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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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Age band:Ages 13-15Ages 16-18

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Worksheet StudioPractice pack · Ages 13-15

Acids, bases & the pH scale

Take your time. Show your thinking.

  1. 1. Why do farmers sometimes spread powdered calcium carbonate (limestone) or calcium oxide on fields: to neutralise overly acidic soil, or to make the soil more acidic?

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

  2. 2. Which gas is produced when a reactive metal (such as magnesium or zinc) reacts with dilute hydrochloric acid: hydrogen or oxygen?

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

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

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

  5. 5. 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

  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 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

  8. 8. 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

  9. 9. 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

  10. 10. 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

  11. 11. 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

  12. 12. 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
12 questions · Seed 51 · 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. 1. Why do farmers sometimes spread powdered calcium carbonate (limestone) or calcium oxide on fields: to neutralise overly acidic soil, or to make the soil more acidic?

    To neutralise overly acidic soil

    Basic calcium compounds neutralise excess soil acidity so crops can grow well.

  2. 2. Which gas is produced when a reactive metal (such as magnesium or zinc) reacts with dilute hydrochloric acid: hydrogen or oxygen?

    Hydrogen

    Metal + Acid → Salt + Hydrogen gas (which gives a squeaky pop with a lighted splint).

  3. 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. 4. 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.

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

    Blue

    Alkalis turn red litmus paper blue.

  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 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.

  8. 8. 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.

  9. 9. 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.

  10. 10. What colour does blue litmus paper turn when dipped into an acidic solution: red or blue?

    Red

    Acids turn blue litmus paper red.

  11. 11. 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.

  12. 12. 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.

12 questions · Seed 51 · Age guidance, not curriculum certification
Worksheet StudioPractice pack · Ages 13-15

Acids, bases & the pH scale

Take your time. Show your thinking.

  1. 1. Why do farmers sometimes spread powdered calcium carbonate (limestone) or calcium oxide on fields: to neutralise overly acidic soil, or to make the soil more acidic?

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

  2. 2. Which gas is produced when a reactive metal (such as magnesium or zinc) reacts with dilute hydrochloric acid: hydrogen or oxygen?

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

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

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

  5. 5. 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

  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 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

  8. 8. 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

  9. 9. 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

  10. 10. 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

  11. 11. 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

  12. 12. 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
12 questions · Seed 51 · Age guidance, not curriculum certification
Worksheet StudioAnswer key · Ages 13-15

Acids, bases & the pH scale

Answers and reasoning. Review before teaching.

  1. 1. Why do farmers sometimes spread powdered calcium carbonate (limestone) or calcium oxide on fields: to neutralise overly acidic soil, or to make the soil more acidic?

    To neutralise overly acidic soil

    Basic calcium compounds neutralise excess soil acidity so crops can grow well.

  2. 2. Which gas is produced when a reactive metal (such as magnesium or zinc) reacts with dilute hydrochloric acid: hydrogen or oxygen?

    Hydrogen

    Metal + Acid → Salt + Hydrogen gas (which gives a squeaky pop with a lighted splint).

  3. 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. 4. 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.

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

    Blue

    Alkalis turn red litmus paper blue.

  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 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.

  8. 8. 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.

  9. 9. 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.

  10. 10. What colour does blue litmus paper turn when dipped into an acidic solution: red or blue?

    Red

    Acids turn blue litmus paper red.

  11. 11. 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.

  12. 12. 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.

12 questions · Seed 51 · Age guidance, not curriculum certification