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. 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. 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
3. 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
4. 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
5. 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
6. 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
7. 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
8. 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
9. 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
10. 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
11. What weak organic acid gives vinegar its sour taste: ethanoic (acetic) acid or nitric acid?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
12. 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

12 questions · Seed 104735 · 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. 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. What weak organic acid is found naturally in lemons, limes and oranges: citric acid or sulfuric acid?
Citric acid
Citrus fruits contain citric acid.
3. 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.
4. What colour does blue litmus paper turn when dipped into an acidic solution: red or blue?
Red
Acids turn blue litmus paper red.
5. 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.
6. 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).
7. 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.
8. 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).
9. 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.
10. 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⁺].
11. 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.
12. 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).

12 questions · Seed 104735 · Age guidance, not curriculum certification

Worksheet StudioPractice pack · Ages 16-18

Acids, bases & the pH scale

Take your time. Show your thinking.

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. 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
3. 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
4. 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
5. 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
6. 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
7. 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
8. 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
9. 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
10. 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
11. What weak organic acid gives vinegar its sour taste: ethanoic (acetic) acid or nitric acid?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
12. 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

12 questions · Seed 104735 · Age guidance, not curriculum certification

Worksheet StudioAnswer key · Ages 16-18

Acids, bases & the pH scale

Answers and reasoning. Review before teaching.

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. What weak organic acid is found naturally in lemons, limes and oranges: citric acid or sulfuric acid?
Citric acid
Citrus fruits contain citric acid.
3. 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.
4. What colour does blue litmus paper turn when dipped into an acidic solution: red or blue?
Red
Acids turn blue litmus paper red.
5. 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.
6. 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).
7. 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.
8. 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).
9. 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.
10. 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⁺].
11. 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.
12. 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).

12 questions · Seed 104735 · Age guidance, not curriculum certification