Carbon & Its Compounds

In combined state, carbon occurs as:

1. coal
2. diamond
3. graphite
4. petroleum

Answer

petroleum

Reason — In combined state, carbon occurs in natural gas and petroleum.
Diamond is pure carbon. Graphite is pure carbon. Coal contains carbon mixed with impurities.

A crystalline form of carbon is:

1. lamp black
2. gas carbon
3. sugar
4. fullerene

Answer

fullerene

Reason — Fullerene is a crystalline form of carbon.
Lamp black is amorphous carbon. Gas carbon is amorphous carbon. Sugar is not an elemental form of carbon.

Graphite is used to make crucibles because it is:

1. a good conductor of electricity
2. a good conductor of heat
3. soft and slippery
4. has high melting point

Answer

has high melting point

Reason — Graphite is used to make crucibles because it has a high melting point.

Diamond is used for:

1. making the electrodes of electric furnaces.
2. making crucibles for melting metals.
3. cutting and drilling rocks and glass.
4. making carbon brushes for electric motors.

Answer

cutting and drilling rocks and glass.

Reason — Diamond is used for cutting and drilling rocks and glass as it is very hard.
Graphite is used in making the electrodes of electric furnaces, crucibles for melting metals, carbon brushes for electric motors.

Carbon forms innumerable compounds because:

P. it has four electrons in its outermost shell.

Q. it behaves as a metal as well as a non-metal.

R. carbon atoms can form long chains.

1. Only P is correct.
2. Only Q is correct.
3. Both P and R are correct.
4. Both Q and R are correct.

Answer

Both P and R are correct.

Reason — Carbon forms innumerable compounds because carbon atoms have the unique property of linking with one another to form very long chains of different sizes which may be straight, branched or cyclic. This property is called catenation. Carbon has four electrons in its outermost shell.

Fill in the blanks:

(a) ............... is present in both living and non-living things.

(b) The property of an element to exist in two or more forms but in the same physical state is called ............... .

(c) ............... and ............... are the two major crystalline allotropes of carbon.

(d) ............... is the hardest substance that occurs naturally.

(e) The name 'carbon' is derived from the Latin word ............... .

Answer

(a) Carbon

(b) Allotropy

(c) Graphite, Diamond

(d) Diamond

(e) Carbo

Write 'true' or 'false' against the following statements and correct the false ones :

(a) Carbon occurs as carbon dioxide in the atmosphere.

(b) Graphite is the purest form of carbon.

(c) Coloured diamonds are costlier than colourless and transparent diamonds.

(d) Graphite has layers of hexagonal carbon bondings.

(e) Diamond is soluble in all solvents.

Answer

(a) True

(b) False
Correct statement — Diamond is the purest form of carbon.

(c) False
Correct statement — Colourless and transparent diamonds are costlier than coloured diamonds.

(d) True

(e) False
Correct statement — Diamond is insoluble in all solvents.

Give an appropriate term for the following:

(a) Substances whose atoms or molecules are arranged in a definite pattern.

(b) Different forms of an element found in the same physical state.

(c) The property by which atoms of an element link together to form long chain or ring compounds.

Answer

(a) Crystals

(b) Allotropy

(c) Catenation

Name the following.

(a) The hardest naturally occurring substance.

(b) A greyish black non-metal that is a good conductor of electricity.

(c) The third crystalline form of carbon.

Answer

(a) Diamond

(b) Graphite

(c) Fullerene

How many carbon atoms are there in a Buckminster fullerene ?

Answer

60 carbon atoms are there in Buckminster fullerene.

Define the following terms:

(a) Allotropy

(b) Carat

(c) Crystal

(d) Catenation

Answer

(a) Allotropy is defined as the phenomenon due to which an element exists in two or more forms in the same physical state with identical chemical properties but with different physical properties.

(b) The weight of a diamond is expressed in terms of carats, where 1 carat = 0.2 g.

(c) A crystal is a homogeneous solid in which particles are arranged in a definite pattern due to which they have a definite geometrical shape with a plane surface.

