Acids, Bases and Salts · Lesson 9 of 12
More About Salts
“Salts have families too, and apparently even they inherit traits from their parents.”
• Identify common salts from their formulae. • Group salts into families using common positive or negative ions. • Identify possible parent acids and bases of salts. • Classify salt solutions as acidic, basic or neutral. • Relate salt pH to the strength of the acid and base from which the salt is formed.
A salt is not automatically neutral simply because it is called a salt. Salts form many families, and their solutions can be neutral, acidic or basic depending on the ions they contain and the acid-base combination from which they are formed.
Family Of Salts
| Salt | Formula |
|---|---|
| Potassium sulphate | K₂SO₄ |
| Sodium sulphate | Na₂SO₄ |
| Calcium sulphate | CaSO₄ |
| Magnesium sulphate | MgSO₄ |
| Copper sulphate | CuSO₄ |
| Sodium chloride | NaCl |
| Sodium nitrate | NaNO₃ |
| Sodium carbonate | Na₂CO₃ |
| Ammonium chloride | NH₄Cl |
Salts with a common positive ion or a common negative ion can be grouped into the same family.
Sodium chloride, sodium sulphate, sodium nitrate and sodium carbonate belong to the family of sodium salts because they contain sodium ions. Sodium chloride and potassium chloride belong to the family of chlorides because they contain chloride ions.
Identifying Parent Acids And Bases
The negative ion of a salt often points to the acid from which it can be formed, while the positive ion often points to the base. For example, chloride salts are associated with hydrochloric acid and sodium salts can be associated with sodium hydroxide.
pH Of Salts
Solutions of salts may be tested using litmus or pH paper. Some are neutral, some acidic and some basic. The result depends strongly on the nature of the acid and base that formed the salt.
| Parent Acid | Parent Base | Typical Nature Of Salt Solution |
|---|---|---|
| Strong acid | Strong base | Neutral |
| Strong acid | Weak base | Acidic |
| Weak acid | Strong base | Basic |
Sodium chloride is formed from hydrochloric acid and sodium hydroxide. Because both are strong, sodium chloride solution is approximately neutral.
Problem
A salt is formed from a strong acid and a weak base. What nature would you expect its aqueous solution to show?
- 1.Identify the parent acid as strong.
- 2.Identify the parent base as weak.
- 3.A salt formed from a strong acid and weak base generally gives an acidic solution.
- 4.Therefore the salt solution is expected to have pH below neutral.
Quiz
A salt formed from a strong acid and a weak base generally produces what type of aqueous solution?
Why are sodium chloride and sodium sulphate considered members of the same salt family?
What type of salt usually forms from a strong acid and a strong base?
A salt formed from a weak acid and a strong base generally gives what type of solution?
Practice Problems
- Write the formulae of potassium sulphate, sodium sulphate, calcium sulphate and ammonium chloride.
- Explain why sodium chloride and sodium sulphate belong to the same family of salts.
- Explain why sodium chloride and potassium chloride can also be grouped into one salt family.
- Predict the nature of a salt solution formed from a strong acid and weak base.
- Explain why sodium chloride solution is approximately neutral.
Key Takeaways
• Salts with a common positive ion or common negative ion can be grouped into families. • The ions in a salt can help identify the acid and base from which it may be formed. • Salt solutions may be acidic, basic or neutral. • A strong acid and strong base generally form a neutral salt. • A strong acid and weak base generally form an acidic salt. • A weak acid and strong base generally form a basic salt.