Reaction of metals with oxygen

Question 1 Why sodium and potassium are stored under kerosene oil?

Question 2 Give equation for reaction of sodium with oxygen?

Question 3 Give equation for reaction of potassium with oxygen?

Question 4 What happens when sodium oxide reacts with water?

Question 5 What happens when potassium oxide reacts with water?

Question 6 What are amphoteric oxides?

Reaction of metals with oxygen
When metals are burnt in air,they react with oxygen of air to form metal oxide.
Metal oxides are basic in nature.They turn red litmus to blue.

Sodium and potassium metal are stored under kerosene oil to prevent their reaction with the oxygen,moisture and carbon dioxide of air.They are so reactive that they react vigorously with oxygen.They catch fire and start burning when kept open in the air.

4Na(s) + O2 (g) —>2 Na2O (s)

4K(s) + + O2 (g) —>2 K20 (s)
Most of the metal oxides are insoluble in water except sodium oxide and potassium oxide.

Na2O (s) + H20 (l) —> 2NaOH (aq)

K20 (s) + + H20 (l) —–>2 KOH(aq)

2 Mg(s) + O2 (g) —–> 2MgO(s)

4Al(s) + 3 O2 (g) —-> 2 Al2O3 (s)

There are certain metal oxides which are basic as well as acidic.Those metal oxides which show acidic and basic behaviour are called as amphoteric oxides.

For Ex:Al and Zn metal form Al2O3  and ZnO..They are amphoteric in nature.

Al2O3 (s) +6 HCl —->2 AlCl3 (aq) +3 H20 (l)

Basic oxide

Al2O3 (s) + 2NaOH —–> 2 Na2ZnO2 + H20 (l)

Acidic oxide

ZnO(s) + 2HCl (aq) —–> ZnCl2  (aq) + H20 (l)

Basic oxide

ZnO(s) + 2NaOH (aq) —-> Na2ZnO2  (aq) + H20 (l)

Acidic oxide

3Fe(s) + O2 (g)—–> Fe2O3 (s)

2Cu(s) + + O2 (g) —–> 2CuO(s)

Gold and silver do not react with oxygen even at high temperature.

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