Acids, Bases and Salts · Lesson 5 of 12
What Do All Acids And All Bases Have In Common?
“The secret behind acids and bases turns out to be tiny charged particles doing all the work.”
• Explain why acidic and basic solutions conduct electricity. • Explain why hydrogen-containing compounds are not necessarily acids. • Relate acidic character to hydrogen ions in aqueous solution. • Relate basic character to hydroxide ions in aqueous solution. • Distinguish a base from an alkali.
Hydrochloric acid, sulphuric acid and acetic acid are different substances, yet they show many similar chemical properties. The common feature is not simply that their formulae contain hydrogen. Their similar behaviour appears when they form ions in water.
Electrical Conductivity Of Acidic Solutions
A simple conductivity circuit can contain a battery, bulb, switch and two electrodes dipped into a solution. Dilute hydrochloric acid and dilute sulphuric acid allow current to pass, so the bulb glows. Glucose and alcohol solutions do not make the bulb glow under the same conditions.
An Ion is an electrically charged particle formed when an atom or group of atoms carries a net positive or negative charge.
Electric current through an aqueous acid is carried by moving ions. This explains why acidic solutions conduct electricity while solutions that do not form suitable ions conduct poorly.
Hydrogen Ions And Acidic Character
Acids produce hydrogen ions in aqueous solution. Different acids also contain different negative ions. Hydrochloric acid gives chloride ions, nitric acid gives nitrate ions, sulphuric acid gives sulphate ions and acetic acid gives acetate ions. The common positive ion associated with acidic behaviour is hydrogen ion.
| Acid | Characteristic Negative Ion |
|---|---|
| Hydrochloric acid | Cl⁻ |
| Nitric acid | NO₃⁻ |
| Sulphuric acid | SO₄²⁻ |
| Acetic acid | CH₃COO⁻ |
Why Glucose And Alcohol Are Not Acids
Glucose and alcohol contain hydrogen atoms, but they do not produce hydrogen ions in water in the way acids do. Their hydrogen remains bonded inside neutral molecules. The presence of hydrogen in a chemical formula alone is therefore not sufficient to classify a compound as an acid.
Hydroxide Ions And Basic Character
Bases that dissolve or dissociate in water produce hydroxide ions. Hydroxide ions are responsible for the characteristic basic behaviour of aqueous basic solutions.
An Alkali is a base that dissolves in water and produces hydroxide ions in aqueous solution.
Every alkali is a base, but every base is not necessarily an alkali because some bases do not dissolve sufficiently in water.
Quiz
Why do aqueous acid solutions conduct electricity?
Which ion is responsible for acidic character in aqueous solution?
Which ion is responsible for the basic character of an aqueous solution?
Why is glucose not classified as an acid even though it contains hydrogen?
Practice Problems
- Explain why hydrochloric acid solution conducts electricity.
- Explain why glucose solution does not show acidic behaviour even though glucose contains hydrogen.
- Name the negative ions associated with hydrochloric acid, nitric acid, sulphuric acid and acetic acid.
- Explain how hydroxide ions are connected with the basic nature of a solution.
- Distinguish between a base and an alkali.
Key Takeaways
• Aqueous acid and base solutions can conduct electricity because they contain mobile ions. • Acidic character is associated with the formation of H⁺ or H₃O⁺ ions in water. • Basic character is associated with the formation of OH⁻ ions in water. • The presence of hydrogen in a formula alone does not make a compound an acid. • An alkali is a base that dissolves in water and produces hydroxide ions.