Problem 5 - Chemistry An Atoms First Approach

Question

Explain why salts can be acidic, basic, or neutral, and show examples. Do this without specific numbers.

Step-by-Step Solution

Answer

Salts can be acidic, basic, or neutral due to the interaction of their constituent ions with water through hydrolysis. Acidic salts result from strong acids and weak bases, where the cation undergoes hydrolysis, releasing a proton and increasing the concentration of hydronium ions (e.g., NH4Cl). Basic salts result from weak acids and strong bases, where the anion undergoes hydrolysis, releasing hydroxide ions and increasing the concentration of hydroxide ions (e.g., CH3COONa). Neutral salts result from strong acids and strong bases, where neither ion undergoes significant hydrolysis, maintaining a pH close to 7 (e.g., NaCl).

Step 1: Definition of Salts

A salt is the product of an acid-base reaction, in which an acid donates its proton (H+) to a base, and a base donates its hydroxide ion (OH-) to an acid. The remaining positive ion from the acid and the negative ion from the base combine to form the salt. For example, when hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH), a salt (sodium chloride, NaCl) and water (H2O) are formed.

Step 2: Hydrolysis of Salts in Water

When dissolved in water, the ions forming the salt can interact with the water molecules through a process called hydrolysis. This process can result in the formation of hydronium ions (H3O+) or hydroxide ions (OH-), which are responsible for the acidity or basicity (alkalinity) of the solution.

Step 3: Acidic Salts

Acidic salts are formed from the interaction of a strong acid with a weak base. In this case, the positive ion (cation) of the salt can undergo hydrolysis, releasing a proton (H+) to the water, which increases the concentration of hydronium ions (H3O+) in the solution. Consequently, the pH of the solution becomes less than 7, indicating that it is acidic. Example: Ammonium chloride (NH4Cl), formed by the reaction of hydrochloric acid (HCl, a strong acid) and ammonia (NH3, a weak base).

Step 4: Basic Salts

Basic salts are formed from the interaction of a weak acid with a strong base. In this case, the negative ion (anion) of the salt can undergo hydrolysis, releasing a hydroxide ion (OH-) to the water, which increases the concentration of hydroxide ions in the solution. Consequently, the pH of the solution becomes greater than 7, indicating that it is basic (alkaline). Example: Sodium acetate (CH3COONa), formed by the reaction of acetic acid (CH3COOH, a weak acid) and sodium hydroxide (NaOH, a strong base).

Step 5: Neutral Salts

Neutral salts are formed from the interaction of a strong acid with a strong base. In this case, neither the cation nor the anion of the salt undergoes significant hydrolysis, resulting in a solution with a pH close to 7 (neutral). Example: Sodium chloride (NaCl), formed by the reaction of hydrochloric acid (HCl, a strong acid) and sodium hydroxide (NaOH, a strong base). In summary, salts can be acidic, basic, or neutral, depending on their constituent ions and their interactions with water molecules through the process of hydrolysis.