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S2 Science: Acids, Alkalis and Neutralisation (Paper 3 (challenge))
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S2 Science: Acids, Alkalis and Neutralisation (Paper 3 (challenge))
This paper puts calculation and explanation side by side: moles, dilution, back calculation from titration and the heat released, each with steps and units.
Direct answers Write the equation to fix the mole ratio before substituting numbers, then check units and significant figures, since a wrong unit loses the whole mark. The challenge is not arithmetic but choosing the right formula, so a moment of thought beats rushed working.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 |
| Suggested time | 20 |
| Difficulty mix | Foundation 3 · Intermediate 3 · Challenge 3 · Error redo 1 |
| Chapter | Chapter: S2 Science: Acids, Alkalis and Neutralisation |
| Level | S2 |
02 Questions (10 items)
- FoundationWhat is the correct way to dilute concentrated sulphuric acid?
- FoundationWhich has the lower pH, 0.10 mol/dm³ hydrochloric acid or the same concentration of ethanoic acid?
- FoundationA sodium hydroxide solution contains 4.0 g/dm³. What is its concentration in mol/dm³?
- Intermediate1.2 g of magnesium reacts with excess dilute hydrochloric acid. How many moles of hydrogen are produced?
- IntermediateGiven a molar gas volume of 24 dm³ at room temperature, what volume of hydrogen is produced?
- IntermediateHow many times greater is the hydrogen ion concentration at pH 2 than at pH 6?
- Challenge50.0 cm³ of 1.5 mol/dm³ hydrochloric acid is diluted to 250 cm³. What is the new concentration?
- ChallengeIn a neutralisation, 50 g of solution warms by 6.5 °C and the specific heat capacity is 4.2 J/(g °C). How much energy is released?
- Challenge25.0 cm³ of 0.10 mol/dm³ sodium hydroxide needs 22.5 cm³ of acid. What is the acid concentration?
- Error redoA student thinks neutralisation does not release heat so the temperature stays the same. What is wrong?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | Add the acid slowly to the water while stirring | Diluting concentrated sulphuric acid releases much heat, so water added to acid can spit; always add acid to water. |
| 2 | Hydrochloric acid, because it is fully ionised | A strong acid ionises completely and gives a higher hydrogen ion concentration, while ethanoic acid ionises only partly. |
| 3 | 0.10 mol/dm³ | Divide the mass concentration by the relative formula mass, 4.0 over 40, giving 0.10 mol/dm³. |
| 4 | 0.05 mol | Magnesium has a relative atomic mass of 24, so 1.2 over 24 is 0.05 mol, and the ratio is one to one. |
| 5 | 1.2 dm³ | Volume equals moles times molar volume, so 0.05 times 24 gives 1.2 dm³. |
| 6 | Ten thousand times | Four pH units apart means ten to the power four, that is ten thousand times. |
| 7 | 0.30 mol/dm³ | The moles are 1.5 times 50.0 over 1 000, that is 0.075 mol, and dividing by 0.25 dm³ gives 0.30 mol/dm³. |
| 8 | 1 365 J, about 1.37 kJ | Energy equals mass times specific heat capacity times temperature rise, so 50 times 4.2 times 6.5 is 1 365 J. |
| 9 | About 0.11 mol/dm³ | The alkali gives 0.0025 mol, and dividing by 0.0225 dm³ gives about 0.11 mol/dm³. |
| 10 | Neutralisation releases heat, so the temperature rises | Energy is released when hydrogen and hydroxide ions form water, so the temperature clearly rises. |
04 What to do after marking
- After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
- Repeat the same item two days later; move to the next paper only when both attempts are correct.
- Parents only need the answer and note columns; there is no need to explain every item.
For acid and alkali questions ask three things: is the solution acidic or alkaline, what colour was the indicator, and what is the mole ratio in the neutralisation.Tutor Registration →
Questions and answers are written originally by the TutorZone team and are not taken from any school, publisher or examination authority paper. Every value is checked by computer.