中文（繁體）
中文（简体）
English
S2 Science: Acids, Alkalis and Neutralisation (Paper 4 (error clinic))
← Back to the Secondary Science chapter index
S2 Science: Acids, Alkalis and Neutralisation (Paper 4 (error clinic))
This paper targets the usual errors: the direction of indicator colours, how pH moves on dilution, mole and volume conversion, and laboratory safety.
Direct answers Write the formula before substituting numbers, keep units, and divide by 1 000 as soon as a question asks for moles. Only four colour combinations need memorising, and most confusion comes from swapping litmus with phenolphthalein.
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)
- FoundationLitmus turning from red to blue shows the solution is what?
- FoundationOver what pH range do common acid base indicators work?
- FoundationWhat two kinds of substance are formed when an acid is neutralised by an alkali?
- IntermediateWhat colour is phenolphthalein in sodium hydroxide solution?
- IntermediateAn acidic solution is diluted ten times. By how much does the pH rise?
- IntermediateWhat gas is released when an acid reacts with a carbonate?
- Challenge0.05 mol of hydrogen chloride is dissolved to make 250 cm³ of solution. What is the concentration?
- Challenge20.0 cm³ of 0.25 mol/dm³ sodium hydroxide is neutralised by acid of the same concentration. What volume is needed?
- ChallengeHow many moles of hydrogen chloride are in 25.0 cm³ of 0.10 mol/dm³ hydrochloric acid?
- Error redoA student thinks laboratory acids can be identified by tasting them. What is wrong?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | Alkaline | Red to blue means alkaline, while blue to red means acidic. |
| 2 | From 0 to 14 | The pH scale runs from 0 to 14, with 7 neutral and the two ends strongly acidic and strongly alkaline. |
| 3 | A salt and water | Hydrogen ions from the acid join hydroxide ions from the alkali to form water, and the rest makes the salt. |
| 4 | Pink | Phenolphthalein turns pink in alkali and stays colourless in acid or neutral solutions. |
| 5 | By about 1 | Ten times fewer hydrogen ions raises the pH by 1, and it never goes above 7. |
| 6 | Carbon dioxide | The carbon dioxide turns limewater milky, which is the usual test for a carbonate. |
| 7 | 0.20 mol/dm³ | Concentration is moles divided by volume, so 0.05 over 0.25 gives 0.20 mol/dm³. |
| 8 | 20.0 cm³ | The ratio is one to one and the concentrations are equal, so the volumes are equal. |
| 9 | 0.0025 mol | Moles equal concentration times volume, so 0.10 times 25.0 divided by 1 000 gives 0.0025 mol. |
| 10 | Laboratory acids are corrosive and must be tested with indicators, never tasted | Concentrated acids badly burn the mouth and throat, and no chemical in a laboratory is ever tasted. |
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.