(d) Carbon atoms possess a unique property to link themselves together to form very long chains of different sizes which may be straight, branched or cyclic and this property is called catenation.

Answer the following in brief :

(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 fullerene.

(d) What impurity is present in black diamond?

Answer

(a) In graphite, one valence electron of each carbon atom remains free, so it is a good conductor of electricity. But in diamond there are no free or mobile electrons so it does not conduct electricity.

(b) In diamond, a carbon atom has four valence electrons. Each carbon atom is linked with four neighbouring carbon atoms forming a rigid tetrahedral structure. Due to this strong bonding diamond is very hard.

(c) Fullerenes are the third crystalline allotrope of carbon. In fullerenes, many carbon atoms are held together in a cage-like structure. The most common fullerene is buckminster fullerene or buckyball.

(d) Black diamonds have copper oxide present in them as an impurity.

Give two uses of the following mentioning the property being utilized in the said use.

(a) graphite

(b) diamond

Answer

(a) The two uses of graphite are:

1. Used for making the electrodes of electric furnaces, since graphite is a good conductor of electricity.
2. Used for making crucibles for melting metals due to its high melting point.

(b) The two uses of diamond are:

1. For making jewellery because of its brilliant shine, pure diamond is used in jewellery as a gem.
2. Impure diamond (black diamond) is used for cutting and drilling rocks, glass or other diamonds due to its hard nature.

Write three differences between graphite and diamond.

Answer

Anthracite is :

1. an inferior type of coal
2. a superior type of coal
3. a cheapest form of coal
4. none of the above

Answer

a superior type of coal

Reason — Anthracite is the purest variety of coal. Its carbon content is between 92-98%.

Destructive distillation of coal yields

1. coal tar
2. coal gas
3. coke
4. all of the above

Answer

All of the above

Reason — Destructive distillation of coal produces coke, coal tar, coal gas and ammoniacal solution.

Lamp black is :

1. an amorphous form of carbon
2. a crystalline form of carbon
3. a pure form of carbon
4. a cluster of carbon atoms

Answer

an amorphous form of carbon

Reason — Lamp black is an amorphous form of carbon which contains 98-99% carbon. Lamp black is a form of carbon that does not have a regular crystal structure rest all have specific structure.

The process by which decayed plants slowly convert into coal is called

1. petrification
2. carbonization
3. carbonification
4. fermentation

Answer

carbonization

Reason — The process by which decayed plants slowly convert into coal is called carbonization.
Petrification means turning into stone (fossilization), not specifically forming coal. Fermentation is a biological process involving microorganisms (like making alcohol), not coal formation.

The purest form of the amorphous carbon is :

1. wood charcoal
2. sugar charcoal
3. bone charcoal
4. lamp black

Answer

sugar charcoal

Reason — The purest form of amorphous carbon is sugar charcoal.
Wood charcoal contains impurities like ash and volatile substances, so not very pure. Bone charcoal contains calcium phosphate and other impurities. Lamp black contains impurities.

Fill in the blanks:

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

(b) Coal is a ............... form of carbon.

(c) ............... is the most inferior form of coal.

(d) Wood charcoal is a ............... conductor of heat and electricity.

(e) ............... is used in making black shoe polish.

Answer

(a) Carbon monoxide

(b) amorphous

(c) Peat

(d) bad

(e) Lamp black (soot)

Write 'True' or 'False' against the following statements and correct the false ones.

(a) Lamp black is used in making shoe polish.

(b) Coke is obtained by destructive distillation of sugar.

(c) Activated charcoal is a good conductor of electricity.

(d) Wood charcoal is an important constituent of gun powder.

(e) Coal gas is used in the preparation of artificial fertilizers.

Answer

(a) True

(b) False
Correct statement— Coke is obtained by destructive distillation of coal.

(c) False
Correct statement — Activated charcoal is a bad conductor of electricity.

(d) True

(e) False
Correct statement — Ammoniacal solution is used in the preparation of artificial fertilizers.

