⚗️ Grade 9 Science · Chemistry

Samacheer Class 9 Science - Carbon and Its Compounds

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Complete Grade 9 Science questions and answers for Carbon and Its Compounds. Click any question to expand the answer.

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Carbon and its Compounds — key concepts & quick answers

What is catenation?
Catenation is the ability of carbon atoms to bond with one another to form long chains, branched chains and rings.
What are hydrocarbons?
Hydrocarbons are compounds made up of only carbon and hydrogen atoms — for example methane (CH₄) and ethane (C₂H₆).
What is the difference between saturated and unsaturated hydrocarbons?
Saturated hydrocarbons (alkanes) have only single bonds between carbon atoms; unsaturated hydrocarbons have one or more double bonds (alkenes) or triple bonds (alkynes).
What are functional groups? Give examples.
A functional group is an atom or group of atoms that gives an organic compound its characteristic properties — for example –OH (alcohol) and –COOH (carboxylic acid).
What is a homologous series?
A homologous series is a group of organic compounds with the same general formula and similar chemical properties, in which each member differs from the next by a –CH₂– unit.
📋 Sections in this chapter
I. Choose the Correct AnswerII. Fill in the BlanksIII. Match the FollowingIV. Answer BrieflyV. Answer in DetailVI. Higher Order Thinking SkillsIntext ActivitiesActivity – 1Activity – 2
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Your Progress — Carbon and Its Compounds0% complete
1I. Choose the Correct Answer6 questions

Q.1The phenomenon in which an element exists in different forms in same physical state is called
✓ Answer
  • (a) isomerism
  • (b) allotropy
  • (c) catenation
  • (d) crystallinity

Answer:
(b) allotropy


Q.2Carbon forms large number of organic compounds mainly due to
✓ Answer
  • (a) allotropy
  • (b) isomerism
  • (c) tetravalency
  • (d) catenation

Answer:
(d) catenation

Carbon’s tetravalency also contributes significantly.

Q.3Plastic container with resin code 5 is made of
✓ Answer
  • (a) Polystyrene
  • (b) PVC
  • (c) Polypropylene
  • (d) LDPE

Answer:
(c) Polypropylene


Q.4Polycarbonate (PC) and ABS plastics belong to resin code
✓ Answer
  • (a) 2
  • (b) 5
  • (c) 6
  • (d) 7

Answer:
(d) 7

Correction made:
Original answer incorrectly mentioned option (a).

Q.5Graphene is a one-atom-thick layer obtained from
✓ Answer
  • (a) diamond
  • (b) fullerene
  • (c) graphite
  • (d) gas carbon

Answer:
(c) graphite


Q.6Legal measures to prevent plastic pollution come under the ______ Protection Act.
✓ Answer
  • (a) Forest
  • (b) Wildlife
  • (c) Environment
  • (d) Human rights

Answer:
(c) Environment



2II. Fill in the Blanks5 questions

Q.1______ named carbon.
✓ Answer

Answer: Antoine Lavoisier


Q.2Buckminster Fullerene contains ______ carbon atoms.
✓ Answer

Answer: 60


Q.3Compounds with same molecular formula and different structural formula are known as ______.
✓ Answer

Answer: isomers


Q.4______ is a suitable solvent for sulphur.
✓ Answer

Answer: Carbon disulphide


Q.5There are ______ plastic resin codes.
✓ Answer

Answer: seven



3III. Match the Following0 questions
List IList II
AlkyneTriple bond
Andre GeimGraphene
(C_{60})Bucky Ball
ThermocolPolystyrene
CombustionOxidation


4IV. Answer Briefly5 questions

Q.1Differentiate Graphite and Diamond
✓ Answer
GraphiteDiamond
Each carbon forms 3 covalent bondsEach carbon forms 4 covalent bonds
Soft and slipperyExtremely hard
Layered hexagonal structureTetrahedral 3D structure
Conducts electricityPoor conductor of electricity
OpaqueTransparent
Correction made:
Diamond conducts heat well though it is electrical insulator.

Q.2Isomers of (C_4H_{10})
✓ Answer

(i) n-Butane

$$CH_3-CH_2-CH_2-CH_3$$

(ii) Iso-butane (2-Methylpropane)

$$CH_3-CH(CH_3)-CH_3$$

Q.3Why Does Carbon Form Covalent Compounds?
✓ Answer

Carbon forms covalent compounds rather than ionic compounds because of its electron configuration and the energy requirements involved in electron transfer. Carbon has four valence electrons in its outermost shell. To form ionic compounds, carbon would need to either lose all four electrons to form a C⁴⁺ ion or gain four electrons to form a C⁴⁻ ion. Both of these processes require extremely high amounts of energy because removing or adding four electrons is energetically unfavorable. Instead, carbon achieves a stable electron configuration by sharing electrons with other atoms through covalent bonding. By sharing electrons, carbon can complete its octet and achieve the stable electron configuration of neon without requiring the enormous energy needed for complete electron transfer. This is why carbon predominantly forms covalent compounds with other elements such as hydrogen, oxygen, nitrogen, and other carbon atoms, rather than forming ionic compounds.

