Metals are also called electropositive elements because the metal atoms form positively charged ion by losing electrons. Following are the important chemical reactions of metals which takes place due to the electropositive character of metals.
1. Reaction of Metals with Oxygen
Almost all metals react with oxygen to form metal oxides. But different metals react with oxygen at different intensities. For example, sodium metal is always kept immersed in kerosene oil. Because, if we keep it open, it reacts so vigorously with oxygen present in air that it catches fire. We have already discussed that the oxides of metals are basic in nature. As all the metals have different reactivity so they combine with oxygen at different temparature.
Sodium metal reacts with oxygen of air at room temperature to form basic sodium oxide.
4Na + O2 → 2Na2O
(Sodium + Oxygen → Sodium oxide)
On heating, magnesium metal burns in air giving magnesium oxide.
2Mg + O2 → 2MgO
(Magnesium + Oxygen → Magnesium oxide)
Zinc metal burns in air only on strong heating to form zinc oxide.
2Zn + O2 → 2ZnO
(Zinc + Oxygen → Zinc oxide)
Generally, metal oxides are insoluble in water. But some metal oxides are able to dissolve in water to form metal hydroxides (or alkali). For example, oxides of sodium and potassium dissolve in water to form sodium hydroxide and potassium hydroxide respectively.
Na2O + H2 O → 2NaOH
(Sodium oxide + Water → Sodium hydroxide)
K2O + H2O → 2KOH
(Potassium oxide + Water → Potassium hydroxide)
In the same way sulphur reacts with oxygen of air to form acidic sulphur dioxide.
S + O2 → SO2
(Sulphur + Oxygen → Sulphur Dioxide)
2. Reaction of Metals with Water
Metals react with water to produce metal oxide (or metal hydroxide) and hydrogen gas. But, all metals do not react with water at equal intensity. The metals which are very reactive can react even with cold water while the other metals react with hot water or with steam. For example:
Sodium, potassium and calcium metal can react with cold water to produce their hydroxides and hydrogen gas.
2Na + 2H2O → 2NaOH + H2
(Sodium + Water → Sodium hydroxide + Hydrogen)
2K + 2H2O → 2KOH + H2
(Potassium + Water → Potassium hydroxide + Hydrogen)
Ca + 2H2O → Ca(OH)2 + H2
(Calcium + Water → Calcium hydroxide + Hydrogen)
Magnesium, zinc and iron react with hot water to produce metal oxide and hydrogen gas.
Mg + H2O → MgO + H2
(Magnesium + Water → Magnesium oxide + Hydrogen)
Zn + H2O → ZnO + H2
(Zinc + Water → Zinc oxide + Hydrogen)
3Fe + 4H2O → Fe3O4 + 4H2
(Iron + Water → Iron oxide + Hydrogen)
3. Reaction of Metals with Dilute Acids
When a metal reacts with a dilute acid then a metal salt and hydrogen gas are formed. For example: Sodium, magnesium and zinc reacts with dilute hydrochloric acid to form their salts and hydrogen gas.
2Na + 2HCl → 2NaCl + H2
(Sodium + Hydrochloric acid → Sodium chloride + Hydrogen)
Mg + 2HCl → MgCl2 + H2
(Magnesium + Hydrochloric acid → Magnesium chloride + Hydrogen)
Zn + 2HCl → ZnCl2 + H2
(Zinc + Hydrochloric acid → Zinc chloride + Hydrogen)
4. Reaction of Metals with Salt Solutions
If a more reactive metal is put in the salt solution of a less reactive metal, the more reactive metal displaces the less reactive metal from its salt solution. These reactions are called displacement reaction. For example:
Reaction of Copper with Silver Nitrate Solution.
If a piece of copper metal is placed in colourless solution of silver nitrate for some time, the colour of the solution becomes blue and a shining white deposit of silver metal is formed on the piece of copper. Actually, in this reaction copper metal is more reactive than silver present in silver nitrate solution. So, copper displaces silver from silver nitrate solution to form copper nitrate and silver metal.
Cu + 2AgNO3 → Cu(NO3)2 + 2Ag
(Copper + Silver nitrate(Colourless solution) → Copper nitrate(Blue solution) + Silver(White deposit))
Reaction of Zinc with Copper Sulphate Solution
If a piece of zinc metal is placed in a blue coloured solution of copper sulphate for some time, the blue colour of copper sulphate solution fades away. This happens due to the formation of a colourless solution of zinc sulphate .you will also observe that during this reaction red-brown copper metal deposits on the piece of zinc.
In this reaction zinc is more reactive metal than copper present in a copper sulphate solution. So, zinc displaces copper from copper sulphate solution to form zinc sulphate and copper.
Zn + CuSO4 → ZnSO4 + Cu
(Zinc + Copper sulphate(Blue solution) → Zinc sulphate(colourless solution) + Copper(red-brown))
Reaction of Iron with Copper Sulphate Solution
If iron fillings are placed in the blue coloured solution of CuSO4 for some time, the blue colour of copper sulphate solution turns into greenish colour and red brown precipitate of copper get deposited over iron fillings.
Fe + CuSO4 → FeSO4 + Cu
(Iron + Copper sulphate(Blue solution) → Iron sulphate(Greenish sol) + Copper(red-brown))
5. Reaction of Metals with Chlorine
All metals react with chlorine to form ionic metal chlorides. For example:
2Na + Cl2 → 2NaCl
(Sodium + Chlorine → Sodium chloride)
Ca + Cl2 → CaCl2
(Calcium + Chlorine → Calcium chloride)
Mg + Cl2 → MgCl2
(Magnesium + Chlorine → Magnesium chloride)
Zn + Cl2 → ZnCl2
(Zinc + Chlorine → Zinc chloride)
6. Reaction of Metals with Hydrogen
Only a few metals like Na, K, Ca and Mg react with hydrogen to form metal hydrides.
2Na + H2 → 2NaH
(Sodium + Hydrogen → Sodium hydrides)
Ca + H2 → CaH2
(Calcium + Hydrogen → Calcium hydrides)
Test your understanding and answer these questions:
- What are metals and nonmetals?