carboxylic acids.
   The ionic group in a detergent is:
   –SO₃^– Na⁺ or –COO^– NH₄⁺
2. Some detergents are not biodegradable.
3. Detergents have a strong cleansing action.

Cleansing action of soaps:

Action of soap in removing an oily spot from a piece of cloth. Most of the dirt particles on skin or clothes are oily in nature. When a dirty cloth is put in water containing dissolved soap, the oil does not dissolve in water. The soap molecules are sodium or potassium salts of long chain carboxylic acids.

Soap has one polar end (the end with sodium or potassium ion) and one non-polar end (the end with fatty acid chain) as shown in the figure. The polar end is hydrophilic in nature, i.e., this end is attracted towards water. The non-polar is hydrophobic, but lipophilic in nature, i.e., attracted towards hydrocarbons, but not attracted towards water. When soap is dissolved in water, its hydrophobic end attach themselves to dirt and remove it from the cloth. First, the molecules of soap arrange themselves in micelle form and trap the dirt at the centre of the cluster.

The various micelles present in water do not come together to form a precipitate as each micelle repels the other because of the ion-ion repulsion. Thus, the dust particles remain trapped in micelles and are easily washed away with water. In this way soap micelles help in removing the dirt particles from the surface and this dirt dissolves in water and the surface gets cleaned and washed.

Question 22.
Write the name and structural formula of the compound obtained when ethanol is heated at 443K with excess of conc.H₂SO₄. Also write chemical eauation for the reaction stating the role of conc.H₂SO₄ in it. (2015 D, 2017 OD)
Answer:

Conc. H₂SO₄ acts as a dehydrating agent.

Question 23.
List two tests for experimentally distinguishing between an alcohol and a carboxylic acid and describe how these tests are performed.  (2015 OD)
Answer:
Test 1.
Litmus Test: Take 2 strips of blue litmus paper. Place a drop each of alcohol and carboxylic acid on these strips separately. The blue litmus paper turns red in the case of carboxylic acid and remains unaffected in the case of alcohol.

Test 2.
Sodium hydrogen carbonate Test/Sodium carbonate Test:
A pinch of sodium hydrogen carbonate or sodium carbonate is added to both alcohol and a carboxylic acid separately. If brisk effervescence with the evolution of a colourless gas is observed, it indicates the presence of carboxylic acid whereas no effervescence is seen in case of alcohol.

Question 24.
Draw the electron-dot structure for ethyne. A mixture of ethyne and oxygen is burnt for welding. In your opinion, why cannot we use a mixture of ethyne and air for this purpose? (2015 OD)
Answer:
In pure oxygen, ethyne undergoes complete combustion and high temperature suitable for welding is attained. Whereas air contains less percentage/amount of oxygen which results in incomplete combustion of ethyne and the temperature required for the welding is not attained.

Hence we cannot use a mixture of ethyne and air for this purpose.

Question 25.
What is meant by homologous series of carbon compounds? Classify the following carbon compounds into two homologous series and name them. (2015 OD)
C₃H₆, C₃H₆ C₄H₆, C₄H₈, C₅H₈, C₅H₁₀
Answer:
A homologous series is a group of organic compounds having similar structure and similar chemical properties in which the successive compounds differ by CH₂ group.

Question 26.
Write the name and general formula of a chain of hydrocarbons in which an addition reaction with hydrogen is possible. State the essential condition for an addition reaction. Stating this condition, write a chemical equation giving the name of the reactant and the product of the reaction.  (2015 OD)
Answer:
Addition of hydrogen is possible in Alkenes C_nH_2n and Alkynes C_nH_2n-2.
Addition reaction of unsaturated hydrocarbons occurs in the presence of catalysts such as nickel (Ni) or palladium (Pd) or platinum (Pt) to form saturated hydrocarbons.

Example, Ethene reacts with hydrogen when heated in the presence of nickel catalyst to form ethane.

Question 27.
What are covalent compounds? Why are they different from ionic compounds? List their three characteristic properties. (2016 D)
Answer:

• The chemical bond formed by the sharing of electrons between two atoms is known as a covalent bond. The molecules formed by sharing of electrons between two or more same atoms or between two or more non-metals are called covalent compounds.
• Covalent compounds are different from ionic compounds as ionic compounds are formed by transference of electrons.

