WBBSE Solutions For Class 8 School Science Chapter 4 Occurrence Of Carbon And Its Compounds In Nature Long Answer Type Questions

Chapter 4 Occurrence Of Carbon And Its Compounds In Nature Long Answer Type Questions


Question 1. Mention the similarities between diamond and graphite.

Comparison between diamond and graphite, Similarities between diamond and graphite:


Diamond Graphite
1. Has crystalline structure. 1. Has crystalline structure.
2. Chemically very less active. 2. Chemically not very active.
3. Burns at high temperatures (800°C-850°C) in 3. Burns at high temperatures (700°C) in oxygen
oxygen to produce CO2 to produce CO2.
4. Cannot absorb any gas. 4. Cannot absorb any gas.
5. Good conductor of heat 5. Good conductor of heat.


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Question 2. Mention the dissimilarities between diamond, and graphite.

Dissimilarities between diamond and graphite:


Diamond Graphite
1. Hardest natural element. 1. Soft and slippery element.
2. Colourless and transparent. 2. Blackish grey and opaque.
3. Non-conductor of electricity. 3. Good conductor of electricity.
4. Cannot put marks on the paper. 4. Can put a mark on the paper.


Question 3. Write a short note on fullerene.


Fullerene – a new allotrope of carbon was first characterized in 1985 in the laboratory by Smalley and Kroto. This is a hollow, closed cage (polyhedral) cluster of 60 or 70 carbon atoms.

Its structure is based on polyhedra formed by fusing pentagons and hexagons-which is very much similar to geodesic domes used in architecture.

Fullerene is named after American architect R. Buckminster fullerene – the inventor of the geodesic dome. It has been subjected to extensive research since its discovery and is a promising candidate for use in electronics and medicines. It can be used to produce novel enclosure compounds by trapping metal ions within the C60cage.

WBBSE Solutions For class 8 Chapter 4 Occurrence of Carbon and Its Compounds in Nature Fullerence

Question 4. Describe an experiment to show the adsorption property of charcoal.

An Experiment To Show The Adsorption Property Of Charcoal:

The adsorption property of charcoal can be easily shown by following the experiment

Apparatus and chemicals needed: A bottle with a lid, some ink (or some colored solution), some finely crushed charcoal powder, and water.

Experiment: Let us first dissolve some ink (or some colored solution) in a small volume of water taken in a bottle with a lid.

Now pour some amount of finely crushed charcoal powder in it and close the lid. Then shake the bottle well for some time and then allow it to settle. Now the solution containing the charcoal dust is filtered.

Observation: It is found that the intensity of the color of the solution after filtration has diminished considerably.

Inference: This indicates that a significant fraction of the molecules responsible for coloration has been “adsorbed” on the charcoal.

So, by filtration, when the solid charcoal powder is separated, the intensity of the color in the filtrate decreased.

Question 5. Mention the uses of different amorphous allotropes of carbon.

The Uses Of Different Amorphous Allotropes Of Carbon:

The uses of different amorphous allotropes of carbon are briefly discussed below.

  1. Coke can be used as fuel during metal extraction and as a reducing agent in a redox reaction.
  2. Coal is primarily used as fuel.

Lamp black is used as a pigment and used for making printing ink for use in the printing press. Gas carbon is used to make electrodes for batteries, arc lamps, or electrolytic cells.

Charcoal has a remarkable property of adsorption. It can adsorb impurities from water and hence can purify water. Specially prepared charcoal, known as activated charcoal, can adsorb large amounts of gas on its surface so it is used to prepare a gas mask.

Wood charcoal can be used as fuel in households and for preparing explosives for canons. Sugar charcoal is used in the laboratory as the purest form of carbon.

Bone charcoal is used for the purification of sugar and for the preparation of ivory black color (used by painters).

Question 6. Discuss briefly the consequence of the greenhouse effect.

The increasing concentration of several greenhouse gases particularly CO2 is causing the greenhouse effect (or enhanced greenhouse effect).

