Key Concepts
- 1What is pH scale?
- 2What is a neutralisation reaction?
Important Formulas & Facts
Scale from 0-14 measuring H⁺ ion concentration. pH < 7 = acidic, pH = 7 = neutral, pH > 7 = basic. Our blood pH is 7.35-7.45 (slightly basic).
Acid + Base → Salt + Water. Example: HCl + NaOH → NaCl + H₂O. Exothermic reaction. Used in antacids (Mg(OH)₂ neutralises stomach acid).
Must-Know Questions
Q1Which of the following is a strong acid?
HCl (hydrochloric acid) is a strong acid because it completely dissociates into ions in water. Acetic acid (CH₃COOH) is a weak acid. NaOH is a strong base, not an acid. H₂CO₃ is a weak acid.
Q2What is the pH of a neutral solution at 25°C?
A neutral solution has a pH of 7 at 25°C. pH < 7 indicates an acidic solution, and pH > 7 indicates a basic (alkaline) solution. Pure water has a pH of 7.
Q3What happens when an acid reacts with a metal carbonate? Write a general equation.
When an acid reacts with a metal carbonate, it forms a salt, water, and carbon dioxide gas. General equation: Metal carbonate + Acid → Salt + Water + Carbon dioxide. Example: Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂↑. The CO₂ gas evolved turns lime water milky.
Q4Why does an aqueous solution of an acid conduct electricity?
An aqueous solution of an acid conducts electricity because acids dissociate in water to produce hydrogen ions (H⁺) or hydronium ions (H₃O⁺). These ions act as charge carriers and allow the flow of electric current through the solution. For example, HCl → H⁺ + Cl⁻ in water.
Q5Name the acid present in the following: (a) Vinegar (b) Curd (c) Lemon (d) Ant sting
(a) Vinegar contains acetic acid (CH₃COOH). (b) Curd contains lactic acid. (c) Lemon contains citric acid. (d) Ant sting contains formic acid (methanoic acid).
Practice Acids, Bases and Salts
Reinforce what you just revised with practice questions