Characteristics of covalent compounds:

• Covalent compounds usually have low melting and boiling points as they are formed by electrically neutral molecules. So, the force of attraction between the molecules of covalent compounds is very weak. Only a small amount of heat energy is required to break these forces.
• Covalent compounds are usually insoluble in water but they are soluble in organic solvents.
• Covalent compounds do not conduct electricity as they do not contain ions.

Question 28.
When ethanol reacts with ethanoic acid in the presence of cone. H₂SO₄ a substance with fruity smell is produced. Answer the following:  (2016 D)
(i) State the class of compounds to which the fruity smelling compounds belong. Write the chemical equation for the reaction and write the chemical name of the product formed.
(ii) State the role of cone. H₂SO₄ in this reaction.
Answer:
(i) Esters are the fruity smelling compounds.
Chemical equation:

(ii) Esterification takes place in the presence of catalyst concentrated H₂SO₄. It acts as a dehydrating agent, i.e., helps in the removal of water formed in the reaction between alcohol and carboxylic acid.

Question 29.
Name the compound formed when ethanol is heated is excess of cone, sulphuric acid at 443 K. Also write the chemical equation of the reaction stating the role of conc. sulphuric acid in it. What would happen if hydrogen is added to the product of this reaction in the presence of catalysts such as palladium or nickel? (2016 D)
Answer:
When ethanol is heated with excess of concentrated sulphuric acid at 170° C (443K) it gets dehydrated to form ethene (an unsaturated hydrocarbon).

In this reaction, concentrated sulphuric acid acts as a dehydrating agent which removes water molecule from the ethanol molecule.

If hydrogen is added to the ethene (product of the above reaction) in the presence of catalysts like palladium or nickel then one atom of H adds to each carbon atom of ethene due to which the double bond opens up to form a single bond in ethane.

Question 30.
What is an oxidising agent? What happens when an oxidising agent is added to propanol? Explain with the help of a chemical equation.  (2016 D)
Answer:

• The substance that supplies oxygen in a reaction for oxidation is called an oxidising agent. Examples of oxidising agents are potassium permanganate, potassium dichromate etc.
• When propanol is heated with alkaline potassium permanganate solution (or acidified potassium dichromate solution), it gets oxidised to propanoic acid.

Question 31.
Write the chemical equation of the reaction of ethanoic acid with the following:
(a) Sodium; (b) Sodium hydroxide; (c) Ethanol
Write the name of one main product of each reaction.
Answer:

Question 32.
An aldehyde as well as a ketone can be represented by the same molecular formula, say C₃H₆O. Write their structures and name them. State the relation between the two in the language of science. (2016 OD)
Answer:
Molecular formula: C₃H₆O

They are called isomers because both have same molecular formula but different structural formula (having different functional groups).

Question 33.
On dropping a small piece of sodium in a test tube containing carbon compound ‘X’ with molecular formula C₂H₆O, a brisk effervescence is observed and a gas ‘Y’ is produced. On bringing a burning splinter at the mouth of the test tube the gas evolved bums with a pop sound. Identify ‘X’ and ‘Y’. Also write the chemical equation for the reaction. Write the name and structure of the product formed, when you heat ‘X’ with excess cone, sulphuric acid.  (2016 OD)
Answer:
X = Ethanol = CH₃CH₂OH
or

Y = Hydrogen gas = H₂ ↑
When ethanol reacts with sodium it forms sodium ethoxide and hydrogen gas

When ethanol is heated with excess of conc. sulphuric acid, it gets dehydrated to

Question 34.
Write three different chemical reactions showing the conversion of ethanoic acid to sodium ethanoate. Write balanced chemical equation in each case. Write the name of the reactants and the products other than ethanoic acid and sodium ethanoate in each case. (2016 OD)
Answer:
1. When ethanoic acid reacts with sodium carbonate to form sodium ethanoate and CO₂.

2. When ethanoic acid reacts with sodium hydrogen carbonate it gives brisk effervescence of CO₂ gas and also forms sodium ethanoate.

3. When ethanoic acid reacts with sodium hydroxide (an alkali) it forms sodium ethanoate (salt) and water.

Question 35.
Complete the following chemical equations: (2017 D)
(i) CH₃COOC₂H₅ + NaOH →
(ii) CH₃COOH + NaOH →

Answer:

Question 36.
Write the structural formula of ethanol. What happens when it is heated with excess of cone. H₂SO₄ acid at 443K? Write the chemical equation for the reaction, stating the role of cone. H₂SO₄ acid in this reaction. (2017 OD)
Answer:
Structural formula of ethanol:

On heating ethanol with cone. H₂SO₄ acid ethene gas is produced.

