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S2 Science: Acids, Alkalis and Neutralisation (Paper 2 (intermediate))
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S2 Science: Acids, Alkalis and Neutralisation (Paper 2 (intermediate))
This paper links indicator colours, dilution calculations, the heat of neutralisation and averaging titrations, and every value needs a unit.
Direct answers Write the number of moles first, then divide by the new volume; forgetting to divide by 1 000 is the most common lost mark. Only convert cm³ to dm³ while finding moles, and give the final answer back in cm³.
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 colours does methyl orange show in acidic and in alkaline solutions?
- FoundationWhat gas is released when dilute hydrochloric acid is added to calcium carbonate?
- FoundationA solution has a pH of 9. Is it acidic, neutral or alkaline?
- Intermediate20 cm³ of 2.0 mol/dm³ hydrochloric acid is diluted to 200 cm³. What is the new concentration?
- IntermediateIn a neutralisation experiment the temperature rises from 24.5 °C to 30.5 °C. What is the rise?
- IntermediateUsing phenolphthalein, sodium hydroxide is added to hydrochloric acid. How does the colour change at the end point?
- ChallengeHow many moles of sodium hydroxide neutralise 25.0 cm³ of 0.20 mol/dm³ hydrochloric acid?
- ChallengeGiven a relative formula mass of 40 for sodium hydroxide, what mass is needed?
- ChallengeThree titrations use 19.8 cm³, 20.0 cm³ and 19.9 cm³. What is the average volume?
- Error redoA student thinks diluting an acid lowers its pH. What is wrong?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | Red in acid and yellow in alkali | Methyl orange is red below pH 3.1 and yellow above pH 4.4, with orange in between. |
| 2 | Carbon dioxide, which turns limewater milky | An acid with a carbonate gives carbon dioxide, the usual test for a carbonate. |
| 3 | Alkaline, and only weakly so | A value above 7 is alkaline, and only two units above neutral means a weak alkali. |
| 4 | 0.20 mol/dm³ | The number of moles stays the same, so 2.0 times 20 divided by 200 gives 0.20. |
| 5 | 6.0 °C | 30.5 minus 24.5 is 6.0, and the rise shows that neutralisation releases heat. |
| 6 | From colourless to pink, and the pink lasts for half a minute | The solution only turns pink once it becomes alkaline, so the colour must persist. |
| 7 | 0.005 mol | Moles equal concentration times volume, so 0.20 times 25.0 divided by 1 000 gives 0.005. |
| 8 | 0.20 g | Mass equals moles times relative formula mass, so 0.005 times 40 gives 0.20 g. |
| 9 | 19.9 cm³ | The three readings add to 59.7, and dividing by 3 gives 19.9 cm³. |
| 10 | Dilution weakens the acid, so the pH rises towards 7 | Dilution lowers the hydrogen ion concentration, so the pH increases but never passes 7. |
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.