Kerala Syllabus Class 9 Chemistry Chapter 8 Organic Chemistry Notes Solutions

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Kerala SCERT Class 9 Chemistry Chapter 8 Solutions Organic Chemistry

Kerala Syllabus Std 9 Chemistry Chapter 8 Organic Chemistry Notes Solutions Questions and Answers

Class 9 Chemistry Chapter 8 Let Us Assess Answers Organic Chemistry

Question 1.
The structural formula of a hydrocarbon is given below.

a. Write its condensed formula.
b. Write its molecular formula.
c. Draw the structure of the first compound of the homologous series to which this hydrocarbon belongs.
d. Write the IUPAC name of this compound.
Answer:
a.

b. C₄H₈

c. Ethene (C₂H₄) is the first compound.

d. Butene

Question 2.
C₂H₆, C₃H₈, ……………., C₅H₁₂ belong to the same homologous series.
a. Write the molecular formula of the missing compound.
b. Write the name of the homologous series to which these compounds belong.
c. Write the structural formula of C₂H₆.
Answer:
a. C₄H₁₀
b. Homologous series of alkanes
c. C₂H₆ is

Question 3.
Molecular formulas of some hydrocarbons are given below.
C₃H₈, C₄H₈, C₄H₁₀, C₃H₆
a. Which among these are alkanes?
b. What is the general formula of alkenes?
c. Write the molecular formula of alkyne having 4 carbon atoms.
Answer:
a. Alkanes – C₃H₈, C₄H₁₀
b. C_nH_2n
c. C₄H₆

Question 4.
a. Write the molecular formula of the missing compounds in the homologous series.

b. To which homologous series does category C belong?
c. Write the general formula of category A.
Answer:

b. Homologous series of alkynes
c. C_nH_2n

Question 5.
The molecular formulas of a few hydrocarbons are given below.
C₂H₄, C₂H₂, C₂H₆, C₃H₄, C₃H₈
a. Which among them belongs to the alkene group?
b. Which category does C₂H₂ belong to?
c. Which are the hydrocarbons having the general formula C_nH_2n+2?
Answer:
a. C₂H₄
b. Alkynes
c. C₂H₆ and C₃H₈

Question 6.
Two hints regarding a hydrocarbon are given below.
• It has 3 carbon atoms.
• The general formula of the category to which this hydrocarbon belongs is C_nH_2n+2.
a. Write the molecular formula and IUPAC name of this compound.
b. Draw the structure of this compound.
c. Write the molecular formula of the hydrocarbon having the same number of carbon atoms and having a double bond.
Answer:
a. Molecular formula – C₃H₈
IUPAC name – Propane

c. C₃ H₆

Question 7.
Hints about a cyclic compound are given below.
It has 6 carbon atoms and 12 hydrogen atoms.
a. Draw the structure of this compound.
b. Write the structural formula of the open chain hydrocarbon having the same molecular formula.
c. Write the molecular formula of the alkane having the same number of carbon atoms.
Answer:

c. C₆H₁₄

Question 8.
A chain having carbon atoms is given below.

a. Complete the structure by adding hydrogen atoms to each carbon atom. Write its IUPAC name also.
b. Write the molecular formula of this compound.
c. Draw the structure of a cyclic compound having the same molecular formula.
d. Write the IUPAC name of this cyclic compound.
Answer:
a. IUPAC Name – Pentene

b. C₅H₁₀

d. Cyclopentane

Question 9.
The molecular formula of an alicyclic compound is C₄H₈.
a. Write the structural formula of this compound.
b. Write the structural formula of the open-chain hydrocarbon having the same molecular formula.
Answer:
a. Alicyclic C₄H₈

b. Open chain C₄H₈

Question 10.
The structure of an alicyclic compound is given below.

a. What is its molecular formula?
b. Write its IUPAC name.
c. Write the structural formula of an open chain hydrocarbon having the same molecular formula.
Answer:
a. C₄H₆
b. Cyclobutene
c. Butyne

Question 11.
The molecular formula of a hydrocarbon is C₃H₆.
a. Write the structural formula of this compound.
b. To which category does it belong?
(Alkane, alkene, alkyne)
c. Draw the structure of an alicyclic compound having the molecular formula C₃H₆.
d. Write the IUPAC name of the compound.
Answer:

b. Alkene
c. Alicyclic C₃H₆

Question 12.
a. Write the molecular formula of naphthalene.
b. Draw the structure of naphthalene.
Answer:
a. C₁₀H₈
b. Naphthalene

Question 13.
What is the method used to separate the components from petroleum?
Butane, the main component of LPG, is an alkane. It has four carbon atoms. Write the structural formula of butane.
Answer:
a. Fractional distillation
b. Butane

Question 14.
a. Which among the following gases does not cause global warming? (Methane, carbon dioxide, nitrogen, nitrous oxide)
b. Write two ways to prevent global warming.
Answer:
a. Nitrogen

b. (i) Use public transportation whenever possible.
(ii) Reduce, Reuse, Recycle: This practice helps minimise waste and reduces the demand for new products, which often require energy-intensive manufacturing processes.
(iii) Reduce carbon emissions.

