Discuss some chemical properties of metals.

Solution

(a) Reaction with Air:

(i) Metals are converted into their oxides by the action of oxygen present in air.

4Na     + O2   2Na2O

Sodium      Oxygen Sodium oxide

(ii) Some metals are not affected by dry air. Zinc and aluminium are oxidized by moist air only to form their oxides.

2Zn      + O2      2ZnO

Zinc    Moist air    Zinc oxide

(iii) Some metals like magnesium and calcium form oxides when heated in air.

2Mg     + O2 2MgO (Magnesium oxide)

2Ca     + O2   2CaO (Calcium oxide)

Water solutions of metal oxides are basic and turn red litmus blue.

(b) Reaction with Hydrogen: Active metals like Na, K, Ca, Mg etc. react with hydrogen to form their hydrides when heated at a temperature of 400°C and 200 atmospheric pressure.

2Na    + H2 2NaH

Sodium (Sodium hydride)

Ca     + H2 CaH2

Calcium (Calcium hydride)

(c) Reaction with Water: Different metals react with water at different temperatures to evolve out hydrogen. Some metals react with water at room temperature and some metals which are less active react with hot water while other metals react only with steam.

(i) Sodium, calcium react with water at room temperature. Sodium burns in water to give sodium hydroxide.

2Na    + 2H2O 2NaOH     + H2 ↑

Sodium    water   Sodium hydroxide

Ca    + 2H2O Ca(OH)2  + H2 ↑

Calcium   water  Calcium hydroxide

(ii) Iron, magnesium and zinc are not affected by cold water. They are reacted upon by steam only.

2Fe    + 4H2O Fe3O4      +   4H2 ↑

Iron Steam       Iron (II, III) oxide

Mg    + H2O    MgO     +   H2 ↑

Magnessium Steam        Magnesium oxide

Zinc and iron react very mildly with steam whereas copper, silver and nickel do not react with even steam.

(d) Reaction with Acids:

(i) With Hydrochloric Acid: Metals like sodium, magnesium, zinc, iron, react with hydrochloric acid to form metal chloride and hydrogen gas.

Zn    + 2HCl    ZnCl2      + H2 ↑

Zinc Zinc chloride

(ii) With Dilute Sulphuric Acid: More active metals when treated with dilute sulphuric acid give hydrogen.

Fe    + H2SO4 FeSO4     + H2  

Iron Iron Sulphate

Zn    + H2SO4    ZnSO4<