This will lead to Global Warming, As a direct consequence, the polar ice caps (in which more than 90% of the earth’s total drinking water is stored) will melt.

So the water level in the oceans will rise and several coastal cities (having a habitat of millions of people) will submerge. The ecosystem will be adversely affected.

Increasing temperature will enhance the growth of mosquitoes which in turn, will spread mosquito-borne diseases. Biodiversity will be hampered and several parts of the world may face drought-like conditions for a prolonged time.

In short, the effect of the greenhouse effect (or enhanced greenhouse effect) will bring devastation.

Question 7. Write a short note on biofuel.


Biofuel is a fuel that is derived from biological materials. Hydrocarbon fuel that is produced from organic matter (living or once-living material) in a short period of time (days, weeks, or even months) can be considered biofuel.

Ethanol, bio-diesel, and methanol are the three most important examples of biofuels. In India, bio-fuels are produced from oil obtained from the seeds of Jatropha plants.

The Jatropha oil can be used directly in diesel generators or diesel engines. It can also be used as a diesel additive.

Since Jatropha can be cultivated in less fertile and dry lands, its cultivation is economically beneficial from the perspective of our country.

Question 8. Write a short note on tidal energy as an alternative to fossil fuel.

Tidal energy

Tidal energy is a form of hydropower that converts the energy of tides into more usable forms of energy, such as electricity.

Tidal energy is produced by the surge of ocean waters during the rise and fall of tides. High tide and ebb always occur twice a day.

Unlike wind, tides are predictable and stable. Usually, turbines are placed in tidal streams (a fast-flowing body of water created by tides).

The kinetic energy of the tidal stream is utilized to rotate turbines which in turn produce electricity. Tidal energy is more powerful and effective than wind energy.

Since, our country has very long coastlines, this form of renewable energy can be effectively utilized as an alternative form of energy.

Question 9. Describe an experiment to show that CO2 is heavier than air.


Let us take a balloon, a rubber band, sodium bicarbonate and vinegar, and a glass bottle. First, solid sodium bicarbonate and vinegar are taken together in the glass bottle and the balloon is fixed at the mouth of the bottle.

Due to the reaction between vinegar and sodium bicarbonate, CO2 gas is produced. This gas will inflate the balloon. Now the balloon is taken out and its mouth is tied tightly with a cord, and then it is released.

It is found that the balloon is not floating. Rather it just lies on the floor. This is because CO2 is heavier than air and that is why it did not float but settled on the floor.

WBBSE Solutions For class 8 Chapter 4 Occurrence of Carbon and Its Compounds in Nature Sodium bicarbonate

Question 10. Describe an experiment to show that CO2 is soluble in water.


A Wolfe’s bottle is used to produce CO2 gas and the gas formed is passed through a gas jar filled with water.

After allowing CO2 gas to flow through the water for sufficient time, a blue litmus paper and a red litmus paper are dipped in that water.

The blue litmus paper turns red, indicating that the solution is acidic. Water becomes acidic because CO2 dissolves in water to produce carbolic acid (H2C03). H2C03 is a weak acid and it turns blue litmus paper red.

⇒ \(\mathrm{CO}_2+\mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{H}_2 \mathrm{CO}_3\)

WBBSE Solutions For class 8 Chapter 4 Occurrence of Carbon and Its Compounds in Nature Thistle funnel


The solubility of CO2 in water is increased by applying pressure. By applying pressure, CO2 is dissolved in soft drinks.

When the bottle is opened, the pressure is released, the solubility of CO2 in water decreases and bubbles of CO2 evolved from the bottle.

Question 11. Discuss briefly the oxidizing property of carbon dioxide.

Oxidizing property of CO2:

In powder or iron dust, the metals are oxidized to metal oxides, and CO2 is reduced to carbon or carbon monoxide When CO2 gas is passed over red hot carbon, C is oxidized to CO, and CO2 is reduced to CO.