Cone. H₂SO₄ acid acts as dehydrating agent which absorbs the released water.

Question 37.
Distinguish between esterification and saponification reactions with the help of chemical equations for each. State one use of each: (i) esters and (ii) saponification process. (2017 OD)
Answer:
(i) Esterification. In such a reaction an alcohol reacts with a carboxylic acid in the presence of cone. H₂SO₄ to form sweet smelling compounds called esters.

(ii) Saponification. In such a reaction an ester reacts with sodium hydroxide to form sodium salt of an acid and alcohol. It is a saponification reaction.

1. Esters are used for making of puddings and icecreams, etc.
2. Saponification process is used in making of various types of soaps.

Carbon and its Compounds Class 10 Important Questions Long Answer Type

Question 1.
(a) What is a soap? Why are soaps not suitable for washing clothes when the water is hard?  (2011 D)
(b) Explain the action of soap in removing an oily spot from a piece of cloth.
Answer:
(a) Soaps are sodium salts of fatty acids. Fatty acids are a type of carboxylic acids with long chain of carbon atoms.
Soaps are not suitable for washing clothes when the water is hard:

• The formation of lather is necessary for removing dirt from clothes during the washing of clothes. Soap does not give lather with hard water as it reacts with the calcium and magnesium ions present in hard water to form insoluble precipitates of calcium and magnesium salts of fatty acids.
• The scum (or precipitate) formed by the action of hard water on soap sticks to the clothes being washed and it interferes with the cleaning ability of soap. This makes the cleaning of clothes difficult.

(b)

Action of soap in removing an oily spot from a piece of cloth. Most of the dirt particles on skin or clothes are oily in nature. When a dirty cloth is put in water containing dissolved soap, the oil does not dissolve in water. The soap molecules are sodium or potassium salts of long chain carboxylic acids.

Soap has one polar end (the end with sodium or potassium ion) and one non-polar end (the end with fatty acid chain) as shown in the figure. The polar end is hydrophilic in nature, i.e., this end is attracted towards water. The non-polar is hydrophobic, but lipophilic in nature, i.e., attracted towards hydrocarbons, but not attracted towards water. When soap is dissolved in water, its hydrophobic end attach themselves to dirt and remove it from the cloth. First, the molecules of soap arrange themselves in micelle form and trap the dirt at the centre of the cluster.

The various micelles present in water do not come together to form a precipitate as each micelle repels the other because of the ion-ion repulsion. Thus, the dust particles remain trapped in micelles and are easily washed away with water. In this way soap micelles help in removing the dirt particles from the surface and this dirt dissolves in water and the surface gets cleaned and washed.

Question 2.
(a) In a tabular form, differentiate between ethanol and ethanoic acid under the following heads:
(i) Physical state (ii) Taste (iii) NaHCO₃ test (iv) Ester test
(b) Write a chemical reaction to show the dehydration of ethanol.
Answer:
(a)

(b) Dehydration of ethanol. When ethanol is heated with excess of conc. H₂SO₄ at 170°C, it gets dehydrated to form ethene (an unsaturated hydrocarbon).

Question 3.
(a) State two properties of carbon which lead to a very large number of carbon compounds.
(b) Why does micelle formation take place when soap is added to water? Why are micelles not formed when soap is added to ethanol?  (2011 OD)
Answer:
(a) The two properties of carbon which lead to a very large number of carbon compounds are:

1. Catenation. Catenation is the unique property of carbon atoms to form bonds with other atoms of carbon giving rise to large molecules.
2. Tetravalency. Since carbon has a valency of four, it is capable of bonding with four other atoms of carbon or atoms of some other monovalent elements.

(b) Soap molecules consist of two parts – one hydrophilic (ionic ends) and other hydrophobic (hydrocarbon chains). Hydrophobic part of soap is dissolved with dirt and hydrophilic remains suspended in water. Thus more molecules of soaps are attached to dirt having their one end suspended in water to form a micelle.
Since ethanol is not as polar as soap, micelle will not be formed in other solvents such as ethanol.

