ScienceAges 16-18

Acids, bases & the pH scale

Use the 0–14 pH scale, indicators and neutralisation reactions to classify acidic, neutral and alkaline solutions. Review suitability for your learners before teaching.

New variation Try interactive challenge Browse templates

Age band:Ages 13-15 Ages 16-18

Choose “Save as PDF” to keep a copy. Use your browser’s paper setting for A4 or Letter.

Worksheet StudioPractice pack · Ages 16-18

Acids, bases & the pH scale

Take your time. Show your thinking.

1. What weak organic acid gives vinegar its sour taste: ethanoic (acetic) acid or nitric acid?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
2. On the standard pH scale (0 to 14) at 25 °C, what is the pH of a neutral solution such as pure water: 7 or 0?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
3. Does an acidic solution (such as lemon juice or hydrochloric acid) have a pH less than 7 or greater than 7?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
4. Which ion is present in all aqueous alkaline solutions: hydroxide ions (OH⁻) or chloride ions (Cl⁻)?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
5. Why do indigestion tablets (antacids) contain mild bases such as magnesium hydroxide or calcium carbonate: to neutralise excess stomach acid, or to add more acid?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
6. Because the pH scale is logarithmic, a decrease of 1 pH unit (e.g. from pH 4 to pH 3) means the H⁺ ion concentration increases by a factor of: 10 or 2?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
7. What colour does blue litmus paper turn when dipped into an acidic solution: red or blue?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
8. Which salt is formed when hydrochloric acid (HCl) is neutralised by sodium hydroxide (NaOH): sodium chloride or sodium sulfate?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
9. Which ion is released by all Arrhenius acids when dissolved in aqueous solution: hydrogen ions (H⁺) or hydroxide ions (OH⁻)?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
10. What are the two products formed when an acid reacts with an alkali in a neutralisation reaction: a salt and water, or hydrogen and carbon?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
11. What is the chemical test that confirms a gas is oxygen (O₂): it relights a glowing wooden splint, or it turns limewater milky?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
12. Which solution is more strongly acidic: Solution A with pH 1, or Solution B with pH 5?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution

12 questions · Seed 104746 · Age guidance, not curriculum certification

View the answer key

Worksheet StudioAnswer key · Ages 16-18

Acids, bases & the pH scale

Answers and reasoning. Review before teaching.

1. What weak organic acid gives vinegar its sour taste: ethanoic (acetic) acid or nitric acid?
Ethanoic (acetic) acid
Vinegar is a dilute aqueous solution of ethanoic (acetic) acid.
2. On the standard pH scale (0 to 14) at 25 °C, what is the pH of a neutral solution such as pure water: 7 or 0?
7
A pH of 7 is neutral, with equal concentrations of H⁺ and OH⁻ ions.
3. Does an acidic solution (such as lemon juice or hydrochloric acid) have a pH less than 7 or greater than 7?
Less than 7
Acids have pH values below 7; the lower the pH, the stronger or more concentrated the acid.
4. Which ion is present in all aqueous alkaline solutions: hydroxide ions (OH⁻) or chloride ions (Cl⁻)?
Hydroxide ions (OH⁻)
Alkalis dissolve in water to release hydroxide ions (OH⁻).
5. Why do indigestion tablets (antacids) contain mild bases such as magnesium hydroxide or calcium carbonate: to neutralise excess stomach acid, or to add more acid?
To neutralise excess stomach acid
Antacids are weak bases that neutralise excess hydrochloric acid in the stomach.
6. Because the pH scale is logarithmic, a decrease of 1 pH unit (e.g. from pH 4 to pH 3) means the H⁺ ion concentration increases by a factor of: 10 or 2?
10
pH = −log₁₀[H⁺], so each whole unit decrease represents a tenfold increase in [H⁺].
7. What colour does blue litmus paper turn when dipped into an acidic solution: red or blue?
Red
Acids turn blue litmus paper red.
8. Which salt is formed when hydrochloric acid (HCl) is neutralised by sodium hydroxide (NaOH): sodium chloride or sodium sulfate?
Sodium chloride
HCl + NaOH → NaCl (sodium chloride) + H₂O.
9. Which ion is released by all Arrhenius acids when dissolved in aqueous solution: hydrogen ions (H⁺) or hydroxide ions (OH⁻)?
Hydrogen ions (H⁺)
Acids produce aqueous hydrogen ions (H⁺ / H₃O⁺) in water.
10. What are the two products formed when an acid reacts with an alkali in a neutralisation reaction: a salt and water, or hydrogen and carbon?
A salt and water
Acid + Alkali → Salt + Water (H⁺ + OH⁻ → H₂O).
11. What is the chemical test that confirms a gas is oxygen (O₂): it relights a glowing wooden splint, or it turns limewater milky?
It relights a glowing wooden splint
Pure oxygen supports rapid combustion and relights a glowing splint.
12. Which solution is more strongly acidic: Solution A with pH 1, or Solution B with pH 5?
Solution A with pH 1
Lower numbers on the pH scale indicate higher hydrogen-ion concentration and stronger acidity.

