📚 Cambridge Lower Secondary Complete Chemistry Practical Operations | 剑桥初中化学实验操作指南
Practical work is at the heart of the Cambridge Lower Secondary Complete Chemistry course. Through hands‑on experiments you learn how to observe, measure, separate substances, identify gases and record data safely. This article summarises the key practical operations and techniques covered in the Student Book (2nd edition) to help you build confidence in the laboratory.
实验操作是剑桥初中化学课程的核心。通过动手实验，你将学会如何安全地进行观察、测量、分离物质、鉴定气体和记录数据。本文总结了学生用书（第二版）中的主要实验操作与技术，助你在实验室中建立信心。
1. Laboratory Safety and Equipment | 实验室安全与设备
Before any experiment, make sure you wear safety goggles and a lab coat. Tie back long hair, tuck in loose clothing and never eat or drink in the lab. Always read the risk assessment and follow your teacher’s instructions.
进行任何实验前，务必戴好护目镜和实验服。长发应束起，宽松衣物要整理好，实验室内绝对禁止饮食。务必阅读风险评估并遵从教师指导。
Common apparatus includes beakers, test tubes, conical flasks, Bunsen burners, tripods, wire gauze, measuring cylinders, evaporating dishes, filter funnels and thermometers. Handle glassware carefully and report any breakages immediately.
常用仪器包括烧杯、试管、锥形瓶、本生灯、三脚架、石棉网、量筒、蒸发皿、漏斗和温度计。使用玻璃仪器时要小心，如有破损立即报告。
Know the location of safety equipment: fire extinguisher, fire blanket, eye‑wash station and first‑aid kit. If a chemical splashes on your skin, rinse with plenty of water.
了解安全设备的位置：灭火器、灭火毯、洗眼器和急救箱。如果化学品溅到皮肤上，立即用大量清水冲洗。
2. Heating Techniques: Using a Bunsen Burner | 加热技术：本生灯的使用
Light the Bunsen burner with the air hole closed to obtain a yellow, luminous flame. This safety flame is highly visible but not very hot. Open the air hole to get a roaring blue flame for strong heating; the hottest part is just above the inner blue cone.
点燃本生灯时，应先关闭气孔，得到黄色的安全焰。这种火焰醒目但温度不高。打开气孔可获得强力的蓝色火焰，温度最高处位于内层蓝色锥形焰的顶端。
When heating a liquid in a test tube, hold it with a test‑tube holder and point the mouth away from yourself and others. Move the tube gently in and out of the flame to avoid bumping. Never look down the tube.
加热试管中的液体时，用试管夹夹持，管口不要对着自己或他人。轻轻将试管从火焰中移进移出，防止暴沸。切勿俯视管口。
For heating solids or larger volumes, place the container on a tripod and gauze. Stir the liquid steadily with a glass rod to distribute heat evenly.
加热固体或较大体积液体时，将容器放在三脚架和石棉网上。用玻璃棒均匀搅拌，使热量分布均匀。
3. Measuring Temperature and Using Thermometers | 测量温度与温度计的使用
A laboratory thermometer (usually –10 °C to 110 °C) must be placed in the substance you are measuring. The bulb should be fully immersed but not touching the container walls. Wait until the reading is steady before recording.
实验室温度计（通常量程为 –10 °C 至 110 °C）应浸入待测物质中。感温泡要完全浸没，但不要接触容器壁。待读数稳定后再记录。
Read the scale at eye level, perpendicular to the thermometer. Record the temperature with the unit °C and note your readings in a neat table. Avoid handling the bulb with warm fingers before measurement.
读数时视线应与刻度垂直，保持水平。记录温度时注明单位 °C，并将数据整齐填入表格。测量前避免用温暖的手指触碰感温泡。
- Typical experiments: measuring the temperature change when a salt dissolves or when a reaction occurs. Always repeat and take an average.
- 典型实验：测定盐类溶解或发生反应时的温度变化。务必重复实验并取平均值。
4. Dissolving and Stirring | 溶解与搅拌
When dissolving a solid in a liquid, add the solid in small portions while stirring continuously with a glass rod. Crush large crystals first to increase the surface area and speed up dissolving.