Question 4.
Explain isomerism. State any four characteristics of isomers. Draw the structures of possible isomers of butane, C₄H₁₀. (2011 OD)
Answer:
Isomerism. The existence of two or more different organic compounds having the same molecular formula but different structures is called isomerism.
Characteristics of isomerism:

1. Isomers have the same molecular formula but different structures.
2. In the phenomenon of isomerism, a given molecular formula can represent two or more different compounds.
3. Isomers of a given molecular formula have entirely different properties.
4. Isomerism is possible only with hydrocarbons having 4 or more carbon atoms.

Isomers of butane, C₄H₁₀:

Isomerism is not possible in first three members of alkane series (i.e., methane, ethane, propane) because they contain only one, two or three carbon atoms respectively and with only 1, 2 or 3 carbon atoms, it is not possible to have different arrangements of carbon atoms.

Question 5.
List in tabular form three physical and two chemical properties on the basis of which ethanol and ethanoic acid can be differentiated.  (2012 D)
Answer:
Ethanol:
Physical properties:

• It does not have any effect on either blue litmus or red litmus, therefore it is neutral.
• It has a burning taste.
• It has very low melting point (156 K) and low boiling point (351 K).

Chemical properties:

• Ethanol reacts with sodium (Na) metal vigorously to form sodium ethoxide and evolves H₂ gas (a gas which bums with a pop sound)
  2C₂H₅OH + Na → 2C₂H₅ONa + H₂ ↑
• Ethanol does not react with alkalies.

Ethanoic acid:
Physical properties:

• It turns blue litmus red, therefore it is an acid.
• It is sour in taste.
• It has moderate melting point (290 K) and boiling point (391 K).

Chemical properties:

• Ethanoic acid reacts with carbonates to from salt (sodium ethanoate) and releases CO₂ gas
  2CH₃COOH + Na₂CO₃ → 2C₂H₃COONa + CO₂ ↑ + H₂O
• Ethanoic acid reacts with alkalies to form its salt and water.

Question 6.
Ethanol is one of the most important industrial chemicals. It is used in medicine, to synthesize many important compounds, it is an excellent solvent.
However, inspite of its benefits it causes many social problems. If a person drinks alcohol regularly, he becomes an alcoholic. Alcohol is non-toxic but it produces physiological effects disturbing brain activity. These persons are also a threat to the lives of others.
(a) Give three reasons in favour and three reasons against ‘alcohol-free world’.
(b) ‘Alcohol drinking should not be portrayed on media.’ Give valid reasons to justify.   (2012 OD)
Answer:
(a) In favour of ‘Alcohol-free world’:

• Alcohol drinking lowers inhibitions which leads to increased violence and crime in the society.
• A liver disease ‘cirrhosis’ caused by alcohol can lead to death.
• Drunken driving leads to increased road accidents.

Against ‘Alcohol-free world’:

• Alcohol is used for making some medicines like cough syrups, tincture iodine, some tonics etc.
• Mixed with petrol, it is now being used as a fuel for light vehicles.
• It is used for making antifreeze material for cooling engines of vehicles.

(b) ‘Alcohol drinking should not be portrayed on media’ because young people and children are very much influenced by the media.

Question 7.
What is the difference between the chemical composition of soaps and detergents? State in brief the action of soaps in removing an oily spot from a shirt. Why are soaps not considered suitable for washing where water is hard? (2012 D)
Answer:
Difference between the chemical com position of soaps and detergents
Soaps:

• Soaps are sodium or potassium salts of some long chain carboxylic acids.
• Soaps do not form foam with hard water.
• Soaps are biodegradable substances.
• Soaps are mild cleansing agents.

Detergents:

• Detergents are generally ammonium or sulphonate salts of long chain carboxylic acids.
• Detergents form foam even with hard water.
• Detergents are non-biodegradable substances.
• Detergents are strong cleansing agents.

Cleansing action of soaps:

Action of soap in removing an oily spot from a piece of cloth. Most of the dirt particles on skin or clothes are oily in nature. When a dirty cloth is put in water containing dissolved soap, the oil does not dissolve in water. The soap molecules are sodium or potassium salts of long chain carboxylic acids.

Soap has one polar end (the end with sodium or potassium ion) and one non-polar end (the end with fatty acid chain) as shown in the figure. The polar end is hydrophilic in nature, i.e., this end is attracted towards water. The non-polar is hydrophobic, but lipophilic in nature, i.e., attracted towards hydrocarbons, but not attracted towards water. When soap is dissolved in water, its hydrophobic end attach themselves to dirt and remove it from the cloth. First, the molecules of soap arrange themselves in micelle form and trap the dirt at the centre of the cluster.

