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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.

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Worksheet StudioPractice pack · Ages 16-18

Acids, bases & the pH scale

Take your time. Show your thinking.

  1. 1. 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

  2. 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. 3. What weak organic acid gives vinegar its sour taste: ethanoic (acetic) acid or nitric acid?

    pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution

  4. 4. 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

  5. 5. 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

  6. 6. 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

  7. 7. What colour is phenolphthalein indicator in an acidic solution vs a basic solution: colourless in acid and pink in alkali, or blue in both?

    pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution

  8. 8. 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

  9. 9. In an acid–base titration, which piece of graduated glassware with a tap at the bottom is used to measure the exact volume of acid or alkali added: a burette or a beaker?

    pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution

  10. 10. 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

  11. 11. 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

  12. 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 49 · 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. 1. What colour does red litmus paper turn when dipped into an alkaline solution: blue or yellow?

    Blue

    Alkalis turn red litmus paper blue.

  2. 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. 3. 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.

  4. 4. 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.

  5. 5. 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).

  6. 6. 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.

  7. 7. What colour is phenolphthalein indicator in an acidic solution vs a basic solution: colourless in acid and pink in alkali, or blue in both?

    Colourless in acid and pink in alkali

    Phenolphthalein is colourless below pH 8.2 and turns pink-magenta in alkaline solutions.

  8. 8. 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.

  9. 9. In an acid–base titration, which piece of graduated glassware with a tap at the bottom is used to measure the exact volume of acid or alkali added: a burette or a beaker?

    Burette

    A burette delivers variable volumes accurately to within 0.05 cm³.

  10. 10. What weak organic acid is found naturally in lemons, limes and oranges: citric acid or sulfuric acid?

    Citric acid

    Citrus fruits contain citric acid.

  11. 11. 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.

  12. 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 49 · Age guidance, not curriculum certification
Worksheet StudioPractice pack · Ages 16-18

Acids, bases & the pH scale

Take your time. Show your thinking.

  1. 1. 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

  2. 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. 3. What weak organic acid gives vinegar its sour taste: ethanoic (acetic) acid or nitric acid?

    pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution

  4. 4. 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

  5. 5. 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

  6. 6. 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

  7. 7. What colour is phenolphthalein indicator in an acidic solution vs a basic solution: colourless in acid and pink in alkali, or blue in both?

    pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution

  8. 8. 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

  9. 9. In an acid–base titration, which piece of graduated glassware with a tap at the bottom is used to measure the exact volume of acid or alkali added: a burette or a beaker?

    pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution

  10. 10. 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

  11. 11. 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

  12. 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 49 · Age guidance, not curriculum certification
Worksheet StudioAnswer key · Ages 16-18

Acids, bases & the pH scale

Answers and reasoning. Review before teaching.

  1. 1. What colour does red litmus paper turn when dipped into an alkaline solution: blue or yellow?

    Blue

    Alkalis turn red litmus paper blue.

  2. 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. 3. 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.

  4. 4. 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.

  5. 5. 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).

  6. 6. 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.

  7. 7. What colour is phenolphthalein indicator in an acidic solution vs a basic solution: colourless in acid and pink in alkali, or blue in both?

    Colourless in acid and pink in alkali

    Phenolphthalein is colourless below pH 8.2 and turns pink-magenta in alkaline solutions.

  8. 8. 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.

  9. 9. In an acid–base titration, which piece of graduated glassware with a tap at the bottom is used to measure the exact volume of acid or alkali added: a burette or a beaker?

    Burette

    A burette delivers variable volumes accurately to within 0.05 cm³.

  10. 10. What weak organic acid is found naturally in lemons, limes and oranges: citric acid or sulfuric acid?

    Citric acid

    Citrus fruits contain citric acid.

  11. 11. 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.

  12. 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 49 · Age guidance, not curriculum certification