Question

Thc pair of salts that does not hydrolyze (1) \(\mathrm{FcCl}_{3}, \mathrm{Sn} \mathrm{Cl}_{4}\) (2) \(\mathrm{CaCl}_{2}, \mathrm{~K}_{2} \mathrm{SO}_{4}\) (3) \(\mathrm{CuSO}_{4}, \Lambda 1 \mathrm{Cl}_{3}\) (4) \(\mathrm{NII}_{4} \mathrm{Cl}, \mathrm{Na}_{2} \mathrm{CO}_{3}\)

Short answer

CaCl2 and K2SO4 do not hydrolyze.

Step-by-step solution

Definition of Hydrolysis

Hydrolysis is the chemical reaction between a salt and water, often creating an acidic or basic solution. A salt derived from a strong base and strong acid typically does not hydrolyze.

Analyze Each Salt Pair

Examine each pair to determine if they are derived from strong acids and bases.

Pair 1 - FcCl3, SnCl4

Both salts are derived from weak bases and strong acids. Therefore, these salts will hydrolyze.

Pair 2 - CaCl2, K2SO4

CaCl2 and K2SO4 are derived from strong bases (Ca(OH)2 and KOH) and strong acids (HCl and H2SO4) respectively. These salts will not hydrolyze.

Pair 3 - CuSO4, AlCl3

Both salts are derived from weak bases and strong acids. Therefore, these salts will hydrolyze.

Pair 4 - NH4Cl, Na2CO3

NH4Cl is derived from a weak base (NH3) and a strong acid (HCl), and Na2CO3 is derived from a strong base (NaOH) and a weak acid (H2CO3). Therefore, these salts will hydrolyze.

Conclusion

The pair that does not hydrolyze is CaCl2 and K2SO4.

Key concepts

Salt Chemistry

Salt chemistry involves the study of salts, which are compounds formed from the neutralization reaction of an acid and a base. Salts can be composed of positive ions (cations) from a base and negative ions (anions) from an acid. This means salts have a wide range of properties and behaviors. For example, salt NaCl (table salt) is neutral, while other salts can be acidic or basic depending on their component ions. Understanding the behavior of different salts is crucial because it helps us predict their reactions, like hydrolysis, which we'll explore next.

Hydrolysis Reaction

Hydrolysis is a chemical reaction where water breaks down compounds. In the context of salts, hydrolysis occurs when salts react with water, potentially creating acidic or basic solutions. This happens because the ions in the salt interact with water molecules.
The key point here is that not all salts hydrolyze. Generally, salts derived from strong acids and strong bases do not hydrolyze. This is because the ions formed are neither strong enough acids nor strong enough bases to react with water. For example, in our exercise, CaCl2 and K2SO4 don't hydrolyze since they come from strong acids and strong bases.

Strong Acids and Bases

Strong acids and bases are substances that completely dissociate into their ions in water. Examples of strong acids include hydrochloric acid (HCl), sulfuric acid (H2SO4), and nitric acid (HNO3). Strong bases include sodium hydroxide (NaOH) and potassium hydroxide (KOH).
The complete dissociation means that in an aqueous solution, these substances exist entirely as their constituent ions without any remaining original molecules. This property influences the behavior of the salts they form. When salts are derived from these strong acids and bases, they typically do not hydrolyze because their ions are stable and do not react further with water.

Salts Derived from Strong Bases and Strong Acids

Salts that come from the reaction of strong bases with strong acids generally do not undergo hydrolysis. This is because both the cation and anion are stable and do not interact with water to form either an acidic or basic solution.
Let's consider the solution exercise: CaCl2 and K2SO4. Both are examples of such salts. CaCl2 is derived from calcium hydroxide (a strong base) and hydrochloric acid (a strong acid), and K2SO4 is derived from potassium hydroxide (strong base) and sulfuric acid (strong acid). Therefore, these salts simply dissolve in water without reacting further, resulting in neutral solutions.
Understanding this helps predict and explain why certain pairs of salts like CaCl2 and K2SO4 do not hydrolyze, while others do.