1. Group 6 Members General comment Elements symbol Oxygen O Sulphur S
Group 6B elements show the usual gradual change from nonmetallic to metallic properties with increasing atomic number that occur in the periodic group.
Oxygen and sulphur are non metals

2. Group 6 Oxygen Oxygen Occurrence Preparation Industrial preparation
Oxygen is the most abundant element in the earth’s crust (approximately 50%). It occurs free in the atmosphere to the extent of about 21% by volume (23% by weight).
Oxygen
Preparation
Industrial preparation
By fractional distillation of air from which water vapour and carbon dioxide have been removed.

3. Group 6 Oxygen Oxygen Preparation Laboratory preparation
By catalytic (MnO2) decomposition of hydrogen peroxide.
2H2O2 (aq) → 2H2O (l) + O2 (g)
Oxygen
Chemical properties
Oxygen reacts with metals and non metals to form oxides
Examples
2H2(g) + O2(g) → 2H2O (l)
2Cu (s) + O2(g) → 2CuO (s)

4. Group 6 Water hardness Water Existence Definition
It is the most abundant liquid on earth. It exists in three states as ice, water and steam.
Preparation
Chemically, it can be prepared by reacting hydrogen and oxygen.
2H2 (g) + O2 (g) → 2H2O (l)
Water hardness
Definition
Hard water is the one that does not lather easily with soap but form insoluble scum.

5. Group 6 Water hardness Water hardness Types of hard water
Temporary hard water
It is hardness caused by calcium and magnesium hydrogen carbonates. It can be removed by boiling
Ca(HCO3)2 (aq)
→ CaCO3 (s) + 2H2O (l)
Water hardness
Types of hard water
(b) Permanent hard water
It is caused by calcium and hydrogen sulphates; it can not be removed by boiling

6. Group 6 Water hardness Water hardness
Methods of softening hard water
(a) Addition of washing soda (sodium carbonate).
The calcium and magnesium ions in water react with the carbonate ions from sodium carbonate to form insoluble carbonates.
Ca2+ (aq) + CO32- (aq) → CaCO3 (s)
Mg2+ (aq) + CO32- (aq) → MgCO3 (s)
Water hardness
Methods of softening hard water
The ion exchange process:
(b) Permutit is a cationic exchanger called sodium aluminium silicate (abbreviated here to Na+Al -silicate) which is insoluble in water. When a slow stream of hard water is passed through this material, the calcium and magnesium ions are exchanged with the sodium ions in the permutit.

7. Group 6 Water hardness Water hardness
Methods of softening hard water
(a) Addition of washing soda (sodium carbonate).
The calcium and magnesium ions in water react with the carbonate ions from sodium carbonate to form insoluble carbonates.
Ca2+ (aq) + CO32- (aq) → CaCO3 (s)
Mg2+ (aq) + CO32- (aq) → MgCO3 (s)
Water hardness
Methods of softening hard water
(b) The ion exchange process:
Permutit is a cationic exchanger called sodium aluminium silicate (abbreviated here to Na+Al -silicate) which is insoluble in water. When a slow stream of hard water is passed through this material, the calcium and magnesium ions are exchanged with the sodium ions in the permutit.

8. Group 6 Water hardness Water hardness Methods of softening hard water
(b) The ion exchange process:
Equations
Ca2+ (aq) + 2Na+Al-silicate- (s) →
Ca2+(Al-silicate-)2 (s) + 2Na+ (aq)
Mg2+ (aq) + 2Na+Al-silicate- (s) →
Mg2+(Al-silicate-)2 (s) + 2Na+ (aq)
Water hardness
Methods of softening hard water
(b) The ion exchange process:
The water now contains dissolved sodium ions that have no effect on the soap.

9. Group 6 Hydrogen peroxide, H2O2 Hydrogen peroxide, H2O2
Laboratory preparation of hydrogen peroxide
Metallic peroxides react with acids to form hydrogen peroxide, and both hydrated barium peroxide and sodium peroxide give reasonably concentrated aqueous solutions of hydrogen peroxide on treatment with ice- cold sulphuric acid:
Hydrogen peroxide, H2O2
Laboratory preparation of hydrogen peroxide
Equations
BaO2.8H2O (s) + H2SO4 (aq) →
BaSO4 (s) + H2O2 (aq) + 8H2O (l)
Na2O2 (s) + H2SO4 (aq) →
Na2SO4 (aq) + H2O2 (aq)

10. Group 6 Hydrogen peroxide, H2O2 Hydrogen peroxide, H2O2 Reactions
(a) It decomposes into water and oxygen
2H2O2 (l) → 2H2O (l) + O2 (g)
This decomposition is speeded by finely divided manganese (IV) oxide and metals.
Hydrogen peroxide, H2O2
Reactions
(b) Reaction as oxidizing agent.
Hydrogen peroxide (even in dilute solution oxidizes lead sulphide to lead sulphate, and in acidic solution, it oxidizes iron (II) salts and iodides to iron (III) salts and iodine respectively.

11. Group 6 Hydrogen peroxide, H2O2 Hydrogen peroxide, H2O2 Reactions
(b) Reaction as oxidizing agent
Equations
PbS (s) + 4H2O2 (aq) →
PbSO4 (s) + 4H2O (l)
Fe2+ (aq) + H2O2 (aq) + 2H+ (aq) →
2Fe3+ (aq) + 2H2O (l)
2I- (aq) + H2O2 (aq) + 2H+ (aq) →
I2 (aq) + 2H2O (l)
Hydrogen peroxide, H2O2
Reactions
(b) Reaction as oxidizing agent.
Hydrogen peroxide (even in dilute solution oxidizes lead sulphide to lead sulphate, and in acidic solution, it oxidizes iron (II) salts and iodides to iron (III) salts and iodine respectively.

