Which of the following statements is incorrect?

Options

A. The degree of ionisation of a weak electrolyte increases with dilution
B. Strong electrolyte are ionised complete at all concentrations
C. Addition of `NH_4Cl to NH_4OH` increases the ionisation of the letter
D. Increases of temperature increases the ionisation

Answer

To determine which statement is incorrect, let's analyze each statement one by one:

1. **Statement 1**: "The degree of ionization of a weak electrolyte increases with dilution."
- **Analysis**: This statement is true. As a weak electrolyte is diluted, the concentration of ions decreases, which shifts the equilibrium to the right according to Le Chatelier's principle, leading to an increase in the degree of ionization.

2. **Statement 2**: "Strong electrolytes are ionized completely at all concentrations."
- **Analysis**: This statement is also true. Strong electrolytes, such as NaCl, dissociate completely into their ions regardless of the concentration, meaning they are fully ionized.

3. **Statement 3**: "Addition of NH4Cl to NH4OH increases the ionization of later."
- **Analysis**: This statement is incorrect. When NH4Cl (which provides NH4+ ions) is added to NH4OH, it introduces a common ion (NH4+). According to Le Chatelier's principle, the presence of a common ion will shift the equilibrium of the dissociation of NH4OH to the left, thereby decreasing its ionization. Therefore, the ionization of NH4OH does not increase; it actually decreases.

4. **Statement 4**: "Increase of temperature increases the ionization."
- **Analysis**: This statement is generally true for most weak electrolytes. Increasing the temperature typically provides more energy to the system, which can lead to an increase in ionization as the forces of attraction between ions are overcome.

**Conclusion**: The incorrect statement is **Statement 3**: "Addition of NH4Cl to NH4OH increases the ionization of later."