Carbon and Its Compounds

Carbon, element number 6, is a widespread non-metal found everywhere from the atmosphere to all living things. It appears in pure forms like diamond, graphite, fullerenes, and coal, as well as in compounds such as carbon dioxide, carbonates, and hydrocarbons.

Its defining characteristics are catenation, the ability to form strong, diverse bonds with itself, and tetravalency, allowing it to create four stable bonds. Carbon also displays allotropy, existing in different physical forms: crystalline (diamond and graphite) and amorphous (coal, charcoal, coke, and lamp black).

Important carbon compounds include carbon dioxide (CO2​), an essential gas for life and a greenhouse gas, and carbon monoxide (CO), a highly toxic gas resulting from incomplete burning.

Exercise – I

Question 1.
Fill in the blanks.
(a) __________is present in both living and non-living things.

Ans : Carbon
(b) The tendency of an element to exist in two or more forms but in the same physical state is called _________.

Ans : Allotropy
(c)__________are the two major crystalline allotropes of carbon.

Ans : Crystalline and non-crystalline
(d)__________ is the hardest substance that occurs naturally.

Ans : Diamond
(e) The name ‘carbon’ is derived from the Latin word __________.

Ans : carbo

Question 2.
Choose the correct alternative.

(a) In a combined state, carbon occurs as
(i) coal
(ii) diamond
(iii) graphite
(iv) petroleum

Ans : petroleum

(b) A crystalline form of carbon is
(i) lampblack
(ii) gas carbon
(iii) sugar
(iv) fullerene

Ans : sugar

(c) Graphite is not found in
(i) Bihar
(ii) Maharashtra
(iii) Orissa
(iv) Rajasthan

Ans : Maharashtra

(d) Diamond is used for
(i) making the electrodes of electric furnaces.
(ii) making crucible for melting metals.
(iii) cutting and drilling rocks and glass.
(iv) making carbon brushes for electric motors.

Ans : cutting and drilling rocks and glass.

(e) Carbon forms innumerable compounds because
(i) it has four electrons in its outermost shell.
(ii) it behaves as metal as well as non-metal.
(iii) carbon atoms can form long chains.
(iv) it combines with other elements to form covalent compounds.

Ans : carbon atoms can form long chains.

Question 3.
Write ‘true’ or ‘false’ against the following statements.

(a) Carbon constitutes 0.03% of the earth’s crust. – True
(b) Graphite is the purest form of carbon. – False
(c) Coloured diamonds are costlier than colourless and transparent diamonds. – False
(d) Graphite has layers of hexagonal carbon bondings. – True
(e) Diamond is insoluble in all solvents. – True.

Question 4.
Define the following terms:
(a) Allotropy (b) Carat
(c) Crystal (d) Catenation
Answer:
(a) Allotropy: This is when an element can show up in different physical forms, like how carbon exists as both diamond and graphite, even though they’re made of the exact same stuff.

(b) Carat: For gems like diamonds, a ‘carat’ is just a measure of their weight. 

(c) Crystal: That’s a crystal, and it often has distinct flat surfaces and sharp corners.

(d) Catenation: This is carbon’s unique superpower – its ability to bond with itself to form really long chains or rings. It’s the main reason carbon can create such an incredible variety of compounds.

Question 5.
State the terms:

(a) Substances whose atoms or molecules are arranged in a definite pattern. – Crystals.
(b) Different forms of an element found in the same physical state. – Allotropy.
(c) The property by which atoms of an element link together to form long chain or ring compounds. – Catenation

Question 6.
Name the following:(a) The hardest naturally occurring substance. – Diamond.
(b) A greyish black non-metal that is a good conductor of electricity. – Graphite.
(c) The third crystalline form of carbon. – Fullerenes.

Question 7.
Answer the following questions:
(a) Why is graphite a good conductor of electricity but not diamond?
(b) Why is diamond very hard?
(c) What are fullerenes? Name the most common fullerenes.
(d) What impurity is present in black diamond?
(e) Explain the softness of graphite with reference to its structure.
Answer:
(a) Electrical Conductivity: Graphite conducts electricity because each carbon atom contributes one free, mobile valence electron.

(b) Diamond’s Hardness: Diamond is exceptionally hard due to its giant molecular structure. Each carbon atom forms strong bonds with four neighboring carbon atoms in a rigid tetrahedral arrangement.

