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 13-15 Ages 16-18

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Worksheet StudioPractice pack · Ages 13-15

Acids, bases & the pH scale

Take your time. Show your thinking.

1. 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
2. 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
3. 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
4. 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
5. 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
6. 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
7. Which salt is formed when hydrochloric acid (HCl) is neutralised by sodium hydroxide (NaOH): sodium chloride or sodium sulfate?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
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. 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. 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
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. 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

12 questions · Seed 45 · 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. 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.
2. 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).
3. 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).
4. 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⁻).
5. 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.
6. What weak organic acid is found naturally in lemons, limes and oranges: citric acid or sulfuric acid?
Citric acid
Citrus fruits contain citric acid.
7. Which salt is formed when hydrochloric acid (HCl) is neutralised by sodium hydroxide (NaOH): sodium chloride or sodium sulfate?
Sodium chloride
HCl + NaOH → NaCl (sodium chloride) + H₂O.
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. 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. 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.
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. What colour does blue litmus paper turn when dipped into an acidic solution: red or blue?
Red
Acids turn blue litmus paper red.

12 questions · Seed 45 · Age guidance, not curriculum certification

Worksheet StudioPractice pack · Ages 13-15

Acids, bases & the pH scale

Take your time. Show your thinking.

1. 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
2. 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
3. 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
4. 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
5. 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
6. 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
7. Which salt is formed when hydrochloric acid (HCl) is neutralised by sodium hydroxide (NaOH): sodium chloride or sodium sulfate?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
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. 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. 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
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. 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

12 questions · Seed 45 · Age guidance, not curriculum certification

Worksheet StudioAnswer key · Ages 13-15

Acids, bases & the pH scale

Answers and reasoning. Review before teaching.

1. 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.
2. 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).
3. 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).
4. 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⁻).
5. 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.
6. What weak organic acid is found naturally in lemons, limes and oranges: citric acid or sulfuric acid?
Citric acid
Citrus fruits contain citric acid.
7. Which salt is formed when hydrochloric acid (HCl) is neutralised by sodium hydroxide (NaOH): sodium chloride or sodium sulfate?
Sodium chloride
HCl + NaOH → NaCl (sodium chloride) + H₂O.
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. 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. 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.
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. What colour does blue litmus paper turn when dipped into an acidic solution: red or blue?
Red
Acids turn blue litmus paper red.

12 questions · Seed 45 · Age guidance, not curriculum certification