12. Group 6 Hydrogen peroxide, H2O2 Hydrogen peroxide, H2O2 Reactions
(b) Reaction as oxidizing agent
Equations
PbS (s) + 4H2O2 (aq) →
PbSO4 (s) + 4H2O (l)
Fe2+ (aq) + H2O2 (aq) + 2H+ (aq) →
2Fe3+ (aq) + 2H2O (l)
2I- (aq) + H2O2 (aq) + 2H+ (aq) →
I2 (aq) + 2H2O (l)
Hydrogen peroxide, H2O2
Reactions
(c) Reaction as a reducing agent.
Hydrogen peroxide is oxidized by powerful oxidizing agents such as silver oxide and acidified potassium permanganate (VII) to water and oxygen:

13. Group 6 Hydrogen peroxide, H2O2 Hydrogen peroxide, H2O2 Reactions
(c) Reaction as a reducing agent.
Equations
Ag2O (s) + H2O2 (aq) →
2Ag (s) + H2O (l) + O2 (g)
2MnO4- (aq) + 5H2O2 (aq) + 6H+ (aq)
→ 2Mn2+ (aq) + 8H2O (l) + 5O2 (g)
Hydrogen peroxide, H2O2
Uses
(a) It is used, because of its oxidizing powers as:
(i) a mild bleaching agent.
(ii) As water is the only product formed, it can be used to bleach delicate materials such as silk, straw and human hair.

14. Group 6 Hydrogen peroxide, H2O2 Sulphur Uses Occurrence
(iii) It is also used in restoring old pictures
(iv) as a mild antiseptic in mouth washes and for dressing cuts and scratches
(vi) It is also used in making sodium peroxoborate (III) (used in washing powders as a source of hydrogen peroxide) and sodium chlorate (III) (used as a bleaching agent).
Sulphur
Occurrence
It occurs a sulphur, sulphides e.g. ZnS, sulphates e.g. CaSO4 or oxides e.g. SO2.

15. Group 6 Sulphur Sulphur Chemical properties Chemical properties
Sulphur forms compounds in which it exhibits a wide number of oxidation states from -2 to +6
Sulphur
Chemical properties
(a) Combines with metals when heated to give sulphides.
Mg (s) + S (s) → MgS (s)

16. Group 6 Sulphur Sulphur Chemical properties Chemical properties
(b) The principal reactions of sulphur with non-metals are summarized below: -
S (s) + 3F2 (g) → SF6 (g)
2S (s) + Cl2 (g) → S2Cl2 (g)
C (s) + 2S (s) → CS2 (l)
S (s) + O2 (g) → SO2 (g)
H2 (g) + S (l) H2S (g)
Sulphur
Chemical properties
(c) Sulphur reacts with concentrated solutions of alkalis to form a sulphide and a sulphite which reacts with more sulphur to form poly sulphides and thiosulphate respectively.
3S (s) + 6OH- (aq) →
2S2- (aq) + SO32- (aq) + 3H2O (l)

17. Group 6 Hydrogen sulphide Hydrogen sulphide
It is a bad smelling covalently bonded gas.
Hydrogen sulphide
Preparation
By reaction between metal sulphides with aqueous hydrochloric acid.
FeS (s) + 2HCl (aq) →
FeCl2 (aq) + H2S (g)

18. Group 6 Hydrogen sulphide Hydrogen sulphide Reactions Reactions
(a) It ionizes in water to give a weakly acidic solution.
  H2O (l) + H2S (g) →
H3O+ (aq) + HS- (aq)
H2O (l) + HS- (aq) →
H3O+ (aq) + S2- (aq)
Hydrogen sulphide
Reactions
(b) React with alkalis to form salts.
OH- (aq) + H2S (g)
H2O (l) + HS- (aq)
OH- (aq) + HS- (aq)
H2O (l) + S2- (aq)

19. Group 6 Hydrogen sulphide Hydrogen sulphide Reactions Reactions
(c) Hydrogen sulphide reacts with many metal ions (Hg2+, Pb2+, Sb2+, Cu2+, etc.) to form insoluble precipitates.
Pb2+ (aq) + H2S (g) →
PbS (s) + 2H+ (aq)
Hydrogen sulphide
Reactions
The formation of black precipitate of lead sulphide formed when hydrogen sulphide comes in contact with a filter paper strip dipped in lead ethanoate solution is a convenient test for the gas.

20. Group 6 Hydrogen sulphide Reactions
(d) Hydrogen sulphide burns readily in air, being oxidized to sulphur or sulphur dioxide, depending on the amount of oxygen.
2H2S (g) + 3O2 (g) →
2H2O (g) + 2SO2 (g) (a)
2H2S (g) + O2 (g)
→ 2H2O (g) + 2S (s) ……... (b)
Hydrogen sulphide
Reactions
Reaction of hydrogen sulphide with oxygen to form sulphur explain the formation of a clouds solution when saturated solution of hydrogen sulphide is left standing for some time
2H2S (g) + O2 (g)
→ 2H2O (g) + 2S (s)

21. Group 6 Hydrogen sulphide Hydrogen sulphide Reactions
(e) It can also be oxidized by many oxidizing agents such as moist chlorine, moist sulphur dioxide, iron (III) ions, acidified dichromate (VI) and manganate (VII) solution to sulphur.
Hydrogen sulphide
Equations
(Moist) Cl2 (g) + H2S (g)
→ 2HCl (g) + S (s)
(Moist) SO2 (g) + 2H2S (g)
→ 2H2O (l) + 3S (s)
H2SO4 (l) + H2S (g)
→ SO2 (g) + 2H2O (l) + S (s)
2Fe3+ (aq) + H2S (g)
→ 2Fe2+ (aq) + 2H+ (aq) + S (s)