Match the following:

Answer

Name the following:

(a) Substances whose atoms or molecules are not arranged in a geometrical pattern.

(b) The best variety of coal.

(c) The purest form of amorphous carbon.

(d) An amorphous form of carbon that burns without smoke.

(e) Mixture of carbon monoxide and hydrogen.

Answer

(a) Amorphous substances

(b) Anthracite

(c) Sugar charcoal

(d) Coke

(e) Water gas

Define the following:

(a) Carbonization

(b) Adsorption

(c) Destructive Distillation

Answer

(a) The process of slow conversion of vegetable matter into carbon-rich substances is called carbonization.

(b) Adsorption is the property due to which a substance adsorbs gases, liquids and solids only on its surface.

(c) When a substance is heated in the absence of air, the process is called destructive distillation. It results in the decomposition of the substance into its constituent substances.

Why is wood charcoal used in water filters and gas masks?

Answer

Wood charcoal has high adsorbing capacity, so it is used in water filters to remove impurities and in gas masks to adsorb harmful gases.

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

(a) Wood charcoal, wood tar, wood gas, pyroligneous acid.

(b) Bone charcoal, bone oil, pyridine.

(c) Carbon dioxide

(d) Artificial diamonds.

Give two uses for each of the following:

(a) coal

(b) coke

(c) wood charcoal

(d) sugar charcoal

(e) bone charcoal

(f) lamp black

Answer

(a) Coal

1. It is used both as a domestic and industrial fuel.
2. It is used to prepare coke, coal gas and coal tar.

(b) Coke

1. It is used in the manufacture of water gas (CO + H₂), producer gas (CO + N₂) and artificial graphite.
2. It is used as a smokeless industrial and domestic fuel.

(c) Wood charcoal

1. It is an important constituent of gun powder.
2. Due to its high adsorbing capacity, it is used in military and industrial gas masks to adsorb harmful gases and in water purifier filters.

(d) Sugar charcoal

1. It is used to prepare artificial diamonds.
2. It is used mostly as a reducing agent to extract metals from their respective oxides.

(e) Bone charcoal

1. It is used to decolourise cane sugar in the process of manufacturing sugar.
2. It is used to remove excess of fluoride from water which causes tooth decay.

(f) Lamp black

1. It is used in making black shoe polish, carbon paper, printing ink, black paint etc.
2. It is used in manufacture of tyres and gun powder.

What is destructive distillation? What are the products formed due to the destructive distillation of coal?

Answer

When a substance is heated in the absence of air, the process is called destructive distillation. It results in the decomposition of the substance into its constituent substances. Destructive distillation of coal produces coke, coal tar, coal gas and ammoniacal solution.

How is wood charcoal made locally? What other substances are formed in the process?

Answer

Locally, wood charcoal is prepared by the following steps:

1. Logs of wood are piled one above the other with a gap in the centre of the pile.
2. The pile is covered with wet clay to prevent the entry of air.
3. A few holes are left at the bottom of the pile.
4. The wood is set on fire.
5. When the fire dies out a greyish-black, brittle, porous solid is left behind which is wood charcoal.

The other substances formed are wood tar, wood gas and pyroligneous acid.

Describe briefly about the formation of coal.

Answer

The process of formation of coal is described below:

1. Coal was formed by the bacterial decomposition of ancient vegetable matter buried under successive layers of the earth.
2. Under the action of high pressure and temperature, in the absence of air, the decayed vegetable matter was converted into coal through a series of steps as shown in the figure below.
3. With each successive layer of coal formed, the amount of carbon present in the deposit increased and the level of impurities decreased.
4. This process of formation of coal is known as carbonization which took millions of years.

Name four types of coal with the percentage of carbon present in each.

Answer

The four types of coal are:

1. Peat — It contains about 50 to 60% carbon.
2. Lignite — It contains more than 60% carbon.
3. Bituminous — There are high, medium and low varieties of bituminous coal with carbon content 90%, 80% and 70-75% respectively.
4. Anthracite — It contains 92-98% carbon content.