Extended Activities

Question 1.
Prepare and exhibit the ball and stick model of alkane, alkene and alkyne compounds having 4 carbon atoms.
Answer:
Hints
Alkane – Butane – C₄H₁₀
Alkene – Butene – C₄H₈
Alkyne – Butyne – C₄H₆

Question 2.
Present a seminar on the topic of “Global warming and climate change”.
Answer:
Hints: Include points like factors causing global warming, global warming and climate, consequences, and remedies.

Question 3.
Prepare and present a paper on the topic “The importance of Organic Chemistry”.
Answer:
Hints: Introduction – Define organic chemistry and its scope; body – Discuss the role of organic compounds in living organisms, explore the vast applications of organic chemistry in various industries, discuss the environmental implications of organic chemistry; conclusion – summarise the key points and emphasise the ongoing importance of organic chemistry.

Question 4.
The structural formula of a few organic compounds is given below.
i. CH₃-CH₂-OH
ii. CH₃-CH₂-CH₂-OH
a. Write the molecular formulae of these compounds.
b. Are they homologous? Substantiate your answer.
Answer:
a. i. – C₂H₅OH or C₂H₆O
ii. – C₃H₇OH or C₃H₈O

b. Yes, they are homologous. Ethanol (C₂H₆O) and propanol (C₃H₈O) differ by one -CH₂ unit, which is a key feature of homologous series.

Question 5.
Construct and exhibit a model of cyclic compounds having 6 carbon atoms.
Answer:
Hints

Organic Chemistry Class 9 Notes Questions and Answers Kerala Syllabus

Question 1.
Complete the table with the help of the periodic table.

Symbol	…………………………..
Atomic number	……………………………
Electronic configuration	………………………….
Valency	……………………………

Answer:

Symbol	C
Atomic number	6
Electronic configuration	2, 4
Valency	4

Carbon compounds are referred to as organic compounds due to their abundance and diversity
Carbon contains 4 electrons in its outermost shell and a valency of 4. This allows carbon to make covalent bonds in various ways.

Question 2.
The structure of an organic compound is given in the figure. What are the constituent atoms in this compound?

Answer:
Carbon and hydrogens.

Question 3.
What is the peculiarity of the bond between carbon and hydrogen?
Answer:
It is a single covalent bond, and in this bond, both carbon and hydrogen share electrons to achieve a stable electron configuration.

Question 4.
Do you know any other compounds that contain only carbon and hydrogen?
Answer:
Yes, there are a lot of other compounds that contain only carbon and hydrogen.

Question 5.
Look at the compounds given below. Complete the valency of carbon using hydrogen atoms.

Answer:

Question 6.
What are the peculiarities of the bond between carbon atoms?
Answer:
Three types of covalent bonds are present between these carbon atoms that are single, double and triple covalent bonds.
Hydrocarbons are compounds that contain only carbon and hydrogen

Question 7.
Analyse the structure of the given hydrocarbon.

a) Molecular formula?
b) What is the type of covalent bond in this compound?
Answer:
a) Molecular formula – CH₄
b) Single covalent bond

Question 8.
The structure of another hydrocarbon with two carbon atoms and having only a single bond between them is illustrated.

What is the molecular formula of this compound?
Answer:
C₂H₆ – ethane.

The structural formula of this compound can also be represented as CH₃—CH₂. Such a representation is known as a condensed formula.

Question 9.
Complete the table 8.2.

Answer:

The open-chain hydrocarbons having only single bonds between the carbon atoms are called alkanes.
n alkanes, since all the four valencies of each carbon atom are satisfied by single bonds, they are also known as saturated hydrocarbons.