(c) Fullerenes: Fullerenes represent a recently discovered, third crystalline form of carbon. They are found in both interstellar dust and Earth’s geological formations. 

(d) Black Diamonds: The characteristic color of black diamonds is attributed to the presence of copper oxide impurities.

(e) Graphite’s Softness: Graphite is soft because each carbon atom is linked to three neighbors, forming hexagonal layers. 

Question 8.
Give two uses of (a) graphite (b) diamond.
Answer:Uses of Graphite

Graphite is really versatile. We use it to make electrodes for electric furnaces because it conducts electricity well. It’s also excellent for crafting crucibles—those super-hot containers used to melt metals—thanks to its ability to withstand extreme temperatures.

Uses of Diamond

As for diamonds, their beauty makes them highly sought after for jewelry. Beyond their sparkle, their unmatched hardness makes them essential for cutting glass and drilling into rocks.

Question 9.
Write three differences between graphite and diamond.
Answer:

Feature	Diamond	Graphite
Structure	Crystalline, tetrahedral arrangement of carbon atoms, each bonded to four others.	Crystalline, layered structure of hexagonal rings of carbon atoms. Each carbon is bonded to three others within a layer.
Hardness	Extremely hard (hardest known natural substance).	Very soft, flaky, and slippery.
Electrical Conductivity	Excellent electrical insulator (does not conduct electricity).	Good electrical conductor (due to delocalized electrons between layers).
Appearance	Transparent and lustrous.	Opaque, dull gray/black.
Density	High (approx. 3.5 g/cm³).	Lower (approx. 2.2 g/cm³).
Uses	Jewelry, cutting tools, abrasives.	Lubricants, pencil leads, electrodes.

Exercise – II

Question 1.
Fill in the blanks:

(a) __________ is formed when charcoal is burnt in a limited supply of air.

Ans : Charcoal
(b) Coal is an _________ form of carbon.

Ans : amorphous
(c)_________ is the most inferior form of coal.

Ans : Peat
(d) Wood charcoal is a ________ conductor of heat and electricity.

Ans : bad
(e) ________ is used in making black shoe polish.

Ans : lampblack

Question 2.
Choose the correct alternative

(a) Anthracite is
(i) an inferior type of coal
(ii) a superior type of coal
(iii) a cheapest form of coal
(iv) none of above

Ans : a superior type of coal

(b) Destructive distillation of coal yields
(i) coal tar
(ii) coal gas
(iii) coke
(iv) all of the above

Ans : all of the above

(c) Lamp black is
(i) an amorphous form of carbon
(ii) a crystalline form of carbon
(iii) a pure form of carbon
(iv) a cluster of carbon atoms

Ans : an amorphous form of carbon

(d) The process by which decayed plants slowly convert into coal is called.
(i) petrification
(ii) carbonisation
(ii) carbonification
(iv) fermentation

Ans : carbonisation

(e) The purest form of the amorphous carbon is
(i) wood charcoal
(ii) sugar charcoal
(iii) bone charcoal
(iv) lampblack

Ans : sugar charcoal

Question 3.
Write ‘true’ or ‘false’ against the following statements:(a) Charcoal is a good absorbent. True
(b) Coke is obtained by destructive distillation of sugar. False
(c) Activated charcoal is a good conductor of electricity. False
(d) Wood charcoal is an important constituent of gun powder. True
(e) Coal gas is used in the preparation of artificial fertilisers. False.

Question 4.
Define the following:
(a) Carbonization
(b) Adsorption
(c) Bone black
Answer:
Carbonization: Carbonization is basically baking organic materials, like wood or coal, in an oven without any air. This process gets rid of all the gassy parts, leaving behind almost pure carbon, which we call charcoal or coke.

Adsorption: Think of adsorption as molecules from a gas or liquid simply clinging to the outside surface of a solid. It’s like how dust settles on a table—it’s on the surface, not absorbed all the way through the material.

Bone Black :Bone black is a unique kind of charcoal created by heating animal bones without oxygen. It’s a blend of carbon and a mineral found in bones called calcium phosphate. We often use it because it’s excellent at pulling colors out of liquids, especially in places like sugar factories.

