Chemistry · Both
Acids, Alkalis & Salts
The pH scale, acids and alkalis, indicators, neutralisation and making salts.
Acids and alkalis are common in the lab and in everyday life. Know the pH scale, neutralisation, and how salts are formed.
pH scale
pH measures how acidic or alkaline a solution is (usually 0–14).
• pH < 7 → **acidic**
• pH = 7 → **neutral**
• pH > 7 → **alkaline**
Strong acids: low pH (e.g. 0–1). Strong alkalis: high pH (e.g. 13–14).
Indicators (e.g. universal indicator, litmus) change colour with pH.
Neutralisation
Acid + alkali → **salt + water**
Examples:
• Hydrochloric acid + sodium hydroxide → sodium chloride + water
• Sulfuric acid + potassium hydroxide → potassium sulfate + water
H⁺ (from acid) + OH⁻ (from alkali) → H₂O
Worked example
Name the salt formed when hydrochloric acid reacts with potassium hydroxide.
Solution
**Potassium chloride** (and water).
Common acids and alkalis
**Acids:** hydrochloric (HCl), sulfuric (H₂SO₄), nitric (HNO₃), ethanoic (vinegar)
**Alkalis:** sodium hydroxide (NaOH), potassium hydroxide (KOH), ammonia solution
Bases are substances that neutralise acids; alkalis are bases that dissolve in water.
Practice questions
Try these without looking at the answers first.
Q1.Is pH 3 acidic, neutral or alkaline?
Show answer
Acidic
Q2.Acid + alkali → ?
Show answer
Salt + water
Q3.What ions make a solution acidic?
Show answer
H⁺ (hydrogen ions)