HYDROGEN PEROXIDE

   HYDROGEN PEROXIDE  ( H₂O₂)

      H₂O₂ is the oxide of hydrogen.

Laboratory Preparation

H₂O₂ is prepared by the action of a cold dilute acid on a certain metallic peroxide e.g. BaO₂, Na₂O₂.

BaO_2(s) + H₂SO_4(aq)                  BaSO_4(s) + H₂O_2(l)

Na₂O₂+  H₂SO_4(aq)                      Na₂SO_4(aq) + H₂O_2(aq)

Industrial Preparation of Hydrogen Peroxides by the oxidation of prapan-2-ol with oxygen under slight pressure.

(CH₃)₂ CHOH + O_2(g)                                       (CH₃)₂ C = O_(l) + H₂O_2(l)

Physical Properties

• Pale-blue liquid (pure)
• It freezes to a white crystalline solid at -0.9⁰C
• It boils with decomposition at 150⁰C
• Dissolves in water to give a very weak acidic solution.

Chemical Properties

1. On warming H₂O₂ give out oxygen.

2H₂O_2(l)                                       2H₂O + O_2(l)

• H₂O₂ decomposes on exposure to air to form water and oxygen

2H₂O_2(l)                                       2H₂O_(l) + O_2(l)

• As an oxidizing agent.

H₂O₂ oxidizes lead(ii)sulphide PbS to lead(ii)tetraoxosulphate(vi)

PbS_(s) + H₂O_2(aq)                                          PbSO_4(s) + 4H₂O_(l)

– It reacts with acidified solution of potassium iodide to liberate free iodine

2KI + H₂SO₂ + H₂O_2(aq)                              K₂SO_4(s) +I_2(s) + 2H₂O_(l)

• H₂O₂ as a reducing agent

PbO₂ +2H₂O_(l) PbO + 2H₂O_2(l) + 2O₂

Ag2O + H₂O_2(l)                                          2Ag + H₂O_(l) + O_2(g)

Uses of Hydrogen Peroxide

1. H₂O₂ is used in bleaching of textile and wood pulp for paper making.
2. It is used for water purification.
3. It is used in the oxidation of dyestuffs in photography.
4. It is used in production of porous concrete and foam in rubber.
5. It is a useful antiseptic for the cleaning of the mouth and wounds.
6. It is used in rockets and sub-marines.

Ozone

Ozone is an allotropic form of oxygen. It is usually prepared  from oxygen by using silent electric discharge. Energy is introduced to oxygen at low temperature to prevent the unstable ozone from decomposing as soon as  it is formed. The apparatus consist of two conctric glass tubes lined with thin foil and arranged such that oxygen can pass through the space between them. The two terminals of an induction coil are connected to the tin foil on the two tubes respectively. The liberated gas is a mixture of ozone and oxygen called ozonised oxygen. The mixed ozone is liquefied to obtain nearly pure ozone. Oxygen boils off at -183⁰C leaving ozone, which boils at -112⁰C

Properties (Physical)

1. It is a pale-blue gas, the liquid is obtained by liquefaction and it is deep/dark blue in colour.
2. At low concentrations, the odour of ozone is pleasant, but at higher concentrations the odour is strong and unpleasant.
3. It is extremely poisonous.
4. The boiling point of ozone is -112⁰C 

Chemical Properties

It is a strong oxidizing agent oxidizes hydrogen sulphide to tetraoxosulphate(vi)acid, H₂SO₄.

H₂S +  4O_3(g)                    H₂SO_4(aq) + 4O_2(g)

PbS + 4O_3(g)                      PbSO₄ + 4O_2(g)

SO_2(g) + O_3(g)                    SO_3(g) + O_2(g)

Oxygen is more powerful oxidizing agent than oxygen, ozone decomposes to ordinary oxygen (O₂) when heated or just allowed to stand.

2O₃             ^heat    3O_2(g)

             Test for Ozone

• It has an odour similar to that of diluted chlorine.
• It oxidizes mercury and leaves a trial of mercury stuck to the glass as the mercury flow across it.

  Uses of Ozone

1. It is used to eliminate bad odour.
   1. It is used as a disinfectant to remove the undesirable odour and taste in water by killing the harmful bacteria.
   1. Ozone is used in bleaching.

EVALUATION:  How is hydrogen peroxide produced in the laboratory

ASSIGNMENT: Name two common air pollutants and give one source for each pollutant

named.

                        State one air pollutant generated during the manufacture of fertilizers

                        Give two properties to distinguish oxygen from ozone.