Question

The phenomenon of interaction of anions and cations furnished by clectrolyte with ${\mathrm{II}}^{+}$ and OIT - ions of water to producc acidic nature or alkalinity is known as hydrolysis. In hydrolysis(1) The $\mathrm{pH}$ may either increase or decrease (2) All the salts (except those made up with strong acid and base) undergo hydrolysis (3) The variation of $\mathrm{pH}$ depends upon the nature of salt as well as on the temperature (4) All

Short answer

Statement 4: All

Step-by-step solution

Understand the Concept

Hydrolysis is the reaction of anions and cations from salts with water, which can result in changes in the pH of the solution. This can make the solution either more acidic or more alkaline.

Analyze Statement 1

Statement 1 says the pH may either increase or decrease during hydrolysis. This is true because depending on the salt and its interaction with water, the solution can become acidic (lower pH) or basic (higher pH).

Analyze Statement 2

Statement 2 says that all salts (except those made from strong acids and bases) undergo hydrolysis. This is also true because salts formed from the reaction of a strong acid and a weak base, or a weak acid and a strong base, will undergo hydrolysis, unlike salts formed by strong acids and strong bases which do not change the pH significantly.

Analyze Statement 3

Statement 3 states that the variation of pH depends on the nature of the salt and the temperature. This is true as well, since both the type of salt and the temperature can influence the degree of hydrolysis and thus affect the pH.

Analyze Statement 4

Statement 4 says 'All', meaning it implies all the given statements (1, 2, and 3) are correct. Since we've analyzed each previous statement and found them to be true, statement 4 by extension is also correct.

Key concepts

Anion-Cation Interactions

In the process of hydrolysis, anions and cations from salts interact with water. These interactions play a critical role in determining the properties of the solution.

When a salt dissociates in water, it separates into its constituent anions and cations. The nature of these ions influences how they will interact with water molecules. For instance:

• Anions (negative ions) can react with the hydrogen ions ${\text{H}}^{+}$ from water.
• Cations (positive ions) can react with the hydroxide ions ${\text{OH}}^{-}$ from water.

These reactions result in the consumption or production of ${\text{H}}^{+}$ and ${\text{OH}}^{-}$ ions, which ultimately affects the \text{pH} of the solution. For example,
• \textbf{Cations from weak bases} can hydrolyze to produce ${\text{H}}^{+}$, making the solution acidic.
• \textbf{Anions from weak acids} can hydrolyze to produce ${\text{OH}}^{-}$, making the solution alkaline.
Understanding these interactions helps in predicting the behavior of a solution when a specific salt is dissolved in water.

pH Variation

pH is a measure of the acidity or alkalinity of a solution. It can change during hydrolysis of salts. The key points are:

• \textbf{Acidic solutions} have a \text{pH} less than 7.
• \textbf{Basic solutions} (alkaline) have a \text{pH} greater than 7.
• \textbf{Neutral solutions} have a \text{pH} equal to 7.

The \text{pH} of a solution during hydrolysis depends on:

• \textbf{The nature of the salt}: If the salt comes from a strong acid and weak base, the solution becomes acidic. If the salt comes from a weak acid and strong base, the solution becomes basic.
• \textbf{Temperature}: Temperature can affect the degree of ionization and the extent of hydrolysis, thereby altering the \text{pH} of the solution.

For example:

• \textbf{Weak acid and strong base (e.g. sodium acetate)}: Dissolving this salt in water will produce ${\text{OH}}^{-}$, making the solution alkaline.
• \textbf{Strong acid and weak base (e.g. ammonium chloride)}: Dissolving this salt in water will produce ${\text{H}}^{+}$, making the solution acidic.

This is why not all salts have the same effect on \text{pH}.

Salt Hydrolysis

Salt hydrolysis is the process where a salt interacts with water to produce an acidic or basic solution. Most salts undergo hydrolysis, except those made from strong acids and strong bases. Let's break down how these reactions work:

• Salts from strong acids and weak bases: These produce an acidic solution because the cation from the weak base interacts with water to release ${\text{H}}^{+}$.
• Salts from weak acids and strong bases: These produce a basic solution as the anion from the weak acid interacts with water to release ${\text{OH}}^{-}$.
• Neutral salts: Those derived from strong acids and strong bases, such as NaCl, do not hydrolyze and thus do not change the \text{pH} of the water significantly.

The degree of hydrolysis and thus the resultant \text{pH} of the solution also depend on various factors including:

• Concentration of the salt solution
• Temperature of the solution

For instance, increasing temperature can enhance hydrolysis for some salts, leading to a greater change in \text{pH}. Understanding salt hydrolysis is essential for predicting and controlling the properties of solutions in various chemical processes.