The gas which keeps our earth warm is:

1. O₂
2. N₂
3. CO₂
4. Ne

Answer

CO₂

Reason — CO₂ is a greenhouse gas. It traps some of the heat coming from Earth and helps keep our planet warm.
O₂ is needed for respiration, but does not trap heat significantly. N₂ is a major component of air, but does not contribute to warming. Ne is an inert gas but has no role in warming.

The acid used in the laboratory preparation of carbon dioxide gas is:

1. dil. hydrochloric acid
2. conc. sulphuric acid
3. dil. sulphuric acid
4. conc. hydrochloric acid

Answer

dil. hydrochloric acid

Reason — The acid used in the laboratory preparation of carbon dioxide gas is dil. hydrochloric acid.
Conc. sulphuric acid forms a coating of calcium sulphate on the marble chips, stopping the reaction. Dil. sulphuric acid forms calcium sulphate (insoluble), which slows/stops the reaction. Conc. hydrochloric acid is too strong and not typically used in lab preparation; dilute acid is preferred for controlled reaction.

The metal which burns in carbon dioxide is:

1. Iron
2. Magnesium
3. Aluminium
4. Copper

Answer

Magnesium

Reason — Magnesium metal burns in the presence of carbon dioxide to give magnesium oxide and carbon (black).
Iron does not burn in carbon dioxide because it is not reactive enough to take oxygen from CO₂. Aluminium does not burn in carbon dioxide because it is covered by a protective oxide layer (Al₂O₃). Copper is even less reactive as it cannot take oxygen from CO₂ at all.

The substance used in artificial respiration is:

1. carbon
2. carbon dioxide
3. carbogen
4. carbonization

Answer

carbogen

Reason — A mixture of 5% carbon dioxide and 95% oxygen, called carbogen, is used for artificial respiration.
Carbon is an element; it is not used in respiration. Carbon dioxide alone is not used because excess CO₂ can be harmful. Carbonization is the slow process by which dead plant material turns into coal.

The substance which can sublime is :

1. baking soda
2. marble
3. lime water
4. dry ice

Answer

dry ice

Reason — Dry ice is a sublimable substance, and it directly changes into gaseous carbon dioxide, from its solid state, i.e., without passing through its liquid state.
Sodium bicarbonate does not sublime; it decomposes on heating instead. Marble does not sublime; it decomposes at high temperature. Lime water is a liquid, so it cannot sublime.

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.

(d) the action of dilute hydrochloric acid on sodium carbonate.

Answer

(a) CaCO₃ $\xrightarrow{\enspace\Delta\enspace}$ CaO + CO₂ (g)

(b) NaHCO₃ + CH₃COOH ⟶ CH₃COONa + H₂O + CO₂ (g)

(c) 2NaHCO₃ + H₂SO₄ ⟶ Na₂SO₄ + 2H₂O + 2CO₂

(d) Na₂CO₃ + 2HCl ⟶ 2NaCl + H₂O + CO₂

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) vinegar is added to baking soda?

(e) a soda water bottle is opened?

Answer

(a) When a lit splinter is introduced into a jar containing carbon dioxide, it extinguishes as carbon dioxide is a non-supporter of combustion.

(b) Carbon dioxide turns moist blue litmus red. This shows that the gas is acidic in nature.

(c) When carbon dioxide is passed through lime water first in small amounts it turns lime water milky. This is due to the formation of insoluble calcium carbonate. When excess of the gas is passed through the solution milkiness disappears. This is due to the formation of soluble calcium bicarbonate.

(d) Baking soda, i.e., sodium bicarbonate reacts with vinegar (acetic acid) to form sodium acetate, water, and releases carbon dioxide gas.

(e) Carbon dioxide gas is dissolved in water under pressure to give soda water. When a soda water bottle is opened, the pressure is released and the bottled gas escapes with a brisk effervescence that adds a fizz to the drink.

