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When salts like \(\mathrm{NaNO}_3\) dissolve in water, they form a solution that is considered neutral. This is because \(\mathrm{NaNO}_3\) originates from a reaction between a strong acid, nitric acid (\(\mathrm{HNO}_3\)), and a strong base, sodium hydroxide (\(\mathrm{NaOH}\)). In solutions where both the acid and base are strong, their ions fully dissociate in water.
This dissociation does not affect the concentration of hydrogen ions \( (\mathrm{H}^+) \) or hydroxide ions \( (\mathrm{OH}^-) \) in the water. Therefore, the pH of the solution remains neutral, around 7, as there is no net increase or decrease in \(\mathrm{H}^+\) or \(\mathrm{OH}^-\) ion concentration.

• Strong acid + strong base = neutral solution
• pH ≈ 7
• No hydrolysis occurs

Thus, neutral solutions like the one formed by \(\mathrm{NaNO}_3\) are stable and do not experience any hydrolysis, ensuring they stay neutral unless other chemicals are introduced.

Salts like \(\mathrm{CaC}_2\mathrm{O}_4\) can create basic solutions when dissolved in water. This salt results from the reaction between the strong base calcium hydroxide (\(\mathrm{Ca(OH)}_2\)) and the weak acid oxalic acid. When \(\mathrm{CaC}_2\mathrm{O}_4\) dissolves, the oxalate ion \( (\mathrm{C}_2\mathrm{O}_4^{2-}) \) undergoes hydrolysis.
The process can be described by the equation: \[ \mathrm{C}_2\mathrm{O}_4^{2-} + \mathrm{H}_2\mathrm{O} \rightleftharpoons \mathrm{HC}_2\mathrm{O}_4^- + \mathrm{OH}^- \] This reaction produces additional hydroxide ions \( (\mathrm{OH}^-) \), which increases the pH of the solution, making it slightly basic, usually greater than 7.

• Weak acid + strong base = basic solution
• pH > 7 due to \(\mathrm{OH}^-\) production
• Hydrolysis increases basicity

Therefore, the salt's hydrolysis leads to an environment where the presence of \(\mathrm{OH}^-\) ions predominates, which is typical for basic solutions.

The dissolution of \(\mathrm{C}_5\mathrm{H}_5\mathrm{NHCl}\) in water results in an acidic solution. This salt is formed from a weak base, pyridine \( (\mathrm{C}_5\mathrm{H}_5\mathrm{N}) \), reacting with a strong acid, hydrochloric acid (HCl). The important species to consider is the pyridinium ion \( (\mathrm{C}_5\mathrm{H}_5\mathrm{NH}^+) \), which undergoes hydrolysis in water.
The reaction can be expressed as follows: \[ \mathrm{C}_5\mathrm{H}_5\mathrm{NH}^+ + \mathrm{H}_2\mathrm{O} \rightleftharpoons \mathrm{C}_5\mathrm{H}_5\mathrm{N} + \mathrm{H}_3\mathrm{O}^+ \] Here, the release of hydronium ions \( (\mathrm{H}_3\mathrm{O}^+) \) lowers the pH of the solution, making it acidic, typically less than 7.

• Weak base + strong acid = acidic solution
• pH < 7 due to \(\mathrm{H}_3\mathrm{O}^+\) production
• Hydrolysis increases acidity

Thus, the solution becomes more acidic due to the hydrolysis reaction, characterized by an increase in \(\mathrm{H}_3\mathrm{O}^+\) which leads to a decrease in pH.