What is a neutralisation reaction? Give two examples.

An acid-base reaction, also known as a neutralisation reaction, occurs when an acid and a base interact chemically to produce a salt and water. This type of reaction is vital in various applications, from industrial processes to biology. The general equation for an acid-base reaction is given by:
\[ \text{Acid} + \text{Base} \rightarrow \text{Salt} + \text{Water} \]
Acids are substances that can donate a proton (H⁺). Bases are substances that can accept a proton. When they react, the hydrogen ions (\text {H⁺}) from the acid combine with the hydroxide ions (\text{OH^-}) from the base to form water (\text{H₂O}).
Examples include:

• Hydrochloric acid with sodium hydroxide: \[ \text{HCl} + \text{NaOH} \rightarrow \text{NaCl} + \text{H}_2\text{O} \]
• Sulfuric acid with potassium hydroxide: \[ \text{H}_2\text{SO}_4 + 2 \text{KOH} \rightarrow \text{K}_2\text{SO}_4 + 2 \text{H}_2\text{O} \]

An important note is that during this reaction, heat is often released, making it an exothermic process.

In a neutralisation reaction, one of the main products is a salt. Salts are ionic compounds that result from the neutralisation of an acid by a base. These compounds are formed when the cation from the base and the anion from the acid combine.

For example:

• In the reaction of hydrochloric acid with sodium hydroxide, sodium chloride (\text{NaCl}) is formed: \[ \text{HCl} + \text{NaOH} \rightarrow \text{NaCl} + \text{H}_2\text{O} \]
• In the reaction of sulfuric acid with potassium hydroxide, potassium sulfate (\text{K}_2\text{SO}_4) is formed: \[ \text{H}_2\text{SO}_4 + 2 \text{KOH} \rightarrow \text{K}_2\text{SO}_4 + 2 \text{H}_2\text{O} \]

Salts can have a variety of properties depending on the specific acid and base that react. Some salts are soluble in water, while others are not. They are essential in various fields such as chemistry, biology, and medicine.

Water production is a critical aspect of the neutralisation reaction. When an acid reacts with a base, the hydrogen ions (\text{H⁺}) from the acid combine with the hydroxide ions (\text{OH^-}) from the base to produce water (\text{H₂O}). This process is exothermic, releasing energy in the form of heat.

This can be represented in any neutralisation reaction as:
\[ \text{H⁺} + \text{OH^-} \rightarrow \text{H}_2\text{O} \]
In the examples given:

• Hydrochloric acid with sodium hydroxide: \[ \text{HCl} + \text{NaOH} \rightarrow \text{NaCl} + \text{H}_2\text{O} \]
• Sulfuric acid with potassium hydroxide: \[ \text{H}_2\text{SO}_4 + 2 \text{KOH} \rightarrow \text{K}_2\text{SO}_4 + 2 \text{H}_2\text{O} \]

Water is vital for life and plays a fundamental role in chemical reactions. Understanding water formation during neutralisation helps in comprehending many biological and environmental processes, including maintaining the pH balance in living organisms and ecosystems.