Give reasons for the following:

An excess of carbon dioxide increases the temperature of the earth.

Answer

Carbon dioxide gas traps the long-wave radiations reflected by the earth and keeps our earth warm. But due to air pollution and deforestation excess carbon dioxide gas is emitted and, along with other greenhouse gases, has created a thermal blanket around the earth, trapping more heat and thus the temperature of the earth increases.

Give reasons for the following:

Soda-acid and foam-type of fire extinguishers are not used for extinguishing electrical fires.

Answer

In both soda-acid and foam-type of fire extinguishers, the solutions are prepared in water which conducts electricity. As a result, it may generate an electric shock leading to short circuit and another fire.

Give reasons for the following:

Solid carbon dioxide is used for the refrigeration of food.

Answer

Solid carbon dioxide (dry ice) serves as a coolant and a refrigerant so it is used for the refrigeration of food like fruits, vegetables, meat, etc. which otherwise perish easily.

(a) Name the chemicals required for the preparation of carbon dioxide in the laboratory.

(b) Write the balanced chemical equation for the preparation of CO₂ in the laboratory.

(c) How will you collect CO₂ gas in the laboratory?

(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?

(f) Give a chemical test for carbon dioxide.

Answer

(a) The chemicals required for the preparation of carbon dioxide in the laboratory are:

1. Marble chips (CaCO₃)
2. Dilute hydrochloric acid

(b) CaCO₃ + 2HCl ⟶ CaCl₂ + H₂O + CO₂ (g)

(c) The gas is collected by the upward displacement of air.

(d) Laboratory preparation of carbon dioxide :

(e) Dilute sulphuric acid when reacts with marble chips (CaCO₃) forms calcium sulphate. It is insoluble in water so it covers the marble chips and stops the reaction.

CaCO₃ + H₂SO₄ ⟶ CaSO₄ + H₂O + CO₂ (g)

(f) When carbon dioxide is passed through limewater, the latter turns milky and when excess of gas is passed through the solution, milkiness disappears. This test is often used to check for the presence of carbon dioxide gas.

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 and foam-type fire extinguishers?

Answer

Fire extinguishers are devices in which carbon dioxide is produced in different forms to be used as an extinguishing agent.

Liquid carbon dioxide is the substance used in the modern type of fire extinguishers.

Modern type of fire extinguisher is an improvement over the soda-acid and foam-type fire extinguishers in the following ways:

1. Soda-acid fire extinguishers cannot be used for oil fire as the solution ejected being heavier than oil sinks below oil and does not work whereas modern type of fire extinguishers can be used to put out both oil-fed fires and electrical fires.
2. Both the soda-acid and foam-type fire extinguishers solutions are prepared in water which conducts electricity. It might generate an electric shock leading to short circuit and another fire. But in modern type fire extinguishers, liquid carbon dioxide is used which does not conduct electricity. So, it can be used to put out electrical fires.

Explain the term 'greenhouse effect'. What are its benefits? How is it harmful?

Answer

The trapping of the earth's radiated energy by carbon dioxide present in the air so as to keep the earth warm is called the greenhouse effect.

Benefits of greenhouse effect are:

1. In colder regions, this principle is applied to grow plants.
2. It makes the surface of the earth warm which provides a suitable environment for survival of living organisms.

Due to deforestation and air pollution, the total amount of carbon dioxide in the air has increased. Carbon dioxide gas along with other greenhouse gases have created a thermal blanket around the earth, trapping more heat and increasing the greenhouse effect. This further warming of the earth is known as global warming, which is harmful. Global warming has serious consequences like:

1. It will cause melting of glaciers and ice in polar regions causing floods.
2. Ecological balance will get disturbed, rainfall patterns will be changed.
3. Pattern of crop cultivation will be changed.
4. Many species of plants and animals will get extinct.

State three ways by which carbon dioxide gas is added into the atmosphere.