The various micelles present in water do not come together to form a precipitate as each micelle repels the other because of the ion-ion repulsion. Thus, the dust particles remain trapped in micelles and are easily washed away with water. In this way soap micelles help in removing the dirt particles from the surface and this dirt dissolves in water and the surface gets cleaned and washed.

Soaps are not considered suitable for washing when water is hard:
Soaps are sodium salts of fatty acids. Fatty acids are a type of carboxylic acids with long chain of carbon atoms.

Soaps are not suitable for washing clothes when the water is hard:

• The formation of lather is necessary for removing dirt from clothes during the washing of clothes. Soap does not give lather with hard water as it reacts with the calcium and magnesium ions present in hard water to form insoluble precipitates of calcium and magnesium salts of fatty acids.
• The scum (or precipitate) formed by the action of hard water on soap sticks to the clothes being washed and it interferes with the cleaning ability of soap. This makes the cleaning of clothes difficult.

Question 8.
What are hydrocarbons? Write the name and general formula of:   (2012 OD)
(i) saturated hydro-carbons,
(ii) unsaturated hydrocarbons, and draw the structure of one hydrocarbon of each type. How can an unsaturated hydrocarbon be made saturated?
Answer:
Hydrocarbons. A compound made up of hydrogen and carbon is called hydrocarbon. Petroleum is the most important natural source of hydrocarbon.

The general formula of saturated hydrocarbons or alkanes is C_nH_2n+2 where n is the number of carbon atoms in one molecule of the alkane.
Example: If an alkane has 1 carbon atom, then n = 1.
Molecular formula will be C₁H_2×1+2 = CH₄

An unsaturated hydrocarbon is a hydrocarbon in which the two carbon atoms are connected by a ‘double bond’ or a ‘triple bond’.
An unsaturated hydrocarbon in which the two carbon atoms are connected by a double bond is called an alkene.

General formula: C_nH_2n
Example: If n = 2     C₂H_2×2 = C₂H₄

An unsaturated hydrocarbon in which the two carbon atoms are connected by a triple bond is called an alkyne.
General formula: C_nH_2n-2
Example: If n = 2     C₂H_2×2-2 = C₂H₂
H – C ≡ C – H   Ethyne

An unsaturated hydrocarbon can be made saturated by the addition of hydrogen in the presence of nickel or palladium metal as catalyst

Question 9.
What are detergents chemically? List two merits and two demerits of using detergents for cleansing. State the reason for the suitability of detergents for washing, even in the case of water having calcium and magnesium ions. (2012 OD)
Answer:
Detergents are generally ammonium or sulphonate salts of long chain carboxylic acids.
A common detergent is sodium n-dodecyl benzene sulphonate.

Detergent can lather well even in hard water because they do not form insoluble calcium or magnesium salts with water. A detergent works by making the oil and grease particles of dirty clothes dissolve in water through the formation of miscelles.

• Merits of using detergents. Detergents are strong cleansing agents. Detergents form foam even with hard water.
• Demerits of using detergents. Detergents are non-biodegradable.

Question 10.
(a) Define the term ‘isomers’.
(b) Draw two possible isomers of the compound with molecular formula C₃H₆O and write their names.
(c) Give the electron dot structures of the above two compounds. (2013 D)
Answer:
(a) The organic compounds having same molecular formula but different structures, are known as isomers.

(b) Molecular formula – C₃H₆O
Two isomers:

(c) Electron dot structures:

Question 11.
An organic compound ‘X’ on heating with cone. H₂SO₄ forms a compound ‘Y’ which on addition of one molecule of hydrogen in the presence of nickel forms a compound ‘Z’. One molecule of compound ‘Z’ on combustion forms two molecules of CO₂ and three molecules of H₂O. Identify giving reasons the compounds ‘X’, ‘Y’ and ‘Z’. Write the chemical equations for all the chemical reactions involved. (2013 OD)
Answer:
Organic compound ‘X’ is ethanol, (i.e., CH₃ – CH₂OH).
When ethanol is heated with cone. H₂SO₄ it forms ‘Y’ which is ethene (CH₂ = CH₂).

