6 CHEMICAL PROPERTIES OF METALS
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 + H2O 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 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
2K + 2H2O 2KOH + H2
Potassium Water Potassium hydroxide
Ca + 2H2O Ca(OH)2 + H2
Calcium Water Calcium hydroxide
- Magnesium, zinc and iron react with hot water to produce metal oxide and hydrogen gas.
Mg + H2O MgO + H2
Magnesium Water Magnesium oxide
Zn + H2O ZnO + H2
Zinc Water Zinc oxide
3Fe + 4H2O Fe3O4 + 4H2
Iron Water Iron oxide
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
Mg + 2HCl MgCl2 + H2
Magnesium Hydrochloric acid Magnesium chloride
Zn + 2HCl ZnCl2 + H2
Zinc Hydrochloric acid Zinc chloride
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 Copper nitrate Silver
(Colourless solution) (Blue solution) (White deposit)
Reaction of Zinc with Copper Sulphate Solution
If a piece of zinc metal is placed in 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 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 copper sulphate solution. So, zinc displaces copper from copper sulphate solution to form zinc sulphate and copper.
Zn + CuSO4 ZnSO4 + Cu
Zinc Copper sulphate Zinc sulphate Copper
(Blue solution) (colourless solution) (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 Iron sulphate Copper
(Blue solution) (Greenish sol) (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
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