Question 5.
Name the following:

(a) Substances whose atoms or molecules are not arranged in a geometrical pattern. – Amorphous
(b) The best variety of coal. – Bituminous
(c) The purest form of amorphous carbon. – Anthracite
(d) An amorphous form of carbon that contains about 98% carbon. – Anthracite
(e) Mixture of carbon monoxide and hydrogen. – Water gas.

Question 7.
Answer the following questions:
(a) What is destructive distillation? What are the products formed due to the destructive distillation of coal?
(b) Why is wood charcoal used in water filters and gas masks?
(c) How is wood charcoal made locally? What other substances are formed in the process.
(d) How many carbon atoms are there in Buckminster fullerenes?
Answer:
(a) Destructive Distillation: When coal is heated intensely without air, it breaks down into coke, coal tar, coal gas, and ammonia solution.

(b) Uses of Wood Charcoal: Wood charcoal’s porous structure makes it effective for adsorbing gases (useful in gas masks) and purifying water by removing impurities.

(c) Preparation of Wood Charcoal: Wood charcoal is made by heating wood with limited air to prevent full combustion. A common method involves stacking wood, covering it with clay to restrict air, and then igniting it for slow, incomplete burning, also producing wood tar and wood gas.

(d) Buckminsterfullerene: Also known as C₆₀, this is a distinct form of carbon consisting of 60 carbon atoms arranged in a stable, spherical shape resembling a soccer ball.

Question 8.
(a) Describe the formation of coal,
(b) Name four types of coal with percentage of carbon present in each, with uses.
Answer:
(a) Formation of Coal:
Coal was formed millions of years ago from the remains of dense forests and plants that once grew in swampy and low-lying areas. When these plants died, they got buried under layers of mud, sand, and sediments. Over time, due to high pressure and temperature deep within the Earth, and in the absence of air, these buried plant materials gradually changed into peat and eventually into coal.
This slow and natural process of coal formation is called carbonization.

(b) Types of Coal with Carbon Content and Uses:

1. Peat
   
   • Carbon Content: Around 60%
     
   • Use: It is the lowest grade of coal and is used as a fuel in some rural areas and for gardening (as soil conditioner).
     
2. Lignite (Brown Coal)
   
   • Carbon Content: About 60–70%
     
   • Use: Used mainly in thermal power stations to produce electricity.
     
3. Bituminous Coal
   
   • Carbon Content: Approximately 70–85%
     
   • Use: Most commonly used type of coal for domestic purposes, industrial heating, and electricity generation.
     
4. Anthracite
   
   • Carbon Content: Around 90–98% (highest among all types)
     
   • Use: Burns with very little smoke, making it ideal for home heating and in metallurgical processes like smelting of iron.

Question 9.
Name the products formed when:
(a) wood is burnt in the absence of air.
(b) bone is heated in the absence of air.
(c) diamond is burnt in air at 900°C.
(d) graphite is subjected to high pressure and 3000°C temperature.
Answer:
When wood is burned without air, you get charcoal, wood gas, and wood tar.

Heating bone in the absence of air yields bone char (also called animal charcoal) and some volatile matter.

If you burn diamond in air at 900°C, it turns into carbon dioxide.

Subjecting graphite to high pressure and a scorching 3000°C converts it into diamond.

Question 9.
Give two uses for each of the following:
(a) coal
(b) coke
(c) wood charcoal
(d) sugar charcoal
(e) bone charcoal
(f) lampblack
Answer:
(a) Coal We use coal mainly to fire up power plants for electricity. It’s also a key ingredient for making coke and coal gas.

(b) Coke Coke is crucial in metal extraction, especially for iron, where it acts as a strong reducing agent. It’s also burned as a fuel, particularly in blast furnaces.

(c) Wood Charcoal Great for grilling and barbecues, wood charcoal also works as an absorbent in gas masks and to purify water.

(d) Sugar Charcoal This type of charcoal is excellent for bleaching sugar solutions, and because it’s a very pure form of carbon, it’s used in some chemical processes.

(e) Bone Charcoal Mainly, bone charcoal is used in sugar refineries to clean up crude sugar solutions. It’s also good for pulling impurities out of other liquids.

(f) Lampblack Lampblack gives black inks, paints, and carbon paper their dark color. It’s also added to tires to make them stronger and last longer.