Question 10.
Analyse Table 8.2 and answer the given questions.
a) How many hydrogen atoms are present in an alkane having one carbon atom? ……………….
b) How many hydrogen atoms are present in an alkane having 2 carbon atoms? ………………..
c) What if there are 3 or 4 carbon atoms? …………………
d) What number is added to twice the number of carbon atoms to get the number of hydrogen
atoms? ………………….
e) If an alkane contains an ‘n’ number of carbon atoms, how many hydrogen atoms will be
there? (2n, 2n+2,2n-2) ………………..
f) Write the general formula of alkanes ………………
Answer:
a) 4
b) 6
c) For 3 carbon atoms – 8 H atoms
For 4 carbon atoms – 10 H atoms
d) 2 is added
e) 2n+2
f) C_nH_2n+2

Question 11.
The structure of a hydrocarbon having a double bond between two carbon atoms is given

a) What is the molecular formula of the compound given above?
b) Write its condensed formula.
Answer:
a) C₂H₄
b)

Question 12.
Represent the structure of such hydrocarbons having a double bond between any of the two carbon atoms by adding more carbon atoms.
Answer:

Question 13.
Complete the table given below.

Answer:

Hydrocarbons having atleast one double bond between any two carbon atoms are called alkenes.

Question 14.
Analyse table 8.3
a) What is the relation between the number of carbon atoms and the number of hydrogen atoms in alkenes?
b) If an alkene contains an ‘n’ number of carbon atoms, how many hydrogen atoms will be there?
c) Write the general formula of alkenes.
Answer:
a) In alkenes, the number of hydrogen atoms is always twice the number of carbon atoms.
b) 2n
c) C_nH_2n

Question 15.
Look at the structure of a hydrocarbon having a triple bond between two carbon atoms.

a) Write the molecular formula of the compound given above.,
b) Write its condensed formula.
Answer:
a) C₂H₂
b) CH≡CH

Question 16.
Complete the table given below.

Hydrocarbons with atleast one triple bond between any two carbon atoms are called alkynes.
Answer:

Question 17.
Analyse table 8.4
a) In these, are the number of hydrogen atoms twice that of carbon atoms?
b) What number is subtracted from twice the number of carbon atoms to get the number of
hydrogen atoms in each of these?
c) If an alkyne has an ‘n’ number of carbon atoms, how many hydrogen atoms will be there? (2n+2, 2n, 2n-2)
d) Write the general formula of alkynes.
Answer:
a) No
b) 2
c) 2n-2
d) C_nH_2n-2

Question 18.
Analyse the molecular formula of the. hydrocarbons given below and classify them as alkane, alkene and alkyne.
C₅H₁₀, C₃H₄, C₂H₄, C₅H₁₂, C₆H₁₂, C₇H₁₂, C₉H₂₀, C₃H₈, C₄H₆, C₄H₈.
Answer

Alkane	Alkane	Alkane
C5H12, C9H20, C3H8	C5H10, C2H4, C6H12, C4H8	C3H4, C7H12, C4H6

Question 19.
Analyse the molecular formulae C₂H₆ and C₃H₈.
a) To which category do they belong?
(Alkane, alkene, alkyne)
b) What is the general formula of this category?
c) What is the difference between C₂H₆ and C₃H₈ in the number of carbon and hydrogen atoms? Let us examine.

Compound	Number of carbon atoms	Number of hydrogen atoms
C3H8 C2H6	3 2	8 6
Difference in the number of carbon and hydrogen atoms	1	……………………………..

d) Have you understood that the difference in the number of carbon and hydrogen atoms in these is -CH₂-?
e) Do C₄H₁₀ and C₅H₁₂, which belong to this category, have the same difference?
Answer:
a) Alkane
b) C_nH_{2n + 2}
c) There is a difference by -CH₂– group.

Compound	Number of carbon atoms	Number of hydrogen atoms
C3H8 C2H6	3 2	8 6
Difference in the number of carbon and hydrogen atoms	1	2

d) Yes
e) Yes, C₄H₁₀ and C₅H₁₂ also have a difference by -CH₂ group.

Question 20.
Alkene: C₆H₆ and C₄H₈
a) What is the difference in the number of carbon and hydrogen atoms in these alkenes?
b) The general formula of alkene ………………..
Answer:
a) There is a difference in 1 carbon and 2 hydrogens, i.e., a -CH₂– group.
b) C_nH_2n

Question 21.
Alkyne: C₂H₂ and C₃H₄
a) What is the difference in the number of carbon and hydrogen atoms in these alkynes?
b) The general formula of alkyne ……………..
Answer:
a) There is a difference in 1 carbon and 2 hydrogens, i.e., a -CH₂– group.
b) C_nH_2n-2
A homologous series is a series of organic compounds that can be represented by a general formula and have a difference of -CH₂– group between two successive members.

The characteristics of a homologous series are:
(i) The members can be represented by a general formula.
(ii) Successive members differ by a -CH2- group.
(iii) Members show similarity in chemical properties.
(iv) There is a regular gradation in their physical properties.

