Carbon : An Important Element

A. A carbon atom forms a covalent bond with other atoms. In this bond the two atoms share electrons.

Explanation: A carbon atom forms a covalent bond with other atoms

because its outer shell is half full as shown in the figure below:

In the covalent bond, sharing of electrons takes place. For example:

CH₄

B. All the carbon bonds in a saturated hydrocarbon share electrons.

Explanation: The hydrocarbons having only single bonds between carbon atoms are called saturated hydrocarbons. Saturated

form covalent bond (by sharing of electrons)

C. At least one carbon bond in an unsaturated hydrocarbon is

double.

Explanation: Some hydrocarbons have a multiple bond between two carbon atoms. A multiple bond can be a double bond or a triple

bond. Hydrocarbons having at least one multiple bond are called unsaturated hydrocarbons.

For example, ethene

D. Carbon is the essential element in all the organic compounds.

Explanation: A carbon atom exhibits a characteristic property. It can form a chain of carbon atoms by forming covalent bonds with

other carbon atoms. Hence, it is the most essential element in the organic compounds.

E. The element hydrogen is present in most organic compounds.

Explanation: Along with carbon, the element hydrogen is also included in most organic compounds.

A. Carbon and its compounds used as fuels due to the following reasons:

1. When most of the carbon and its compounds is burnt in air, it gives a lot of heat, light and energy.

2. They have high calorific value. Thus, on burning in air, they give large amount of heat and energy.

3. When saturated hydrocarbon (hydrocarbon having single bond) is burnt in air, less smoke with a clean flame is produced.

Note: Calorific value is the amount of heat liberated in calories by the complete combustion of a combustible material with oxygen.

Carbon occurs in crystalline forms, non-crystalline(amorphous) forms and in hydrocarbons forms.

1. Carbon has three crystalline forms(allotropes) which are Diamond, Graphite and Fullerene.

2. Coal, charcoal, coke are the non-crystalline forms of carbon.

3. The two types of hydrocarbons forms in which carbon occur are saturated hydrocarbons and unsaturated hydrocarbons.

Diamond is a crystalline form of carbon. Uses of diamond are the

following:

1. Diamonds are used in making ornaments.

2. Diamonds are used in rock drilling and glass cutting machines.

3. To carry out eye surgery, diamond knives are used.

4. Diamond dust is used for polishing other diamonds.

5. Diamond is used to make windows giving protection from radiation in space and in artificial satellites.

A. Difference between diamond and graphite:

B. Difference between crystalline and non-crystalline forms of carbon:

A. Graphite is a good conductor of electricity due to the following reasons:

1. In graphite, carbon atoms are arranged in different layers.

2. In each layer, every carbon atom is linked to three neighboring carbon atoms.

3. Thus, the fourth electron of each carbon atom is free to move continuously within the entire layer.

4. Because of the presence of these free electrons in different layers, graphite becomes a god conductor of electricity.

B. Graphite is not used in ornaments due to the following facts:

1. For making ornaments, properties like transparency of substance, reflection of light and hardness should be present.

2. But in graphite, all these properties are absent.

3. It is soft, brittle, black and slippery in nature.

4. Thus, it is not used in making ornaments.

C. When limewater (CaOH)₂ is passed through CO₂, the following reaction takes place:

(CaOH)₂ + CO₂→ CaCO₃ + H₂O

Limewater Calcium

Carbonate

1. In this reaction, when limewater comes in contact with the gas released in the form of an effervescence, it turns milky. This is chemical test for carbon dioxide gas.

2. When limewater turns milky, it is confirmed that the effervescence is of carbon dioxide.

D. Biogas is an ecofriendly fuel:

a. Animal dung, dry leaves, wet garbage get decomposed by anaerobic microbes in a biogas plant.

b. This produces biogas (methane gas).

c. Biogas is a very cheap fuel option which is also used for cooking gas.

d. It is also used for production of an electricity.

e. Biogas contains about 55% to 60% methane and the rest is carbon dioxide.

f. Biogas is a very good manure and is convenient to use.

g. It is a very good manure.

A. Diamond, graphite and fullerene are the three crystalline forms of carbon.

1. A crystalline form has a definite and regular geometric pattern.

2. The structure of all the three crystalline forms has a definite shape, sharp edges and plane surfaces.

Graphite Diamond Fullerene

3. Graphite has a hexagonal layered structure.

4. Diamond has a tetragonal three-dimensional structure.

5. Fullerene exists in the form of buckyballs and buckytubes.

Petrol, diesel, coal are fossil fuels because:

1. They are main source of heat and energy.

2. They release heat, light and energy when burnt in air.

3. They are formed from the decayed living organisms (plants and animals) that are present in the earth’s crust.

Uses of various allotropes of carbon:

1. Diamond- It is used in making ornaments, rock drilling and glass cutting, artificial satellites etc.

2. Graphite- It is used in pencils, paints, polish, for making carbon electrodes, lubricants etc.

3. Fullerene- It is used as insulators, used as a catalyst in the water purification.

4. Coal- Coal is used in thermal power plants, used as fuel in factories and industries.

5. Coke- It is used as a reducing agent and a domestic fuel.

Note: Allotropes- Some elements occur in nature in more than one form. This property of elements is called allotropy. The elements which show this property are called allotropes.