Question 10.
Give balanced equations for the following chemical reactions:
(a) wood charcoal and cone, nitric acid
(b) coke and steam
(c) wood charcoal and lead monoxide.
Answer:

Exercise – III

Question 1.
(a) Name the chemicals required for the preparation of carbon dioxide in the laboratory.
(b) How will you collect the gas?
(c) Write the balanced chemical equation for the above reaction.
(d) Draw a labelled diagram for the preparation of CO2 in the laboratory.
(e) Why is sulphuric acid not used for the preparation of carbon dioxide in the laboratory?
Answer:
(a) You’ll need marble chips (calcium carbonate) and dilute hydrochloric acid.

(b) Since carbon dioxide is heavier than air, you’d collect it by downward displacement of air.

(c) The balanced equation is: CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g)

(d) Laboratory preparation of carbon dioxide

(e)Sulfuric acid isn’t used because it forms calcium sulfate, which is insoluble. This calcium sulfate coats the marble chips, stopping the reaction very quickly.

Question 2.
Write the balanced chemical equations for the preparation of carbon dioxide by:
(a) heating calcium carbonate.
(b) the action of acetic acid on sodium bicarbonate.
(c) the action of dilute sulphuric acid on sodium bicarbonate.
Answer:

Question 3.
What happens when:
(a) a lit splinter is introduced into a jar containing carbon dioxide?
(b) moist blue litmus paper is placed in a jar containing carbon dioxide?
(c) carbon dioxide is passed through lime water first in small amounts and then in excess?
(d) a baking mixture containing baking powder is heated?
(e) a soda water bottle is opened?
Answer:
(a) Non-combustible/Extinguisher: The gas does not burn and may put out fires. 

(b) Acidic Gas: The gas has acidic properties.

 (c) Precipitate Formation and Redissolution: A solid initially appears, then dissolves again. 

(d) Reaction Product: This substance results from a chemical change. 

(e) Gas Effervescence (Depressurization): A gas, formerly held in solution by pressure, is bubbling out due to reduced pressure.

Question 4.
Give reasons for the following:
(a) An excess of carbon dioxide increases the temperature of the earth.
(b) Soda acid and foam types of fire extinguisher are not used for extinguishing electrical fires.
(c) Solid carbon dioxide is used for refrigeration of food.
Answer:
Climate Change: Too much carbon dioxide in the air traps heat, making the Earth warmer—this is known as the greenhouse effect.

Fire Safety: Never use soda acid or foam extinguishers on electrical fires. They contain water, which conducts electricity and can lead to electrocution or make the fire worse.

Dry Ice: Dry ice is ideal for cooling food because it’s very cold and turns directly into gas, leaving no messy liquid behind.

Question 5.
What is a fire extinguisher? What is the substance used in the modern type of fire extinguishers? How is it an improvement over the soda acid-type and the foam-type fire extinguishers?
Answer:
Modern fire extinguishers are a significant improvement over older soda-acid and foam models due to several key factors. They offer greater versatility, with types like “ABC” dry chemical extinguishers capable of tackling a broader range of fire classes (A, B, and C). Carbon dioxide (CO2​) extinguishers are also effective for Class B and C fires, and importantly, they leave no residue, minimizing damage to sensitive equipment. Even dry chemical agents, while leaving residue, are far less corrosive than older solutions. Modern designs also prioritize user-friendliness and simpler maintenance. Crucially, they are more efficient, rapidly suppressing fires by interrupting chemical reactions or displacing oxygen, leading to quicker and more effective fire control.

Question 6.
Explain the term ‘greenhouse effect’. How can it be both beneficial and harmful for life on earth ?
Answer:
The greenhouse effect is Earth’s inherent warming process, analogous to a greenhouse retaining solar heat. Specific atmospheric gases, such as carbon dioxide, methane, and water vapor, permit sunlight to enter but absorb some of the outgoing thermal radiation.

This vital mechanism renders Earth habitable, preventing it from becoming a frozen world. Nevertheless, human activities, particularly the combustion of fossil fuels and the clearing of forests, are intensifying this effect by releasing excessive amounts of more greenhouse gases. This amplified, or “enhanced,” greenhouse effect traps additional heat, leading to global warming and climate change. The consequences include rising ocean levels, extreme weather events, disturbances to ecosystems, and threats to human health and food supply.

