Carbon And Its Compounds II SS1 Chemistry Lesson Note

AMORPHOUS CARBON

Carbon also occurs in several other forms which have no definite crystalline structure. These non-crystalline structures which are not considered to be true allotropes include:

CHARCOAL: This is made by burning wood, bones, sugar etc in a limited amount of air. Charcoal is used to remove colour from substances. Wood charcoal is used in absorbing poisonous gases while animal charcoal is used in absorbing colours.

CARBON BLACK AND LAMP BLACK: Lamp black is obtained by burning the wick of an oil lamp excessively so that it leaves a deposit of soot on the lamp-glass and cover; while carbon black is obtained from burning coal gas, natural gas or petroleum. Carbon black and lamp black are used as an additive to rubber tyres. They are also used in making printer ink, carbon paper, black shoe polish, typewriting ribbons e.t.c

PHYSICAL PROPERTIES OF CARBON

(1) All the different allotropes of carbon are black or greyish-black solids except diamond and they are odourless and tasteless.

(2) They have a high melting point of about 35000C.

(3) They are insoluble in all common solvents like water, alkalis, acids, petrol and carbon (iv) sulphide (CS2). This is the reason carbon deposits inside motor engines have to be removed mechanically. This is known as the decarbonisation of motor engines.

CHEMICAL PROPERTIES OF CARBON

(1) Combustion:

(a) All forms of carbon burn in excess oxygen to produce carbon (iv) oxide gas.

1. C(s) + O2(g) > CO2(g)          (Complete combustion)

(b) All forms of carbon also burn in a limited supply of air to produce carbon (ii) oxide.

1. C(s) + O2(g) > CO(g)               (Incomplete combustion)

(2) Combination reaction: Carbon combines directly with certain elements such as Sulphur, Hydrogen, Calcium and Aluminium at very high temperatures.

iii. C(s) + 2S(s) > CS2(l)

Carbon (iv) sulphide

1. C(s) + 2H2(g) > CH4(g)

Methane

1. 2C(s) + Ca(s) > CaC2(s)

Calcium carbide

1. 3C(s) + 4Al(s) > Al4C3(s)

Aluminium carbide.

(3) As a reducing agent: Carbon is a strong reducing agent. It reduces the oxides of the less active metals to the metals, while carbon is itself oxidized to either carbon (iv) oxide or carbon (ii) oxide, depending on the reaction conditions.

vii. Fe2O3(s) + 3C(s) > 2Fe(s) +3CO(g)

viii. 2CuO(s) + C(s) > 2Cu(s) +CO2(gix. H2O(g) + C(s) > CO(g) + H2(g)

1. CO2(g) + C(s) > 2CO(g)

K        Na    Ca    Mg    Al    Zn    Fe    Sn    Pb    H

Cu Hg    Ag    Au

The oxide is not reduced. The oxide is reduced to the metal when heated 

ZnO(s) +)

 C(s) > Zn(s) + CO(g)

PbO(s) + C(s) > Pb(s) + CO(g)

(4) Reaction with strong oxidizing agents: When carbon is heated with conc. HNO3 or conc. H2SO4 is oxidized to Carbon (iv) oxide.

C(s) + 4HNO3(aq) > 2H2O(l) + 4NO2(g) + CO2(g)

C(s) + 2H2SO4(aq) > 2H2O(l) + 2SO2(g) + CO2(g)

ASSIGNMENT 

1. Mention the respective properties of the following allotropes of carbon that account for their uses as indicated 

(a) Diamond used for drilling rock 

(b) Diamond used as a jewel 

(c) Graphite used for slowing down neutrons in nuclear reactors. 

(d) Graphite used as electrode

2. (a) State one piece of evidence that shows that both graphite and diamond are allotropes. (b) Give reasons why graphite is soft and diamond, its allotrope is hard.