Practical & Inquiry实验与探究
Think like a chemist. Turn observations into evidence, and evidence into explanations.像化学家一样思考：从观察出发，用证据解释现象。
Choose a skill to explore选择一项技能开始探究
Make an experimental decision做出你的实验判断
Choose an answer, check the explanation and try again when needed.选择答案，检查理由，再根据反馈修正思路。
01 · Choose a measurement选择测量工具
You need to transfer exactly 25.0 cm³ of solution. Which apparatus is most suitable?需要准确转移 25.0 cm³ 溶液，应选择哪种仪器？
02 · Read experimental data读懂实验数据
Gas volume is 18 cm³ at 20 s and 30 cm³ at 40 s. What is the average rate over this interval?20 s 时气体体积为 18 cm³，40 s 时为 30 cm³，这一时间段的平均速率是多少？
03 · Control a variable控制实验变量
To investigate the effect of temperature on reaction rate, which comparison is fair?研究温度对反应速率的影响，哪种比较是公平的？
04 · Evaluate a result评价实验结果
A leaking connection makes the measured gas volume too low. Which improvement addresses this error?装置漏气使测得的气体体积偏低，哪种改进能解决这个问题？
Paper 6 practicePaper 6 专项训练
Use these printable resources alongside the experimental skills below. Try a full paper or practise one section at a time.结合下方技能模块使用可打印资料，可以完成整卷，也可以分项训练。
Guided worksheet
Five modules with teacher models, independent tasks and partner checks.
Download DOCX ↓40 mark practice paper
Original classroom questions. Allow 60 minutes or practise one section at a time.
Download DOCX ↓Hint cards
Paper 6 cards are on pages 7–9. Use them during learning, then try without support.
Download DOCX ↓Apparatus and measurements仪器与测量
Select apparatus, read scales and calculate delivered volumes.
- Paper 6 asks you to use experimental evidence. It is a one-hour, 40-mark alternative-to-practical paper.
- A pipette delivers a fixed accurate volume. A burette delivers a measured variable volume. A measuring cylinder gives less precise volume measurements.
- The scale increases downwards. Read the bottom of a clear solution’s meniscus at eye level.
- A rough titration locates the endpoint. Repeat accurate titrations and use consistent results according to the question’s criterion.
Quick check
Why is the final burette reading alone not always the titre?
Check after attempting
The starting reading may be above zero. The titre is the difference.
Separation and salt preparation分离与盐的制备
Explain a method using the properties of the substances involved.
- Filtration separates an insoluble solid from a liquid. Crystallisation recovers a dissolved solid.
- Warm dilute acid and add the suitable insoluble base in small portions until some solid remains. Filter off the excess.
- Draw the baseline in pencil and keep it above the solvent. Mark the solvent front before it evaporates.
- A gas syringe measures gas volume. Collection over water is suitable only if the gas is sufficiently insoluble and does not react with water.
Quick check
Why can filtration alone not separate dissolved salt from water?
Check after attempting
The dissolved ions pass through the filter with the water.
Observations and qualitative analysis观察与定性分析
Use the supplied analysis notes to select tests and justify identities.
- Write a visible observation: “a light blue precipitate forms”. Then infer an ion by comparing the notes.
- With aqueous ammonia, Cu²⁺ gives a light blue precipitate that dissolves in excess to form a dark blue solution.
- For halides, acidify with dilute nitric acid and add silver nitrate: chloride white, bromide cream, iodide yellow.
- Hydrogen pops with a lighted splint. Oxygen relights a glowing splint. Carbon dioxide turns limewater milky.
Quick check
Why should hydrochloric acid not be used to acidify a chloride test?
Check after attempting
It introduces chloride ions and can cause a misleading positive result.
Tables graphs and evaluation表格、图像与实验评价
Process data, identify anomalous results and link improvements to errors.
- Illustrative data: a fixed mass of magnesium reacts with excess acid. A gas syringe measures hydrogen every 20 s.
- Put time on the horizontal axis and volume on the vertical axis. Label quantities and units and choose an even scale.
- Average rate over an interval = change in volume / change in time. A tangent estimates the rate at an instant.
- A leak loses gas and makes measured volume too low. Check the bung and connections before starting.
Quick check
Will repeating a leaking gas-collection experiment automatically make the result accurate?
Check after attempting
No. Repair the leak. Repeats can reveal variability but do not remove systematic loss.
Planning an investigation设计探究
Write a reproducible plan with variables, measurements and data processing.
- State what you change and what you measure. Give a sensible range and units. Keep relevant quantities constant.
- In a solution model, change one quantity at a time. Distinguish the amount dissolved from how quickly a solid dissolves.
- A suitable classroom planning context is magnesium reacting with excess dilute acid. Compare fixed temperatures using a water bath.
- Specify a hazard and matching precaution: dilute acid can irritate eyes, so wear eye protection. Hydrogen is flammable, so exclude ignition sources.
Quick check
What is wrong with “change the acid and see what happens”?
Check after attempting
It lacks a defined variable, measurements, controlled quantities and a reproducible method.
Burette reading practice
Read the bottom of each meniscus. Each small division is 0.1 cm³. Estimate to the nearest half division and calculate final minus initial.
Scale-reading model only. Practise filling, rinsing, clamping and recognising endpoints with your teacher’s approved apparatus procedure.
Explore a model, then investigate先探索模型，再设计实验
Predict what a variable will change, test it in a simulation, then explain what the model shows and what it leaves out.预测变量的影响，在模拟中检验，再解释模型展示了什么、有哪些局限。