Question 22.
The molecular formulas of some hydrocarbons are given below.
C₂H₄, C₂H₆, C₃H₄, C₃H₈ .
a. Which of these compounds belong to the same homologous series?
b. Write the general formula of this homologous series.
Answer:
a. C₂H₆ and C₃H₈
b. C_nH_2n+2

Question 23.
The molecular formula of hydrocarbons that belong to the same homologous series are given below.
C₂H₂, C₃H₄, C₄H₆, A, B
a. Write the molecular formula of the compounds A and B.
b. To which category do these compounds belong?
(Alkane, alkene, alkyne)
c. What is their general formula?
d. Draw the structure of compound A.
Answer:
a. A – C₅H₈ and B – C₆H₁₀
b. Alkyne
c. C_nH_2n-2
d. C₅H₈

Question 24.
Write the IUPAC names of alkanes having 4 to 10 carbon atoms.
Answer:
C₄H₁₀ = Butane, C₅H₁₂ = Pentane, C₆H₁₄ = Hexane, C₇H₁₆ = Heptane, C₈H₁₈ = Octane, C₉H₂₀ = Nonane, C₁₀H₂₂ Decane.

Question 25.
Which is the suffix added here?
Answer:
“ene”.

Question 26.
Write the IUPAC names of alkenes having 4 to 10 carbon atoms.
Answer:
C₄H₈ = Butene, C₅H₁₀ = Pentene, C₆H₁₂ = Hexene, C₇H₁₄ = Heptene, C₈H₁₆ = Octene, C₉H₁₈ = Nonene, C₁₀H₂₀ = Decene.

Question 27.
Write the IUPAC names of alkynes having 4 to 10 carbon atoms.
Answer:
C₄H₆ = Butyne, C₅H₈ = Pentyne, C₆H₁₀= Hexyne, C₇H₁₂ = Heptyne, C₈H₁₆ = Octyne, C₉H₁₆ = Nonyne, C₁₀H₁₈ = Decyne

Question 28.
Notice the structure of a few carbon compounds given below.

What is the peculiarity of the structures of these carbon compounds?
Answer:
These carbon compounds are cyclic.
Carbon atoms can combine with one another to form cyclic compounds. Cyclic hydrocarbon compounds can be classified into two groups, namely alicyclic compounds and aromatic compounds.

Question 29.
The structure and IUPAC name of some alicyclic hydrocarbons are given. Write their molecular formula.

Answer:
Cyclobutane – C₄H₈, Cyclobutene – C₄H₆, Cyclopentene – C₅H₈, Cyclohexane – C₆H₁₂.

Question 30.
How are alicyclic compounds named?
Answer:
Alicyclic compounds can be named by adding the term ‘Cyclo-‘ as a prefix along with the IUPAC name of the hydrocarbon.

Question 31.
Write down the molecular formula of benzene.
Answer:
C₆H₆
Naphthalene is another aromatic hydrocarbon with a characteristic odour and a white crystalline form. Two benzene rings are fused together to form its structure. It is the main ingredient in mothballs. The structure of naphthalene is

Question 32.
Write the molecular formula of naphthalene.
Answer:
C₁₀H₈

Question 33.
The structural formula of a hydrocarbon is given below.
CH₂=CH-CH₂-CH₃
a. Write the molecular formula of this compound.
b. Draw the structure of a cyclic compound with the same molecular formula.
Answer:
C₄H₈
b. Cyclobutane

Question 34.
The structures of two organic compounds are given below. Compare these.

Answer:

	Compound A	Compound B
Molecular formula	C6H6	C6H12
IUPAC Name	Benzene	Cyclohexane
Aliphatic/ Aromatic	Aromatic	Alicyclic

Question 35.
You have seen that the number of carbon compounds is very high. List the reasons for this.
Answer:

• The valency of carbon is four. So, it has the ability to form four covalent bonds with other atoms or carbon itself.
• Ability for catenation.
• Can form single, double and triple covalent bonds.
• Can form an open chain and cyclic or ring compounds.

Question 36.
Which form of coal has the highest carbon content?
Answer:
Anthracite (94%).

Question 37.
Which form of coal has the lowest carbon content?
Answer:
Peat (57%).

Question 38.
What are the consequences of global warming? What are the ways to effectively counter global warming?
Answer:
Consequences

• Global warming is causing increasingly frequent and intense heatwaves, which threaten ecosystems and
• humans.
• Sea levels are rising faster as ice caps and glaciers melt, threatening coastal regions.
• Hurricanes, droughts, and floods are becoming more severe due to global warming, inflicting extensive damage and death.
• Many plant and animal species are losing habitat, endangering, and extinction due to climate change.

Ways to reduce

• Reduce the use of fossil fuels.
• Afforestation.
• Control deforestation.