WBBSE Solutions For class 8 Chapter 4 Occurrence of Carbon and Its Compounds in Nature Oxidizing property of co2


Question 12. What will happen if CO2 gas is bubbled through clear lime water? What will happen if more CO2 is passed through that same solution? What will happen if that solution is further boiled?

CO2 is an acidic oxide. It reacts with a base to form carbonate compounds. For example, some lime water is taken in a test tube and CO2 gas is bubbled through it.

Lime water turns milky due to the formation of calcium carbonate (CaCO2 ) which is insoluble and remains suspended in the solution.

\(\mathrm{Ca}(\mathrm{OH})_2+\mathrm{CO}_2 \rightarrow \mathrm{CaCO}_3+\mathrm{H}_2 \mathrm{O}\)


If more CO2 is passed through the milky water, calcium bicarbonate [CafHCOjJ is formed, which is soluble in water. So the solution becomes clear.

\(\mathrm{Ca}(\mathrm{OH})_2+\mathrm{CO}_2+\mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{Ca}\left(\mathrm{HCO}_3\right)_2\)


If the clear solution is boiled, it again turns milky, since the bicarbonate dissociates to form CaCO3 again.

\(\mathrm{Ca}\left(\mathrm{HCO}_3\right)_2 \rightarrow \mathrm{CaCO}_3+\mathrm{CO}_2+\mathrm{H}_2 \mathrm{O}\)


Question 13. Write a short note on the greenhouse effect. What do you mean by global warming?

Greenhouse Effect:

During the daytime, sunlight falls on the earth through invisible radiation, called infrared radiation, which is primarily responsible for the sensation of heat.

In the night the absorbed heat is radiated back to space by the earth’s surface.

A part of this low-energy infrared radiation is absorbed by the gases present in the atmosphere such as carbon dioxide, water vapor, methane, nitrous oxide, ozone, and some other man-made chemicals (such as chlorofluorocarbons).

This mechanism keeps the earth warm. This is known as the greenhouse effect and the gases present in the atmosphere which absorbs the radiated heat by the earth are called greenhouse gases. This is absolutely essential for the existence of living beings on earth.

Global warming is the increase in the global mean temperature consequent to the disturbance

The balance between the sun’s heat radiated towards the earth and the terrestrial heat re-radiated back to space caused by increased accumulation of greenhouse gases in the atmosphere.

Since 1975 the global temperature has undergone an increase at a rate of roughly 0.15-0.2X per decade.

Question 14. Write a short note on cellulose. What is a monomer?


Cellulose is a polymeric carbohydrate that is biodegradable. It is the main constituent of the fiber of cotton and straw.

These polymeric carbohydrates are decomposed in nature by microorganisms such as fungi and bacteria.

Cellulose-based polymers are being developed to prepare biodegradable polymers with desired chemical and mechanical properties, which are non-toxic and can be naturally decomposed.

The small repeating molecules which join together to form a polymer are called monomers. The monomers may all be of the same compound or of two different compounds.

The polymer cellulose has only one type of monomers whereas nylon has two types of monomers arranged alternatively.

Question 15. What do you mean by an alternative source of energy? On what factors does the calorific value of fuels depend?

Alternative Source Of Energy:

Those sources of energy which are not based on the burning of fossil fuels or fission of nuclear fuels and are non-polluting are called the alternative source of energy.

These are:

  1. Solar energy
  2. Hydel energy
  3. Geothermal energy
  4. Biomass energy etc.

The various factors that affect the calorific value of fuel are:

  1. A fixed percentage of carbon indicates the organic matter that does not undergo volatilization during combustion.
  2. The moisture content of the fuel
  3. Percentage of volatile matter, which expresses the organic and inorganic matter obtainable from the thermal decomposition of the fuel.

Question 16. Describe the carbon cycle through a word diagram.

Carbon Cycle through a word diagram:

WBBSE Solutions For class 8 Chapter 4 Occurrence of Carbon and Its Compounds in Nature Carbon cycle

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