Question 12.
State the reason why carbon can neither from C⁴⁺ cations C^4- anions, but forms covalent compounds. Also state reasons to explain why covalent compounds:
(a) are bad conductors of electricity?
(b) have low melting and boiling points? (2014 D)
Answer:
Carbon atoms have 4 electrons in their outermost shell. So needs to gain or lose electrons to attain noblegas configuration.

• It could gain four electrons forming C⁴⁺ anion. But it would be difficult for the nucleus with six protons to hold on to ten electrons.
• It could lose four electrons forming C^4- cation. But it would require a large amount energy to remove four electrons from its outermost shell.

Because of these reasons, carbon shares its valence electrons to complete its octet with other atoms to form covalent bonds.
(a) Covalent compounds are bad conductors of electricity because they do not contain ions.
(b) Covalent compounds have usually low melting and boiling points because they are made up of electronically neutral molecules. So the force of attraction between the molecules of a covalent compound is very weak. Only a small amount of heat energy is required to break these weak molecular forces, due to which covalent compounds have low melting and boiling points.

Question 13.
Elements forming ionic compounds attain noble gas configuration by either gaining or losing electrons from their outermost shells. Give reason to explain why carbon cannot attain noble gas configuration in this manner to form its compounds. Name the type of bonds formed in ionic compounds and in the compounds formed by carbon. Also give reason why carbon compounds are generally poor conductors of electricity.  (2014 OD)
Answer:
Carbon mainly forms covalent bonds because carbon atoms have 4 electrons in their outermost shell. So it needs to gain or lose electrons to attain noble gas configuration.

• It could gain four electrons forming C^4- anion. But it would be difficult for the nucleus with six protons to hold on to ten electrons.
• It could lose four electrons forming C⁴⁺ cation. But it would require a large amount of energy to remove four electrons from its outermost shell.

Because of these reasons, carbon shares its valence electrons to complete its octet with other atoms to form covalent bonds.
Carbon compounds are generally poor conductors of electricity because they are covalent in nature. A carbon atom has 4 valence electrons in it and all the 4 valence electrons of carbon are used up in sharing of with either carbon or with other atoms. So there are no free electrons and charge on carbon compounds.

Question 14.
Explain why carbon forms compounds mainly by covalent bond. Explain in brief two main reasons for carbon forming a large number of compounds. Why does carbon form strong bonds with most other elements?  (2015 D)
Answer:
The atomic number of carbon is 6 which means that a neutral atom of carbon retains 6 electrons. So, the electronic configuration of carbon is
K, L
2, 4
Since, carbon has 4 electrons in its outermost shell so, it should either lose or gain 4 electrons to achieve the inert gas configuration and become stable.

• It could gain four electrons forming C^4- anion. But it would be difficult for the nucleus with six protons to hold on to ten electrons due to inter electronic repulsion.
• It could lose 4 electrons forming C⁴⁺ cation. But it would require a large amount of energy to remove four electrons from its outermost shell.

Thus, it forms compounds mainly by covalent bonds.

Two properties of carbon which lead to huge number of carbon compounds are:

1. Catenation. Catenation is the unique property of carbon atoms to form bonds with other atoms of carbon giving rise to large molecules.
2. Tetravalency. Since carbon has a valency of 4, it is capable of bonding with 4 other atoms of carbon or atoms of some other monovalent element.

The reason for the formation of strong bonds by the carbon atoms is their small atomic size. Due to the small size of carbon atoms their nuclei hold the shared pairs of electrons between atoms strongly, leading to the formation of strong covalent bonds. The carbon atoms also form strong covalent bonds with the atoms of other elements such as hydrogen, oxygen, nitrogen, sulphur, chlorine and other elements.

Question 15.
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 OD, 2017 D)
Answer:
A soap is the sodium or potassium salt of a long chain carboxylic acid.
Example: C₁₇ H₃₅ COO^– Na⁺ Sodium stearate
C₁₅ H₃₁ COO^– Na⁺ Sodium palmitate

A detergent is ammonium or sulphonate salt of a long chain carboxylic acid.
Example: CH₃ – (CH₂)₁₁ – C₆H₄ – SO₃^– Na⁺
CH₃ – (CH₂)₁₀ – CH₂ – SO₄^– Na⁺

Cleansing action of soaps.

Action of soap in removing an oily spot from a piece of cloth. Most of the dirt particles on skin or clothes are oily in nature. When a dirty cloth is put in water containing dissolved soap, the oil does not dissolve in water. The soap molecules are sodium or potassium salts of long chain carboxylic acids.