12 questions · Seed 104746 · Age guidance, not curriculum certification

Worksheet StudioPractice pack · Ages 16-18

Acids, bases & the pH scale

Take your time. Show your thinking.

1. What weak organic acid gives vinegar its sour taste: ethanoic (acetic) acid or nitric acid?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
2. On the standard pH scale (0 to 14) at 25 °C, what is the pH of a neutral solution such as pure water: 7 or 0?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
3. Does an acidic solution (such as lemon juice or hydrochloric acid) have a pH less than 7 or greater than 7?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
4. Which ion is present in all aqueous alkaline solutions: hydroxide ions (OH⁻) or chloride ions (Cl⁻)?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
5. Why do indigestion tablets (antacids) contain mild bases such as magnesium hydroxide or calcium carbonate: to neutralise excess stomach acid, or to add more acid?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
6. Because the pH scale is logarithmic, a decrease of 1 pH unit (e.g. from pH 4 to pH 3) means the H⁺ ion concentration increases by a factor of: 10 or 2?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
7. What colour does blue litmus paper turn when dipped into an acidic solution: red or blue?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
8. Which salt is formed when hydrochloric acid (HCl) is neutralised by sodium hydroxide (NaOH): sodium chloride or sodium sulfate?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
9. Which ion is released by all Arrhenius acids when dissolved in aqueous solution: hydrogen ions (H⁺) or hydroxide ions (OH⁻)?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
10. What are the two products formed when an acid reacts with an alkali in a neutralisation reaction: a salt and water, or hydrogen and carbon?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
11. What is the chemical test that confirms a gas is oxygen (O₂): it relights a glowing wooden splint, or it turns limewater milky?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
12. Which solution is more strongly acidic: Solution A with pH 1, or Solution B with pH 5?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution

12 questions · Seed 104746 · Age guidance, not curriculum certification

Worksheet StudioAnswer key · Ages 16-18

Acids, bases & the pH scale

Answers and reasoning. Review before teaching.

1. What weak organic acid gives vinegar its sour taste: ethanoic (acetic) acid or nitric acid?
Ethanoic (acetic) acid
Vinegar is a dilute aqueous solution of ethanoic (acetic) acid.
2. On the standard pH scale (0 to 14) at 25 °C, what is the pH of a neutral solution such as pure water: 7 or 0?
7
A pH of 7 is neutral, with equal concentrations of H⁺ and OH⁻ ions.
3. Does an acidic solution (such as lemon juice or hydrochloric acid) have a pH less than 7 or greater than 7?
Less than 7
Acids have pH values below 7; the lower the pH, the stronger or more concentrated the acid.
4. Which ion is present in all aqueous alkaline solutions: hydroxide ions (OH⁻) or chloride ions (Cl⁻)?
Hydroxide ions (OH⁻)
Alkalis dissolve in water to release hydroxide ions (OH⁻).
5. Why do indigestion tablets (antacids) contain mild bases such as magnesium hydroxide or calcium carbonate: to neutralise excess stomach acid, or to add more acid?
To neutralise excess stomach acid
Antacids are weak bases that neutralise excess hydrochloric acid in the stomach.
6. Because the pH scale is logarithmic, a decrease of 1 pH unit (e.g. from pH 4 to pH 3) means the H⁺ ion concentration increases by a factor of: 10 or 2?
10
pH = −log₁₀[H⁺], so each whole unit decrease represents a tenfold increase in [H⁺].
7. What colour does blue litmus paper turn when dipped into an acidic solution: red or blue?
Red
Acids turn blue litmus paper red.
8. Which salt is formed when hydrochloric acid (HCl) is neutralised by sodium hydroxide (NaOH): sodium chloride or sodium sulfate?
Sodium chloride
HCl + NaOH → NaCl (sodium chloride) + H₂O.
9. Which ion is released by all Arrhenius acids when dissolved in aqueous solution: hydrogen ions (H⁺) or hydroxide ions (OH⁻)?
Hydrogen ions (H⁺)
Acids produce aqueous hydrogen ions (H⁺ / H₃O⁺) in water.
10. What are the two products formed when an acid reacts with an alkali in a neutralisation reaction: a salt and water, or hydrogen and carbon?
A salt and water
Acid + Alkali → Salt + Water (H⁺ + OH⁻ → H₂O).
11. What is the chemical test that confirms a gas is oxygen (O₂): it relights a glowing wooden splint, or it turns limewater milky?
It relights a glowing wooden splint
Pure oxygen supports rapid combustion and relights a glowing splint.
12. Which solution is more strongly acidic: Solution A with pH 1, or Solution B with pH 5?
Solution A with pH 1
Lower numbers on the pH scale indicate higher hydrogen-ion concentration and stronger acidity.

12 questions · Seed 104746 · Age guidance, not curriculum certification