Our Objective

To study a single displacement reaction with the help of iron nails and copper sulphate solution.

Theory

What is a displacement reaction?

Displacement reaction is a chemical reaction in which a more reactive element displaces a less reactive element from its compound. Both metals and non-metals take part in displacement reactions.

Example : Reaction of iron nails with copper sulphate solution.

How is the chemical reactivity of metals linked with their position in the electrochemical series?

Chemical reactivity of metals is linked with their relative positions in the activity series. Certain metals have the capacity to displace some metals from the aqueous solutions of their salts.A metal placed higher in the activity series can displace the metal that occupies a lower position from the aqueous solution of its salt. The displacement reaction is not limited to metals only. Even non-metals can take part in these reactions.

Examples are halogens. The activity series of halogen is F > Cl > Br > I.

Note the point:

An important thing to remember with single displacement reaction is that elements that form cations can only displace cations and elements that form anions can only displace anions.

Classification of single displacement reaction:

• Anion replacement reaction
• Cation replacement reaction

(A) Cation Replacement Reaction

In this reaction, one cation replaces another one from its solution. A cation is a positively charged ion or metal. All metal displacement reactions are cation replacement reactions.

Let us demonstrate some examples of cation replacement reactions.

• If a strip of magnesium metal is placed in copper sulphate solution, the blue colour of copper sulphate disappears and the magnesium metal turns brown as the displaced copper is deposited on it. In the reactivity series, the position of magnesium is above that of copper. So it is more reactive than copper and it would displace copper from copper sulphate solution.

• Also metals like Zn, Al, Pb, Fe, etc., displace Cu from copper salt solution. The chemical reaction can be written as:

• Iron displaces lead from the aqueous solution of lead nitrate.                                                                                                                                                              

• Similarly, metals above hydrogen in the reactivity series displace hydrogen from dilute acids.               

For example :The metals such as potassium, sodium, lithium, etc. react more vigorously with dilute acids forming metal salts and hydrogen gases.   

• Metals such as aluminium, zinc, magnesium, iron, etc., react safely with dilute acids.  

For example,

           

The reaction Zn with dil. H₂SO₄ is often used in the laboratory for the preparation of hydrogen gas.                                                        

If a less reactive metal is added to a salt solution of more reactive metal, nothing will happen.  

(B) Anion Replacement Reactions 

In this reaction, one anion replaces another one from its solution. An anion is a negatively charged ion or non-metal.  For example, more reactive halogen replaces less reactive halogen from its solution.

• Chlorine displaces bromine from an aqueous solution of sodium bromide.

• Bromine splaces iodine from potassium iodide solution.

Learning Outcomes

1. Students acquire good understanding about concepts like single displacement reaction, and cationic replacement reactions.
2. Students classify the metals that can displace the other metals from salt solutions.
3. Students develop the skill to demonstrate a single displacement reaction using iron nails and copper sulphate solution.
4. Students will be able to distinguish a single displacement reaction from a given set of chemical reactions.

Here, we will discuss the reaction between iron nails and copper sulphate solution.