Q.4Define Allotropy
✓ Answer

Answer:

Property by which an element exists in more than one form in same physical state is called allotropy.

Examples:

  • Diamond
  • Graphite
  • Fullerene

Q.5Why Are One-Time Plastics Harmful?
✓ Answer

Answer:

  • Cause environmental pollution
  • Block drains and water bodies
  • Harm animals and marine life
  • Produce toxic chemicals
  • Non-biodegradable

Examples:

  • Plastic carry bags
  • Cups
  • Straws
  • Food wrappers


5V. Answer in Detail3 questions

Q.1What is Catenation?
✓ Answer

Answer:

Catenation is property by which atoms of same element link together through covalent bonds.


Carbon and Catenation

  • Carbon atoms bond with one another repeatedly.
  • They form:
  • straight chains
  • branched chains
  • ring structures
  • This leads to enormous number of organic compounds.

Examples:

  • Starch
  • Cellulose
  • Hydrocarbons

Q.2Chemical Reactions of Carbon
✓ Answer

# (i) Oxidation / Combustion

Carbon reacts with oxygen.

$$C + O_2 \rightarrow CO_2 + \text{heat}$$

Incomplete combustion:

$$2C + O_2 \rightarrow 2CO$$

Methane Combustion

$$CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O + \text{heat}$$

# (ii) Reaction with Steam

$$C + H_2O \rightarrow CO + H_2$$

Mixture formed is called:

Water Gas


# (iii) Reaction with Sulphur

$$C + 2S \rightarrow CS_2$$

(Carbon disulphide)


# (iv) Reaction with Metals

Carbon forms carbides.

Example:

$$W + C \rightarrow WC$$

(Tungsten carbide)

Correction made:
Spelling corrected from “Tungesten”.

Q.3Safer Plastic Resin Codes
✓ Answer

Resin Code 2 — HDPE

  • Strong
  • Recyclable
  • Safer plastic

Resin Code 4 — LDPE

  • Flexible
  • Used in carry bags

Resin Code 5 — PP (Polypropylene)

  • Heat resistant
  • Safer for food storage


6VI. Higher Order Thinking Skills4 questions

Q.1Why Does Carbon Mostly Exist in Combined State?
✓ Answer

Answer:

Carbon readily forms compounds due to:

  • Catenation
  • Tetravalency
  • Multiple bonding
  • Isomerism
  • Allotropy

Hence carbon mainly occurs in combined form.


Q.2Why Is Burning Carbon Fuel in Poorly Ventilated Room Dangerous?
✓ Answer

Answer:

Incomplete combustion forms carbon monoxide.

$$2C + O_2 \rightarrow 2CO$$

Carbon monoxide:

  • binds with haemoglobin
  • reduces oxygen transport
  • may cause suffocation and death

Q.3Dioxins and PVC Plastics
✓ Answer

# Formation of Dioxins

Dioxins form during:

  • burning plastics
  • industrial processes
  • waste incineration

Especially when chlorine-containing materials burn.


# Linked Plastic

PVC (Polyvinyl Chloride)


# Harmful Effects

  • Cancer
  • Hormonal imbalance
  • Immune suppression
  • Reproductive disorders
  • Developmental defects

Q.4Which Plastic Bottle Should Yugaa Buy?
✓ Answer

Answer:

She should buy bottle with:

Resin Code 5

(Polypropylene)


Reason

  • Safer plastic
  • Heat resistant
  • Less toxic

Why Avoid Others?

Resin Code 1

Single-use plastic.


Resin Code 3

PVC — highly toxic.


Resin Code 7

Contains polycarbonate and BPA-related plastics.



7Intext Activities0 questions


8Activity – 10 questions

Organic and Inorganic Compounds

OrganicInorganic
Propane(CO_2)
KeroseneCO
Coconut oilMgO
Perfume(Na_2CO_3)
Alcohol(CaCO_3)
PetrolHCN
LPG
Correction made:
PVC is organic polymer, not inorganic.


9Activity – 20 questions

Fullerene and Football

Observation:

Football resembles Buckminster fullerene structure.

Contains:

  • 12 pentagons
  • 20 hexagons

Similar arrangement exists in:

$$C_{60}$$

(Buckminster fullerene)


# Important Summary


Allotropy

Different forms of same element.

Examples:

  • Diamond
  • Graphite
  • Fullerene

Catenation

Self-linking property of carbon.


Isomerism

Same molecular formula, different structures.


Graphene

Single layer of graphite.


Fullerene

Spherical carbon molecule.


Safer Plastics

Resin codes:

  • 2
  • 4
  • 5

Harmful Plastics

Resin codes:

  • 3
  • 6
  • 7

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