CO₂ is used in fire extinguisher:

1. CO₂ is filled under pressure in the fire extinguisher.

2. When we decrease that pressure, it becomes gaseous and comes out forcefully.

3. The carbon dioxide displaces the oxygen (a main cause of fire to burn)

4. By removing oxygen, we can put out a fire.

5. The reaction taking place:

Practical uses of CO₂:

1. The most important use of CO₂ is that plants use CO₂ in the process of photosynthesis.

2. Liquid CO₂ is used as solvent in dry cleaning.

3. CO₂ is used to make aerated drinks.

4. CO₂ is used in fire extinguisher to remove oxygen.

5. Solid CO₂ is used to keep milk and milk products cool while travelling.

A. Two physical properties of diamond are:

1. Diamond is the hardest natural substance found in the earth and does not dissolve in any solvent.

2. Diamond does not show any change when treated with acids/bases.

B. Two physical properties of Charcoal are:

1. Charcoal when burnt produces bad heat and energy. It is also a bad conductor of electricity.

2. It is highly porous substance and has low density.

C. Two physical properties of Fullerene are:

1. Fullerenes dissolve in solvents like carbon disulphide (CS₂) and chlorobenzene.

2. One molecule of fullerene contains around 30 to 900 carbon atom.

1. CH₄ + 2O₂→ CO₂ + 2H₂O + heat

Explanation:

When methane (CH₄) is burnt in the presence of oxygen to form evolve a bluish flame. In the above reaction, the methane burns completely.

2. CH₄ + Cl₂→ CH₃Cl + HCl

Explanation:

Methane(CH₄) and chlorine(Cl₂) gases react with each other in presence of UV light and form mainly methyl chloride (chloromethane – CH₃Cl) and hydrogen chloride. This reaction is called chlorination of methane.

3. 2NaOH + CO₂→ Na₂CO₃ + H₂O

Explanation: When aqueous solution of sodium hydroxide is passed through carbon dioxide, it forms sodium carbonate (Na₂CO₃)

A. The different types of coal are peat, bituminous, anthracite and Lignite.

Peat- It is generally used as a fertilizer, as a packing material (due to its spongy nature).

Lignite- It is used in power generation (to generate electricity) and is used to create fertilizer products like anhydrous ammonia and ammonium sulphate.

Bituminous- It is mainly used for the combustion for coke, tar, coal, chemical and coke-oven gas. It is widely used for steam raising.

Anthracite- It is mostly used in metallurgical process and used in hand-fire furnaces.

Steps to prove that graphite conducts electricity:

Step 1: Take a pencil and sharp it from both sides.

Step 2: Now, take two clips and join each with their respective leads of the pencil.

Step 3: Also join a small bulb in the setup and connect it with a battery cell.

Step 4: Assemble the apparatus properly as shown in thee figure below.

Step 5: Start the electric current in the circuit.

Observations: You will observe that the bulb starts to glow as soon as the current is applied. This proves that graphite is good conductor of electricity.

The properties of carbon are the following:

Carbon exists in two allotropic forms which are crystalline forms and another is non-crystalline forms.

In saturated hydrocarbons (having single bond), carbon can be classified into primary carbon, secondary carbon, tertiary carbon and quarternary carbon.

Methods to verify the properties of carbon dioxide are:

1. By using limewater

Step 1: Take some limewater in a test tube.

Step 2: Take some baking soda in another test tube and add lemon juice to it. Fit the bent tube over it.

Step 3: Insert its other end into the lime water.

Observations: We will observe that limewater turns milky as it comes in contact with the released gas in the form of effervescence. When limewater turns milky, it is confirmed that the effervescence released is of carbon dioxide gas.

The reaction taking place:

Ca(OH)₂ + CO₂→ CaCO₃ + H₂O

2. Sodium carbonate is formed when carbon dioxide is passed through an aqueous solution of sodium hydroxide.

The reaction taking place:

2NaOH + CO₂→ Na₂CO₃ + H₂O

3. Sodium bicarbonate is formed on passing CO₂ through an aqueous solution of sodium carbonate.

The reaction taking place:

Na₂CO₃ + H₂O + CO₂→ 2NaHCO₃