Science And Technology Solutions Solutions for Class 9 Science Chapter 13 - Carbon : An Important Element

Answer:

Answer:

a. Carbon and its compounds are used as fuels because most of the carbon compounds produce lot of heat and energy when burnt in air i.e. they have high calorific value.

b. Carbon occurs in the following compounds:

Hydrocarbons: These are organic compounds which are made up of carbon and hydrogen.
CO₂: Carbon also exisits as carbon dioxide and occurs in the air in free state. it is also found as a salt in chalk and limestone. It is given out during combustion of wood, fossil fuel etc.
CH₄: Carbon also exists as methane.

c. Uses of diamonds are as follows:

• used in ornaments
• used in glass cutting and rock drilling machines
• diamond dust is used for polishing other diamonds
• diamond is used to make windows giving protection from radiation in space and in artificial satellites
• diamond knives are used in eye surgery

Answer:

a. 

Answer:

a. Graphite is a good conductor of electricity because there are free electrons present between its layers. These free electrons move continuously within the entire layer and thus lead to conduction of electricity.

b. Graphite is not used in making ornaments because it is soft, britlle and slippery. It cannot be moulded like gold and silver and neither does it posess and lusture which is a desired characteritics in jewellery.

c. When carbon dioxide gas is passed through lime water, it turns milky due to the formation of calcium carbonate.

d. Biogas is an eco-friendly fuel because it helps to reduce the greenhouse gas emissions and our dependency on fossil fuels. It is produced from decomposition of organic matter, thus is an effective way of disposal of organic waste.

Answer:

a. Diamond, graphite and fullerene are crystalline forms of carbon. They are allotropes of carbon and this property of carbon is termed as allotropy. These crystalline forms of carbon have a regular and definite geometrical shape, sharp edges and plane surfaces.

b. Methane is called marsh gas because it is found at the surface of marshy places (a type of wetland, an area of land where water covers ground for long periods of time which are usually treeless and is dominated by grasses and herbaceous plants).

​c. Petrol, diesel, coal are fossil fuels because they are fuels obtained from fossils such as dead sea organisms, dead plants and animals, etc is known as fossil fuel. They are formed from the dead remains of living organisms, both aquatic and terrestrial, which have been buried for millions of years under the ground. 

d. 

• it does not conduct electricity thus making it an ideal fire suppressant for use in electrical instruments like computers etc.
• it does not create any toxic or other by-products when used to suppress a fire.

• it is used for getting special effects of a mist in dramas and movies
• it is used to make aerated drinks
• solid carbon dioxide is used in cold storage and also to keep milk and milk products and frozen substances cool during transport
• liquid CO₂ is used as solvent in modern eco-friendly dry cleaning
• CO₂ obtained by chemical reaction or kept under pressure is used in fire extinguishers
• plants use CO₂ in air for photosynthesis

Answer:

a. Physical properties of diamond:

• It is the hardest naturally occurring substance.
• Pure diamond is colourless, transparent, but brittle solid.

• It is a highly porous and brittle material 
• It is a bad conductor of heat and electricity.

• They exist in the form of buckyballs and buckytubes.
• They are made up of 60 C atoms.

Answer:

1. CH₄ + 2O₂ CO₂ + 2H₂ O + Heat
2. CH₄ + Cl₂ CH₃ Cl + HCl
3. 2 NaOH + CO₂ $\to$ Na₂CO₃ + H₂O

Answer:

a. The different types of coal are:

Peat: It is the first step of coal formation. It has high water content and less than 60% carbon content.
Lignite: Linite is a transformed form of peat and has around 25-35% of carbon content. It is a low quality brown coal with very little percentage of carbon in it. It is however used in the generation of electricity.
Bituminous: It is the most commonly found variety of coal in India is bituminous and has a carbon content of 70-90%. It is used for almost all daily requirements of coal.
Anthracite: It is the best known variety of coal found in India. It has a carbon content of more than 80% which makes it suitable for iron smelting. 

b. Graphite is a good conductor of electricity can be proved from the following experiment. 
We would require some apparatus- pencil, electrical wires, battery/cell, small bulb.

Set up the apparatus as shown in the figure.




If the bulb glows on attaching the clips to both the ends of the graphite in the pencil, it means that graphite conducts electricity. If the bulb does not glow it means that graphite does not conduct electricity.

c. Carbon has the following properties:

Physical properties:
Carbon is a soft, dull gray or black non-metal.
It exists in two forms i.e. crystalline and non crystalline forms. This property is termed as allotropy.

Chemical properties:
The chemical properties of carbon ca be explained on the basis of reactions which carbon and its compound show.

1. Combustion reaction: 

Carbon, in all its allotropic forms, burns in oxygen to give carbon dioxide along with the release of heat and light. This reaction is termed as combustion reaction.
The chemical equation to represent the burning of carbon is as follows:



2. Oxidation reaction: Pure carbon is oxidized to give carbon dioxide when burnt in air. Similarly, hydrocarbons can be easily oxidized on burning. Substances that have the ability to oxidize other substances are known as oxidizing agents. Alkaline potassium permanganate and potassium dichromate are examples of oxidizing agents. For example, the oxidation of ethanol in the presence of potassium permanganate leads to the formation of ethanoic acid.

3. Addition reaction: In an addition reaction, a substance is added to a hydrocarbon. A single product is obtained in this reaction. In unsaturated hydrocarbons, double or triple bonds are present. Atoms of different elements like hydrogen, chlorine, bromine etc. are added to these compounds across the double or triple bonds using different reagents and catalysts.

4. Substitution reaction: It is a type of reaction in which an atom or a group of atoms replaces another atom present in a molecule undergoing the reaction. For example, chlorine replaces hydrogen from methane in the presence of sunlight.

Diamond: In diamond, each atom of carbon of the given crystal unit is surrounded by four other carbon atoms, which are joined by covalent bonds, such that they form a regular tetrahedron. The diamond crystal is a compact structure in which atoms of a single unit lie in different planes. Thus, the atoms cannot slip because of their different positions in different planes and hence, diamond is the hardest naturally occurring substance.

Graphite: In graphite, atoms of a single crystal are arranged in a hexagonal ring in a single plane. The bonds between the carbon atoms of two single crystals in the parallel planes are weak. Thus, one plane can easily slide over another plane by applying pressure. This is why graphite is soft and can be used as a lubricant.

Buckminsterfullerene: It is the third and the most recently discovered allotrope of carbon. Buckminsterfullerene is a cluster of sixty carbon atoms arranged in the form of a football. It is named after the American architect Buckminster Fuller, as it resembled the geodesic dome designed by him. Since it contains sixty carbon atoms, its chemical formula is C60.

ii. Amorphous/Non-crystalline forms:

Charcoal: It is produced from the bones of animals, combustion of wood etc.

• Lignite with 25-35% of carbon content.
• Anthracite with carbon content of more than 80%.
• Bituminous coal with 60-80% carbon
• Peat with less than 60% carbon content.

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