When a metal reacts with water, it forms metal hydroxide. Hydrogen gas is also produced in this reaction. Following is the general equation for this reaction.
Metal + Water ⇨ Metal hydroxide + Hydrogen
Different metals react with water at different rates. Most of the metals do not react with water. However, alkali metals react vigorously with water.
The reaction between sodium and water is highly vigorous. When sodium reacts with water, sodium hydroxide and hydrogen are produced. This reaction is highly exothermic. So much heat evolves during the reaction that the reaction mixture catches fire. Following equation shows this reaction.
Na + H2O ⇨ NaOH + H2
As sodium is highly reactive, so it is kept stored under kerosene so that it does not get a chance to react with moisture which may be present in air. This is done in order to prevent any accidental fire.
When potassium reacts with water then potassium hydroxide and hydrogen gas are formed. Lot of heat is produced during this reaction. Following equation shows this reaction.
K + H2O ⇨ KOH + H2
When calcium reacts with water, then calcium hydroxide and hydrogen gas are formed. This too is an exothermic reaction. When bubbles of hydrogen gas stick to metal then calcium starts floating. Following equation shows this reaction.
Ca + 2H2O ⇨ Ca(OH)2 + H2
Magnesium does not react with cold water. It reacts with hot water and forms magnesium hydroxide and hydrogen gas. Magnesium starts floating due to hydrogen bubbles sticking to the meatl. Following equation shows this reaction.
Mg + 2H2O ⇨ Mg(OH)2 + H2
Image Ref: NCERT Textbook class 10 Science
When steam is passed over magnesium, the reaction becomes fast. Magnesium oxide and hydrogen gas are formed, in this reaction.
Mg + H2O ⇨ MgO + H2
Aluminium does not react with cold or hot water. But when steam is passed over aluminium, aluminium oxide and hydrogen gas are produced. Following equation shows this reaction.
2Al + 3H2O ⇨ Al2O3 + 2H2
Zinc does not react with cold or hot water. Zinc metal produces zinc oxide and hydrogen gas when steam is passed over it.
Zn + H2O ⇨ ZnO + H2
Reaction between iron and cold water too slow to be noticed. When iron reacts with atmospheric moisture, it forms rust (iron oxide). But this is a very slow reaction.
When steam is passed over iron then iron oxide and hydrogen gas are formed. Following equation shows this.
3Fe + 4H2O ⇨ Fe3O4 + 4H2
Lead, copper, silver and gold do not react with water at any temperature.
We can summarise the reaction of water with metals as follows:
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