Answer

The three ways by which carbon dioxide gas is added into the atmosphere are:

1. Combustion of fuels.
2. Respiration of human beings, animals and plants.
3. By volcanic eruptions.

What steps should be taken to balance carbon dioxide in the atmosphere?

Answer

The steps taken to balance carbon dioxide in the atmosphere are:

1. Growing more trees and plants.
2. Reducing the consumption of fossil fuels.
3. Using filters in the chimneys of factories and power houses.
4. Using smokeless sources of energy like solar energy, biogas etc.

Fill in the blanks:

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

(b) Carbon monoxide burns in air with a ............... flame to form carbon dioxide.

(c) Carbon monoxide is a product of ............... combustion.

(d) A mixture of 95% oxygen and 5% carbon dioxide is called ...............

(e) Carbon monoxide is used as a ............... in the extraction of pure metals from their corresponding ores.

Answer

(a) Carbon monoxide

(b) pale blue

(c) incomplete

(d) carbogen

(e) reducing agent

Assertion (A): Carbon can form a large number of compounds, most of which are studied under organic chemistry.

Reason (R): Carbon atoms can form long chains with each other.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Answer

Both A and R are true and R is the correct explanation of A.

Explanation — A is true as carbon Carbon forms a huge number of compounds and is studied under organic chemistry. R is true as carbon atoms can form a large number of compounds because carbon can form long chains with each other.

Therefore, Both A and R are true and R is the correct explanation of A is the correct answer.

Assertion (A): Coal is used as a fuel for domestic purposes and industries.

Reason (R): Coal is an amorphous form of carbon.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Answer

Both A and R are true but R is not the correct explanation of A.

Explanation — A is true as coal is rich in carbon and releases a large amount of heat on burning.
R is true as coal is an amorphous form of carbon, but this is not the reason why coal is used as a fuel.

Therefore, Both A and R are true but R is not the correct explanation of A is the correct option.

Assertion (A): Diamond and graphite are crystalline allotropes of carbon.

Reason (R): Both diamond and graphite are good conductors of electricity and are used as gems.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Answer

A is true but R is false.

Explanation — A is true as diamond and graphite are crystalline allotropes of carbon. R is false as diamond is a bad conductor of electricity because it has no free or mobile electrons, but it is used for making gems. Graphite is a good conductor of electricity, but it is not used for making gems.

Therefore, A is true but R is false is the correct option.

Assertion (A): The value of diamond decreases with an increase in the impurities.

Reason (R): Colourless, transparent diamonds are the costliest.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Answer

Both A and R are true and R is the correct explanation of A.

Explanation — A is true as an increase in the impurities means lesser clarity of diamonds, which reduces their value.
R is true as colourless, transparent diamonds are the costliest as they are used for making gems and various jewellery.

Therefore, Both A and R are true and R is the correct explanation of A is the correct option.

Assertion (A): Pencil leads are made up of graphite.

Reason (R): Graphite leaves a black mark on paper.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Answer

Both A and R are true and R is the correct explanation of A.

Explanation — A is true as pencil leads are made up of graphite.
R is true as graphite leaves a black mark on paper.

Therefore, Both A and R are true and R is the correct explanation of A is the correct option.

Assertion (A): Carbon dioxide is used in fire extinguishers.

Reason (R): CO₂ gas is a non supporter of combustion, which cuts off the supply of oxygen to fire.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Answer

Both A and R are true and R is the correct explanation of A.

Explanation — A is true as carbon dioxide is used in fire extinguishers.
R is true as CO₂ gas cuts off the supply of oxygen to fire, thus helping to extinguish it.

Therefore, Both A and R are true and R is the correct explanation of A is the correct option.

Assertion (A): Carbon monoxide is an extremely poisonous gas.

Reason (R): The gas is formed due to incomplete combustion of carbon.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Answer

Both A and R are true but R is not the correct explanation of A.

Explanation — A is true as carbon monoxide is an extremely poisonous gas because carbon monoxide combines with the haemoglobin present in the red blood cells of our body to form a stable compound called carboxyhaemoglobin.
R is true as this stable compound does not allow haemoglobin to absorb or carry oxygen, thus depriving our body cells of oxygen. This causes paralysis of the respiratory organs and results in death due to suffocation (asphyxiation).

