DISPALCEMENT AND DOUBLE DECOMPOSITION REACTIONS

 DISPALCEMENT AND DOUBLE DECOMPOSITION REACTIONS
Chemical displacement reactions can be further classified as
Metal displacement reaction:
    A chemical displacement reaction in which a metal is displaced from the compound is known as metal displacement reaction.
For example ,
    When a strip of magnesium metal is placed in an aqueous solution of copper (II) nitrate,the grey magnesium metal strip will slowly disappear and we can observe a orange/brown precipitate of copper is observed.This is because magnesium replaces the copper. The products of the reaction are aqueous magnesium nitrate and solid copper metal.Now,this subcategory of single-replacement reactions is called a metal replacement reaction because it is a metal that is being replaced (copper).
The equation can be written as follows
Mg(s)+Cu(NO₃)₂(aq) Mg(NO₃)₂(aq)+Cu(s)
Hydrogen Replacement reactions:
    In a hydrogen replacement reaction, the hydrogen in the acid is replaced by an active metal.Many metals react easily with acids and replaces hydrogen which escapes as hydrogen gas.
For example 
    Zinc reacts with hydrochloric acid to produce aqueous zinc chloride and hydrogen.Here hydrogen in acid is replaced by zinc.Hence it is a hydrogen replacement reaction.  
The equation can be written as follows
                              Zn(s)+2HCl(aq)  ZnCl₂(aq)+H₂(g)
Some metals are so reactive that they are capable of replacing the hydrogen in water. The products of such a reaction are metal hydroxide and hydrogen gas. All group-1 metals undergo this type of reaction. For example,Sodium reacts vigorously with water to produce aqueous sodium hydroxide and hydrogen.
The equation can be written as follows
                              2Na(s)+2H₂O(l)  2NaOH(aq)+H₂(g)
Halogen displacement reactions:
    A chemical displacement reaction in which a halogen is displaced from the compound is known as halogen displacement reaction.
For example,
the element chlorine reacts with an aqueous solution of sodium bromide to produce aqueous sodium chloride and elemental bromine.
The equation can be written as follows
Cl₂(g)+2NaBr(aq) ---------> 2NaCl(aq)+Br₂(l)
The reactivity of the halogens decreases from top to bottom within the group(group 17). Fluorine is the most reactive halogen, while iodine is the least. Since chlorine is above bromine, it is more reactive than bromine and can replace it in a halogen replacement reaction
EXPERIMENT
Let us perform an activity using copper sulphate solution and iron nails to understand the chemical displacement reactions as follow
The equation is as follow
\(CuS{O_4} + Fe \to FeS{O_4} + Cu\)
Copper Sulphate + Iron  Ferrous Sulphate + Copper
Activity: Experiment:
Apparatus:    Beaker
Chemicals:    Copper sulphate, a shining iron nail
Procedure:    Take copper sulphate powder in a beaker and add water so to make sulphate solution. Place the iron nail in the solution.Observe after sometime what happens in the beaker.
Observation: Red deposit is formed on the iron nail. The blue solution turns light green in colour.
Conclusion: The copper atom in copper sulphate molecule is displaced by iron atom and occupies its palce. So Ferrous sulphate is formed in the solution. So the original blue solution turns light green. The displaced copper form copper sulphate deposits on the iron nail. The deposit is red in colour.
Chemical Equation:   Copper Sulphate + Iron  Ferrous Sulphate + Copper
\(CuS{O_4} + Fe \to FeS{O_4} + Cu\)(deposit)