PHYSICAL AND CHEMICAL PROPERTIES OF OXYGEN

SECOND TERM E-LEARNING NOTES

SUBJECT: CHEMISTRY

CLASS: SS 2

SCHEME OF WORK

WEEK 3

TOPIC: OXYGEN

CONTENTS:

1. GENERAL PROPERTIES OF OXYGEN, ELECTRONIC CONFIGURATION AND BONDING CAPACITY OF OXYGEN
2. LABORATORY AND INDUSTRIAL PREPARATION OF OXYGEN
3. PHYSICAL AND CHEMICAL PROPERTIES OF OXYGEN.
4. COMPOUNDS OF OXYGEN AND USES OF OXYGEN

PERIOD 3: PHYSICAL AND CHEMICAL PROPERTIES OF OXYGEN

PHYSICAL PROPERTIES

1. Pure oxygen is colourless, odourless and tasteless.
2. It is slightly denser than air.
3. It is slightly soluble in water.
4. It is a diatomic (O₂) gas that is neutral to litmus paper.
5. It boils (turn to gas) at -183⁰C and solidifies at -225⁰C

CHEMICAL PROPERTIES

1. Reaction with metals: Metals such as Na, K, Ca, Mg, Al, Zn burn brightly in oxygen. Metals such as silver, Gold and platinum do not react with oxygen. Oxides of metals are generally basic. e.g.

4Na_(s)+ O_2(g) 2Na₂O_(g)

1. Reaction with non-metals: Some burning non-metals when lowered into a jar of oxygen, burn to form acidic oxides or acid anhydrides which when dissolved in water form acidic solutions. E.g.

C_(s) + O_2(g) CO_2(g)

CO_2(g) + H₂O_(l) H₂CO_3(aq)

1. Test for oxygen: Oxygen is identified by its ability to rekindle a glowing splint. Nitrogen (I) oxide does this as well but is distinguished from oxygen by its pleasant sickly smell while oxygen is odourless. Oxygen also reacts with nitrogen(II)0xide to give brown fumes of nitrogen(IV)oxide which nitrogen(I)oxide does not do.

NO _(g) + O_2(g) NO_2(g)

Reaction of oxygen:

Oxidation and combustion:

Many compounds are oxidized when heated in oxygen (combustion). E.g. all hydrocarbons burn in oxygen to form carbon (iv) oxide and water, sulphides burn in oxygen to give sulphur (iv) oxides.

1. With carbon

C_(s) + O_2(g) CO_2(g)

1. With sulphur

S_(s) + O_2(g) SO_2(g)

1. With phosphorus

4P_(s) + 5O_2(g) P₄O_10(s)

1. Formation of water: Hydrogen burns violently in oxygen with a pale –blue flame, to produce water.

2H_2(g) + O_2(g) 2H₂O_(l)

1. Formation of Ozone: When a silent electric discharge is passed through oxygen, gaseous ozone, O₃, (trioxygen) is formed. The reaction is reversible:

3O₂(g) ⇌ 2O_3(g)

Ozone is an allotrope of oxygen. Allotropes are two or more different forms of the same element, in the same physical state. The phenomenon is called allotropy. Other elements that exhibits allotropy are sulphur, carbon and phosphorous.

EVALUATION

1. Write two equations for each, showing reaction of oxygen with metal and with non- metal.
2. Enumerate three physical properties of oxygen
3. List five chemical properties of oxygen.
4. Mention the allotropes of oxygen.