Example of Double Displacement Reaction: Formation of Sodium Chloride (NaCl)

**Introduction**
A double displacement reaction, also known as a metathesis reaction, occurs when two compounds exchange their positive and negative ions to form two new compounds. In this type of reaction, the cations and anions of the reactants switch places to form new combinations. One common example of a double displacement reaction is the formation of sodium chloride (NaCl) from the reaction between sodium hydroxide (NaOH) and hydrochloric acid (HCl).

**Chemical Equation**
The chemical equation for this reaction can be represented as follows:

NaOH + HCl → NaCl + H₂O

**Explanation**
1. Sodium hydroxide (NaOH) is a strong base, while hydrochloric acid (HCl) is a strong acid. When these two substances are mixed together, a double displacement reaction occurs.
2. The sodium hydroxide dissociates into sodium ions (Na⁺) and hydroxide ions (OH⁻), while the hydrochloric acid dissociates into hydrogen ions (H⁺) and chloride ions (Cl⁻).
3. In the reaction, the sodium ions from sodium hydroxide combine with the chloride ions from hydrochloric acid to form sodium chloride (NaCl). This is because sodium (Na⁺) has a positive charge, while chloride (Cl⁻) has a negative charge, allowing them to attract and bond together.
4. The hydrogen ions from hydrochloric acid combine with the hydroxide ions from sodium hydroxide to form water (H₂O). This occurs because hydrogen (H⁺) has a positive charge and hydroxide (OH⁻) has a negative charge, enabling them to bond and create a neutral water molecule.
5. As a result, sodium chloride (NaCl) and water (H₂O) are formed as the products of the reaction.

**Conclusion**
The double displacement reaction between sodium hydroxide and hydrochloric acid results in the formation of sodium chloride and water. This reaction exemplifies the exchange of positive and negative ions between the reactants, leading to the formation of new compounds. Double displacement reactions are commonly observed in various chemical reactions and play a crucial role in the formation of different compounds.

BaCl2 (aq) + CuSO4 (aq) - BaSO4 (s) + CuCl2(aq)

In this double displacement reaction, two compounds, Barium Chloride and copper sulphate, react by an exchange of their ions to form two new compounds Barium sulphate and copper chloride.So, it is an example of double displacement reaction. Here, Barium sulphate formed in the form of white precipitate. So, it is also an example of precipitation reaction.

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