ScienceAges 13-15

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.

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Worksheet StudioPractice pack · Ages 13-15

Acids, bases & the pH scale

Take your time. Show your thinking.

1. 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
2. What colour does red litmus paper turn when dipped into an alkaline solution: blue or yellow?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
3. What colour does Universal Indicator turn in a neutral solution of pH 7: green or red?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
4. 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
5. 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
6. What is the chemical test that confirms a gas is carbon dioxide (CO₂): it turns clear limewater cloudy (milky), or it relights a glowing splint?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
7. 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
8. 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
9. 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
10. Which gas is produced when a metal carbonate (such as calcium carbonate) reacts with an acid: carbon dioxide or nitrogen?
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 type of salt is always produced by reactions of sulfuric acid (H₂SO₄): a sulfate or a nitrate?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution

12 questions · Seed 55 · Age guidance, not curriculum certification

View the answer key

Worksheet StudioAnswer key · Ages 13-15

Acids, bases & the pH scale

Answers and reasoning. Review before teaching.

1. 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.
2. What colour does red litmus paper turn when dipped into an alkaline solution: blue or yellow?
Blue
Alkalis turn red litmus paper blue.
3. What colour does Universal Indicator turn in a neutral solution of pH 7: green or red?
Green
Universal Indicator is green at neutral pH 7, red in strong acid, and purple in strong alkali.
4. 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).
5. What colour does blue litmus paper turn when dipped into an acidic solution: red or blue?
Red
Acids turn blue litmus paper red.
6. What is the chemical test that confirms a gas is carbon dioxide (CO₂): it turns clear limewater cloudy (milky), or it relights a glowing splint?
It turns clear limewater cloudy (milky)
CO₂ reacts with calcium hydroxide (limewater) to form an insoluble white precipitate of calcium carbonate.
7. 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.
8. 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.
9. 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⁺].
10. Which gas is produced when a metal carbonate (such as calcium carbonate) reacts with an acid: carbon dioxide or nitrogen?
Carbon dioxide
Acid + Carbonate → Salt + Water + Carbon dioxide (which turns limewater milky).
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 type of salt is always produced by reactions of sulfuric acid (H₂SO₄): a sulfate or a nitrate?
Sulfate
Sulfuric acid forms sulfate salts; nitric acid forms nitrates; hydrochloric acid forms chlorides.

12 questions · Seed 55 · Age guidance, not curriculum certification

Worksheet StudioPractice pack · Ages 13-15

Acids, bases & the pH scale

Take your time. Show your thinking.

1. 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
2. What colour does red litmus paper turn when dipped into an alkaline solution: blue or yellow?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
3. What colour does Universal Indicator turn in a neutral solution of pH 7: green or red?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
4. 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
5. 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
6. What is the chemical test that confirms a gas is carbon dioxide (CO₂): it turns clear limewater cloudy (milky), or it relights a glowing splint?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
7. 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
8. 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
9. 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
10. Which gas is produced when a metal carbonate (such as calcium carbonate) reacts with an acid: carbon dioxide or nitrogen?
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 type of salt is always produced by reactions of sulfuric acid (H₂SO₄): a sulfate or a nitrate?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution

12 questions · Seed 55 · Age guidance, not curriculum certification

Worksheet StudioAnswer key · Ages 13-15

Acids, bases & the pH scale

Answers and reasoning. Review before teaching.

1. 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.
2. What colour does red litmus paper turn when dipped into an alkaline solution: blue or yellow?
Blue
Alkalis turn red litmus paper blue.
3. What colour does Universal Indicator turn in a neutral solution of pH 7: green or red?
Green
Universal Indicator is green at neutral pH 7, red in strong acid, and purple in strong alkali.
4. 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).
5. What colour does blue litmus paper turn when dipped into an acidic solution: red or blue?
Red
Acids turn blue litmus paper red.
6. What is the chemical test that confirms a gas is carbon dioxide (CO₂): it turns clear limewater cloudy (milky), or it relights a glowing splint?
It turns clear limewater cloudy (milky)
CO₂ reacts with calcium hydroxide (limewater) to form an insoluble white precipitate of calcium carbonate.
7. 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.
8. 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.
9. 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⁺].
10. Which gas is produced when a metal carbonate (such as calcium carbonate) reacts with an acid: carbon dioxide or nitrogen?
Carbon dioxide
Acid + Carbonate → Salt + Water + Carbon dioxide (which turns limewater milky).
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 type of salt is always produced by reactions of sulfuric acid (H₂SO₄): a sulfate or a nitrate?
Sulfate
Sulfuric acid forms sulfate salts; nitric acid forms nitrates; hydrochloric acid forms chlorides.

12 questions · Seed 55 · Age guidance, not curriculum certification