中文（繁體）
中文（简体）
English
S5 Chemistry: Electrolysis – Faraday Calculations (Paper 2: Intermediate)
S5 Chemistry: Electrolysis – Faraday Calculations (Paper 2: Intermediate)
Ten items converting charge into moles and mass, with the key design points of aluminium and chlor-alkali plants.
Direct answers Answers in order: copper deposits, 6000 C, bromine, 0.10 mol, 15.9 g, it lowers the melting point, 0.373 mol, 3.6 g, hypochlorite forms, 0.10 mol.
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: S5 Chemistry: Electrolysis and Industrial Applications |
| Level | S5 |
02 Questions (10 items)
- FoundationCopper electrodes are used in copper sulphate solution. What forms at the cathode?
- FoundationA current of 4.0 A flows for 25 minutes. What charge passes?
- FoundationWhat is produced at the anode when molten lead bromide is electrolysed?
- Intermediate19300 C passes through dilute sulphuric acid. How many moles of hydrogen form at the cathode?
- IntermediateA copper sulphate solution passes 0.50 mol of electrons. What mass of copper deposits? (Cu = 63.5)
- IntermediateCryolite is added when extracting aluminium from alumina. What is its purpose?
- ChallengeA current of 5.0 A flows for 2 hours. How many moles of electrons pass?
- ChallengeA current of 3.0 A runs for one hour with a copper anode. What mass of copper dissolves?
- ChallengeWhy must chlorine be kept away from sodium hydroxide in the chlor-alkali process?
- Error redoError replay: a student claims 0.20 mol of electrons deposits 0.20 mol of copper. What is correct?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | Copper is deposited on the cathode | Copper ions are reduced and the metal settles on the electrode. |
| 2 | 6000 C | Twenty five minutes is 1500 seconds, and multiplying by 4.0 A gives 6000 C. |
| 3 | Bromine | Bromide ions lose electrons at the anode and bromine molecules form. |
| 4 | 0.10 mol | That is 0.20 mol of electrons, and each hydrogen molecule needs two, so 0.10 mol forms. |
| 5 | 15.9 g | Each copper ion needs two electrons, giving 0.25 mol of copper, which is about 15.9 g. |
| 6 | It lowers the melting point of alumina and saves energy | Cryolite brings the melting point from about two thousand degrees down to about one thousand. |
| 7 | 0.373 mol | The charge is 36000 C, and dividing by 96500 gives 0.373 mol. |
| 8 | 3.6 g | The charge of 10800 C gives about 0.112 mol of electrons, so 0.056 mol of copper dissolves. |
| 9 | They react to form sodium hypochlorite and the products lose purity | Chlorine in alkali forms hypochlorite, so a diaphragm keeps the two electrode products apart. |
| 10 | 0.10 mol | Copper ions carry two charges, so two electrons are needed for each ion and the amount halves. |
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.
Confirm the number of electrons first, then multiply moles by molar mass.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.