Soap has one polar end (the end with sodium or potassium ion) and one non-polar end (the end with fatty acid chain) as shown in the figure. The polar end is hydrophilic in nature, i.e., this end is attracted towards water. The non-polar is hydrophobic, but lipophilic in nature, i.e., attracted towards hydrocarbons, but not attracted towards water. When soap is dissolved in water, its hydrophobic end attach themselves to dirt and remove it from the cloth. First, the molecules of soap arrange themselves in micelle form and trap the dirt at the centre of the cluster.

The various micelles present in water do not come together to form a precipitate as each micelle repels the other because of the ion-ion repulsion. Thus, the dust particles remain trapped in micelles and are easily washed away with water. In this way soap micelles help in removing the dirt particles from the surface and this dirt dissolves in water and the surface gets cleaned and washed.

Soaps are not suitable for washing clothes when the water is hard:

• The formation of lather is necessary for removing dirt from clothes during the washing of clothes. Soap does not give lather with hard water as it reacts with the calcium and magnesium ions present in hard water to form insoluble precipitates of calcium and magnesium salts of fatty acids.
• The scum (or precipitate) formed by the action of hard water on soap sticks to the clothes being washed and it interferes with the cleaning ability of soap. This makes the cleaning of clothes difficult.

Problems that arise due to the use of detergents instead of soaps:

1. Detergents are non-biodegradable, i.e., they cannot be decomposed by micro-organisms and hence cause water pollution in lakes and rivers.
2. Detergents can also cause skin problems.

Question 16.
(a) Give a chemical test to distinguish between saturated and unsaturated hydrocarbon.
(b) Name the products formed when ethane bums in air. Write the balanced chemical equation for the reaction showing the types of energies liberated.
(c) Why is reaction between methane and chlorine in the presence of sunlight considered a substitution reaction? (2016 D)
Answer:
(a) Bromine water test. The addition of bromine (Br₂) gives addition reactions with unsaturated compounds (like alkenes and alkynes). The addition of bromine is used as a test for unsaturated compounds. For this purpose, bromine is used in the form of bromine water. A solution of bromine in water is called bromine water. Bromine water has a red-brown colour due to the presence of bromine in it.

When bromine water is added to an unsaturated compound, then bromine gets added to the unsaturated compound and the red-brown colour of bromine water is discharged. So, if an organic compound decolourises bromine water, then it will be an unsaturated hydrocarbon (containing a double bond or a triple bond), but saturated hydrocarbon (alkanes) do not decolourise bromine water.

(b) When ethane burns in air, carbon dioxide and water vapours are formed along with heat and light.

This reaction is an exothermic reaction due to the evolution of heat.

(c) Methane reacts with chlorine in the presence of sunlight to form chloromethane and hydrogen chloride.

In this reaction, one ‘H’ atom of methane has been substituted (replaced) by a ‘Cl’ atom, converting CH₄ to CH₃Cl. Hence, it is considered a substitution reaction.

Question 17.
A carbon compound ‘P’ on heating with excess conc. H₂SO₄ forms another carbon compound ‘Q’ which on addition of hydrogen in the presence of nickel catalyst forms a saturated carbon compound ‘R’. One molecule of ‘R’ on combustion, forms two molecules of carbon dioxide and three molecules of water. Identify P, Q and R and write chemical equations for the reactions involved. (2016 OD)
Answer:

Explanation:
When ethanol is heated with excess of conc. H₂SO₄, it gets dehydrated to form ethene (an unsaturated hydrocarbon)

When ethene is heated with hydrogen in the presence of nickel catalyst it forms ethane (a saturated hydrocarbon)

CH₃ – CH₃ + \(\frac{7}{2}\)O₂ → 2CO₂ + 3H₂O + Heat + Light

Question 18.
Why are certain compounds called hydrocarbons? Write the general formula for homologous series of alkanes, alkenes and 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 equation to show the necessary conditions for the reaction to occur. (2017 OD)
Answer:
Hydrocarbons. As these compounds have only atoms of carbon and hydrogen elements in their molecules, so these are called Hydrocarbons.
General formulae:
Alkanes C_nH_2n+2
Alkenes C_nH_2n
Alkynes C_nH_2n-2

Structures of first member of each:

The reaction which converts Alkenes into Alkanes is called Addition Reaction.

Ni (Nickel) metal acts as catalyst in this reaction.