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. 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
2. 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
3. Does an alkaline (basic) solution (such as sodium hydroxide or soapy water) have a pH greater than 7 or less than 7?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
4. 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
5. What is the difference between a strong acid (like HCl) and a weak acid (like ethanoic acid) in water: a strong acid fully ionises (dissociates), whereas a weak acid only partially ionises, or a strong acid has pH 12?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
6. 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
7. 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
8. What weak organic acid gives vinegar its sour taste: ethanoic (acetic) acid or nitric acid?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
9. What weak organic acid is found naturally in lemons, limes and oranges: citric acid or sulfuric acid?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
10. 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
11. 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
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 42 · 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. 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.
2. 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⁻).
3. Does an alkaline (basic) solution (such as sodium hydroxide or soapy water) have a pH greater than 7 or less than 7?
Greater than 7
Alkalis (soluble bases) have pH values above 7 (from 7 to 14).
4. 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.
5. What is the difference between a strong acid (like HCl) and a weak acid (like ethanoic acid) in water: a strong acid fully ionises (dissociates), whereas a weak acid only partially ionises, or a strong acid has pH 12?
A strong acid fully ionises (dissociates), whereas a weak acid only partially ionises
Acid strength refers to the degree of ionisation in water.
6. 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.
7. 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.
8. 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.
9. What weak organic acid is found naturally in lemons, limes and oranges: citric acid or sulfuric acid?
Citric acid
Citrus fruits contain citric acid.
10. What colour does red litmus paper turn when dipped into an alkaline solution: blue or yellow?
Blue
Alkalis turn red litmus paper blue.
11. 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.
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 42 · Age guidance, not curriculum certification

Worksheet StudioPractice pack · Ages 13-15

Acids, bases & the pH scale

Take your time. Show your thinking.

1. 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
2. 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
3. Does an alkaline (basic) solution (such as sodium hydroxide or soapy water) have a pH greater than 7 or less than 7?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
4. 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
5. What is the difference between a strong acid (like HCl) and a weak acid (like ethanoic acid) in water: a strong acid fully ionises (dissociates), whereas a weak acid only partially ionises, or a strong acid has pH 12?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
6. 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
7. 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
8. What weak organic acid gives vinegar its sour taste: ethanoic (acetic) acid or nitric acid?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
9. What weak organic acid is found naturally in lemons, limes and oranges: citric acid or sulfuric acid?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
10. 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
11. 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
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 42 · Age guidance, not curriculum certification

Worksheet StudioAnswer key · Ages 13-15

Acids, bases & the pH scale

Answers and reasoning. Review before teaching.

1. 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.
2. 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⁻).
3. Does an alkaline (basic) solution (such as sodium hydroxide or soapy water) have a pH greater than 7 or less than 7?
Greater than 7
Alkalis (soluble bases) have pH values above 7 (from 7 to 14).
4. 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.
5. What is the difference between a strong acid (like HCl) and a weak acid (like ethanoic acid) in water: a strong acid fully ionises (dissociates), whereas a weak acid only partially ionises, or a strong acid has pH 12?
A strong acid fully ionises (dissociates), whereas a weak acid only partially ionises
Acid strength refers to the degree of ionisation in water.
6. 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.
7. 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.
8. 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.
9. What weak organic acid is found naturally in lemons, limes and oranges: citric acid or sulfuric acid?
Citric acid
Citrus fruits contain citric acid.
10. What colour does red litmus paper turn when dipped into an alkaline solution: blue or yellow?
Blue
Alkalis turn red litmus paper blue.
11. 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.
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 42 · Age guidance, not curriculum certification