This module covers the fourth part of the CSCA Chemistry syllabus, Chemical Experiments and Applications: laboratory safety and the use of apparatus, the preparation and identification of common gases, the separation and purification of substances, and the chemistry of industrial processes such as ammonia synthesis.
Experiment questions reward one habit: for every operation, ask what would go wrong if it were done differently. Why is acid added to water and not the reverse? Why does the gas enter through the long tube? Why is Na₂CO₃ added after BaCl₂? Once you know the reason behind a rule, you no longer have to memorise the rule, and you can handle set-ups you have never seen.
There are four lessons: Lab Safety & Apparatus, Preparing & Collecting Gases, Separation, Purification & Ion Tests and Industrial Chemistry. Chinese terms are given in brackets for students who sit the paper in Chinese, for example 定容 (making up to the mark) and 向上排空气法 (upward displacement of air).
The syllabus lists four topics under Chemical Experiments and Applications: laboratory safety and the use of apparatus, the preparation and identification of common gases, the separation and purification of substances, and the analysis of industrial chemical processes such as ammonia synthesis. In single-answer multiple-choice form, questions on these topics can ask you to judge whether an operation is correct, choose apparatus or reagents for a task, decide whether an error makes a result too high or too low, identify a substance from test results, read an apparatus diagram or a data graph, or explain the choice of industrial conditions.
Most of these questions reward reasoning more than recall: if you know why each rule exists (what would explode, crack, dissolve, react or be lost), you can work out an unfamiliar case. The calculations are short: solution concentrations, masses from an equation, percentage yield and atom economy.
Many experiment questions are really questions about apparatus: which vessel can be heated, which instrument is precise enough, which must be checked for leaks, which must be rinsed with its own solution. Learn each piece by its job and by its rules.
| Heated directly | Heated on a gauze | Never heated |
|---|---|---|
| test tube, evaporating dish, crucible, combustion spoon | beaker, flask, conical flask | measuring cylinder, volumetric flask, burette, reagent bottle |
Check for leaks before use (检漏): the volumetric flask, the separating funnel and the burette, that is, everything with a stopper or tap that must hold liquid.
Rinse with the solution it will hold (润洗): the burette and the pipette only. The conical flask is NOT rinsed with the sample and the volumetric flask is NOT rinsed with the solution, because the extra solute left on the walls would cause an error. A conical flask or volumetric flask that is wet with distilled water causes no error.
💡Know each piece by its job and its rules: test tubes, evaporating dishes and crucibles are heated directly, beakers and flasks on a gauze, measuring glassware never. Precision is 0.1 g (pan balance), 0.1 mL (measuring cylinder) and 0.01 mL (burette, pipette). Leak-test anything with a stopper or tap, and rinse only the burette and pipette with their own solution.
📋 Key Formulas
Precision: pan balance 0.1 g | measuring cylinder 0.1 mL | burette, pipette 0.01 mL | Leak-test: volumetric flask, separating funnel, burette | Rinse with own solution: burette, pipette
📝 Worked Example 1
Example 1: A student records the volume of NaOH used in a titration as 22.6 mL. What is wrong?
Step 1: A burette is read to 0.01 mL, so the record must have two decimal places.
Step 2: It should be written 22.60 mL. A value with one decimal place, such as 22.6 mL, is the precision of a measuring cylinder.
📝 Worked Example 2
Example 2: Which burette should hold acidified KMnO₄ solution, and which should hold NaOH solution?
Step 1: KMnO₄ is a strong oxidising agent and attacks the rubber tube of a base burette, so it goes in the acid burette (glass stopcock).
Step 2: NaOH attacks glass and makes a ground-glass stopcock stick, so it goes in the base burette.
📝 Worked Example 3
Example 3: Choose the apparatus to heat 2 g of CuSO₄·5H₂O strongly until all its water is driven off, and to weigh the residue accurately.
Step 1: Strong heating of a solid needs a crucible on a pipe-clay triangle on a tripod, heated directly.
Step 2: Move the hot crucible with crucible tongs and let it cool in a desiccator, so that the anhydrous CuSO₄ cannot take up water from the air.
Step 3: Weigh, heat again, cool and weigh again until two masses agree (heating to constant mass).
🧠When an option says a piece of glassware is used to dissolve, dilute, react or heat something, check that it is not a measuring cylinder or a volumetric flask: those two only measure.
🧠Read the decimal places in the question: 25.00 mL points to a burette or pipette, 25.0 mL to a measuring cylinder, 2.0 g to a pan balance.
⚠️Rinsing the conical flask with the sample. Only the burette and pipette are rinsed with their own solution; a rinsed conical flask holds extra sample and gives a high result.
⚠️Putting NaOH in an acid burette, or KMnO₄ in a base burette. Alkali makes a glass stopcock stick; an oxidant attacks rubber.
⚠️Heating a beaker directly in the flame. Beakers and flasks need a gauze to spread the heat.
🎯 Try This Yourself
Which of these can be heated directly in a flame: beaker, crucible, volumetric flask, test tube, conical flask?
Open and read all sections to complete this module