Question 7.
What steps should be taken to balance carbon dioxide in the atmosphere ?
Answer:
Tackling climate change requires a multi-pronged approach. First and foremost, we must drastically cut emissions by shifting from fossil fuels to renewables like solar, wind, and hydro, alongside boosting energy efficiency and promoting eco-friendly transport. Secondly, strengthening natural carbon absorbers is vital – this means planting new forests, protecting existing ones, and adopting land management practices that enrich soil carbon. While still evolving, carbon capture and storage technologies can help decarbonize stubborn industrial sectors. Finally, success hinges on robust policy, international collaboration, and individual efforts to drive these essential changes.

Question 8.
State three ways by which carbon dioxide gas is added into the atmosphere.
Answer:

1. Combustion of fossil fuels: Burning coal, oil, and natural gas for energy production (e.g., electricity, transportation, manufacturing) liberates stored carbon as carbon dioxide.
2. Deforestation: The destruction or burning of forests releases carbon previously sequestered in trees, and reduces the Earth’s capacity to absorb atmospheric CO2.
3. Volcanic activity: Volcanic eruptions discharge substantial quantities of carbon dioxide and other gases from the Earth’s interior into the air.

Exercise – IV

Question 1.
Fill in the blanks:

(a) _________ is formed when carbon is burnt in a limited supply of air or oxygen.

Ans : Carbon monoxide
(b) Carbon monoxide bums in air with a _________ flame to form carbon dioxide.

Ans : pale blue
(c) Carbon monoxide is a product of___________ combustion.

Ans : incomplete
(d) A mixture of 95% oxygen and 5% carbon dioxide is called ________

Ans : carbogen
(e) Carbon dioxide is used as a ___________in the extraction of pure metals from their corresponding ores.

Ans : reducing agent 

Question 2.
Match the following.

Answer:

Question 3.

Question 3.
How is carbon monoxide gas formed?
Answer:
When fuels like wood, coal, or gas burn with insufficient oxygen, they generate carbon monoxide (CO) instead of carbon dioxide (CO2​). This “incomplete combustion” usually happens in confined areas or due to malfunctioning appliances, resulting in the production of this poisonous gas.

Question 4.
State the poisonous nature of carbon monoxide?
Answer:
Carbon monoxide is a lethal, unseen gas that harms the body by binding to hemoglobin in red blood cells. This crucial attachment stops oxygen from reaching your organs and tissues. Without oxygen, cells can suffer severe damage, leading to illness or even death, particularly with significant or long-term exposure.

Question 5.
Give two uses of carbon monoxide.
Answer:
Carbon monoxide is crucial in industry for two primary uses:

• Chemical Manufacturing: It’s a key ingredient in making chemicals such as acetic acid.
• Metal Refining: It’s used to purify metals, particularly nickel, through processes like the Mond process.

Question 6.
Why is carbon monoxide called a silent killer?
Answer:
Carbon monoxide (CO) is known as a “silent killer” because it’s an invisible, odorless, and tasteless gas, making it impossible to detect without a CO detector. It’s deadly because it binds to hemoglobin in red blood cells much more readily than oxygen, forming carboxyhemoglobin. This prevents oxygen from being delivered to the body’s tissues and organs, leading to cellular suffocation. Victims often experience symptoms like headache, dizziness, nausea, and confusion, which can easily be mistaken for the flu or other common ailments, further delaying recognition and treatment. Unconsciousness and death can occur rapidly, often without the victim realizing they are being poisoned.

Question 7.
Explain the reducing action of carbon monoxide.
Answer:
Carbon monoxide functions as a reducing agent due to its strong tendency to bond with oxygen, creating stable carbon dioxide. This characteristic makes it useful in metallurgy for extracting metals from their oxide ores. A prime example is its role in a blast furnace, where CO strips oxygen from iron ore (Fe2​O3​), resulting in the production of pure iron (Fe) and CO2​. Ultimately, carbon monoxide’s high affinity for oxygen underpins its capacity to reduce other compounds.

Question 8.
Write two remedies for carbon monoxide poisoning.
Answer:To treat carbon monoxide poisoning, the immediate priority is to get the affected person into fresh air. Following this, medical professionals will administer high-flow oxygen, usually through a mask. In severe cases, hyperbaric oxygen therapy might be necessary.

Question 9.
Complete the reactions and balance them.
(a) CuO + CO →
(b) Fe2O2 + CO →
Answer: