Acidic, Basic and Neutral Salts

This is part of the HSC Chemistry course under the topic Quantitative Analysis.

HSC Chemistry Syllabus

write ionic equations to represent the dissociation of acids and bases in water, conjugate acid/base pairs in solution and amphiprotic nature of some salts, for example:

– sodium hydrogen carbonate

– potassium dihydrogen phosphate

What are Acidic, Basic and Neutral Salts?

This video explores the acidic, basic and neutral nature of various salts. You will learn how to identify these different types of salts.

What are Salts?

Salts are ionic compounds produced from an acid-base reaction.

Many salts, despite being neutrally charged, produce acidic and basic solutions when dissolved in water.

The properties of acidic and basic salts can be understood using the Brønsted-Lowry acid/base theory.

Acidic Salts

Acidic salts are acidic because they contain conjugate acids of weak bases.

An example of an acidic salt is ammonium chloride, which is formed from the neutralisation between hydrochloric acid and ammonia:

$$HCl(aq) + NH_3(aq) \rightarrow NH_4Cl(aq)$$

Ammonium is the conjugate acid of ammonia (weak base). Ammonium ions are Brønsted-Lowry acids as they donate protons to water:

$$NH_4^+(aq) + H_2O(l) \rightleftharpoons NH_3(aq) + H_3O^+(aq)$$

The production of hydronium ions causes a solution of ammonium chloride to become acidic. Chloride ions are spectator ions and thus do not contribute to the pH of the solution.

Acidic salts such as ammonium chloride are not Arrhenius acids as they do not contain and dissociate to produce hydrogen ions.

Other examples of acidic salts include:

Ammonium nitrate
Ammonium sulfate

Basic Salts

Basic salts are basic because they contain conjugate bases of weak acids.

An example of a basic salt is sodium acetate, which is formed from the neutralisation between acetic acid and sodium hydroxide:

$$CH_3COOH(aq) + NaOH(aq) \rightarrow NaCH_3COO(aq) + H_2O(l)$$

Acetate is the conjugate base of acetic acid (weak acid). Acetate ions are Brønsted-Lowry bases as they accept proton from water:

$$CH_3COO^-(aq) + H_2O(l) \rightleftharpoons CH_3COOH(aq) + OH^-(aq)$$

The production of hydroxide ions causes a solution of sodium acetate to become basic. Sodium ions are spectator ions and thus do not contribute to the pH of the solution.

Basic salts such as sodium acetate are not Arrhenius bases as they do not contain and dissociate to produce hydroxide ions.

Other examples of basic salts include:

Potassium acetate
Sodium fluoride
Sodium hypochlorite
Sodium citrate

Neutral Salts

Neutral salts are neutral because they contain neither of conjugate acids of weak bases or conjugate bases of weak bases.

Neutral salts are typically formed from neutralisation between strong acids and strong bases.

An example of a neutral salt is sodium chloride, which is formed from the neutralisation between hydrochloric acid and sodium hydroxide:

$$HCl(aq) + NaOH(aq) \rightarrow NaCl(aq) + H_2O(l)$$

Sodium and chloride ions are both spectator ions. Chloride ions are unable to accept protons from water because they are the conjugate base of hydrochloric acid which is a strong acid. Strong acids like HCl completely dissociate in water:

$$HCl(aq) \rightarrow H^+(aq) + Cl^-(aq)$$

Sometimes a neutral salt can be formed from the neutralisation between a strong acid and weak base. For example, the reaction between hydrochloric acid and sodium carbonate (weak base) produces sodium chloride:

$$HCl(aq) + Na_2CO_3(aq) \rightarrow NaCl(aq) + H_2O(l) + CO_2(g)$$

Other examples of neutral salts include:

Potassium chloride
Sodium nitrate
Potassium nitrate