Therefore, Both A and R are true but R is not the correct explanation of A is the correct option.

How is carbon monoxide gas formed? Give a balanced equation for the reaction.

Answer

Carbon monoxide gas is formed from:

1. Incomplete burning of fuels
2. Exhaust gases of automobiles.

Carbon monoxide is a product of incomplete burning or combustion of carbon and fuels.

2C + O₂ $\xrightarrow{\enspace\Delta\enspace}$ 2CO

Give one use of carbon monoxide.

Answer

Carbon monoxide is used in the extraction of metals from their ores.

Write two remedies for carbon monoxide poisoning.

Answer

The two remedies for carbon monoxide poisoning are:

1. The victim should be given artificial respiration with carbogen to restore normal breathing.
2. The victim should be immediately brought out into the open.

Complete the chemical equations and balance them.

(a) CuO + CO $\longrightarrow$

(b) Fe₂O₃ + CO $\longrightarrow$

Answer

(a) CuO + CO $\xrightarrow {\text{heat}}$ Cu + CO₂

(b) Fe₂O₃ + 3CO $\xrightarrow {\text{heat}}$ 2Fe + 3CO₂

Match the following:

Answer

Explain the poisonous nature of carbon monoxide.

Answer

1. Carbon monoxide is a highly poisonous gas. Air containing 0.5% carbon monoxide by volume if inhaled could result in death.
2. Carbon monoxide combines with haemoglobin present in RBCs of our body to form a stable compound carboxyhaemoglobin.
3. This stable compound does not allow haemoglobin to absorb or carry oxygen, thus our body cells get deprived of oxygen. This causes paralysis of respiratory organs and results in death due to suffocation.

Why is carbon monoxide called the silent killer?

Answer

It is very dangerous to sleep in a room where coal or wood is burning and its doors and windows are closed. Owing to the limited supply of air in such a room, carbon monoxide is produced. Since the gas is colourless and has a barely detectable smell, people sleeping in the room do not feel its presence and run the risk of carbon monoxide poisoning. That is why carbon monoxide is also called a silent killer.

Explain the reducing action of carbon monoxide with a suitable example.

Answer

Carbon monoxide (CO) acts as a reducing agent because it removes oxygen from metal oxides. In doing so, the metal oxide is reduced to the metal, while CO is oxidised to carbon dioxide (CO₂).

Example:

CuO + CO $\xrightarrow{\enspace\Delta\enspace}$ Cu + CO₂

Here, CuO loses oxygen (so it is reduced to Cu) and CO gains oxygen (so it is oxidised to CO₂).

Abir went to a mall with his parents on Sunday. While walking around, he noticed red devices fixed on the walls at different places. Curious, he asked his mother about them. His mother explained that those are fire extinguishers. They help to put out fires by releasing a special gas.
His father also told him that it is now mandatory to install fire extinguishers in all kinds of buildings such as offices, schools, apartments, hospitals, etc. to keep people safe.

(a) Name the gas released by fire extinguishers to put out fires.

(b) How does this gas work in putting out the fire ?

(c) Name the type of fire extinguishers used for (i) oil fire (ii) electrical fire.

(d) Why is it dangerous to use water on electrical fire ?

Answer

(a) The gas released by fire extinguishers is carbon dioxide.

(b) Carbon dioxide helps to put out fire by:

1. Cutting off oxygen supply as fire needs oxygen to burn.
2. Forming a blanket over the fire, which prevents further burning.

(c) Types of fire extinguishers used are:

(i) Oil fire: Foam fire extinguisher

(ii) Electrical fire: Carbon dioxide fire extinguisher

(d) It is dangerous to use water on an electrical fire because of the following reasons:

1. Water is a good conductor of electricity.
2. It can cause electric shock to the person using it.
3. It may also spread the fire if live current is present.