将固体溶于液体时，应分批少量加入，并用玻璃棒不断搅拌。大颗粒晶体可先研细，以增大表面积、加快溶解速度。
For most salts, heating the solvent gently can increase the solubility. Use a water bath if flammable solvents are involved. Once dissolution is complete, you may filter or evaporate the solution as required.
对大多数盐类，微微加热溶剂可提高溶解度。若使用易燃溶剂，应使用水浴加热。溶解完全后，可按需要过滤或蒸发溶液。
Record the maximum mass of solid that dissolves in a fixed volume of water at a given temperature. This data helps you plot solubility curves later.
记录给定温度下一定体积水最多可溶解的固体质量，这些数据可用来绘制溶解度曲线。
5. Filtration: Separating an Insoluble Solid from a Liquid | 过滤：分离不溶性固体与液体
Fold a filter paper into a cone, place it in a filter funnel and moisten it with a little solvent. Position the funnel over a clean beaker. Pour the mixture slowly down a glass rod into the funnel to prevent splashing.
将滤纸折成圆锥形，放入漏斗中，用少量溶剂润湿。漏斗下方放置洁净的烧杯。用玻璃棒引流，将混合物缓慢倒入漏斗，以防飞溅。
The residue (insoluble solid) stays on the filter paper while the filtrate (clear liquid) passes through. Wash the residue with a small amount of distilled water to remove any remaining soluble impurities.
不溶性固体（滤渣）留在滤纸上，澄清的滤液则通过滤纸。用少量蒸馏水洗涤滤渣，以除去残留的可溶性杂质。
Filtration is used to purify sandy salt water, to collect a precipitate, or to separate chalk from water. The filter paper’s pores must be finer than the solid particles.
过滤用于提纯含泥沙的盐水、收集沉淀或从水中分离粉笔末。滤纸的孔径必须小于固体颗粒。
6. Evaporation and Crystallisation | 蒸发与结晶
To obtain a soluble salt from its solution, pour the filtrate into an evaporating dish and heat gently on a water bath. When a thin crust of crystals appears at the edge, stop heating and let the rest of the solvent evaporate slowly.
从溶液中得到可溶性盐时，将滤液倒入蒸发皿，在水浴上温和加热。当皿边出现一层薄晶膜时，停止加热，让剩余溶剂慢慢自然蒸发。
Large, well‑formed crystals are produced by slow cooling of a hot, saturated solution. Leave the solution undisturbed and allow it to cool to room temperature. Filter the crystals and dry them between sheets of filter paper.
缓慢冷却热的饱和溶液可生成大而规整的晶体。将溶液静置，自然冷却至室温。过滤出晶体，夹在两片滤纸间吸干。
If the salt decomposes on strong heating, always use a water bath or an electric heater set to a low temperature. Never evaporate to complete dryness when making crystals.
如果盐在强热下会分解，务必使用水浴或低温电热板。制备晶体时切勿蒸干至完全干燥。
7. Chromatography: Separating Coloured Mixtures | 色谱法：分离有色混合物
Draw a pencil baseline near the bottom of a strip of chromatography paper. Pencil is insoluble and will not run. Place a small spot of the mixture and spots of reference dyes on the line. Dip the paper in a suitable solvent, keeping the baseline above the solvent surface.
在色谱纸条靠近底端处用铅笔画一条基线（铅笔不溶于水，不会扩散）。在基线上点上混合物和参比染料的微小斑点。将纸条垂直插入合适的溶剂中，确保基线在液面之上。
The solvent rises by capillary action, carrying the dyes at different speeds. When the solvent front has nearly reached the top, remove the paper and mark the solvent front in pencil. Hang the strip to dry.
溶剂因毛细作用上升，各染料随之上移的速度不同。当溶剂前沿接近顶端时，取出纸条，用铅笔标记溶剂前沿位置，悬挂晾干。
Calculate the Rf value for each spot: Rf = distance moved by the spot ÷ distance moved by the solvent front. Compare Rf values to identify unknown components.
计算每个斑点的比移值：Rf = 斑点移动距离 ÷ 溶剂前沿移动距离。对比Rf值可鉴定未知组分。
8. Preparation and Collection of Gases | 气体的制备与收集
Common gases prepared in the lab include oxygen (from hydrogen peroxide and manganese dioxide catalyst), carbon dioxide (from calcium carbonate and dilute hydrochloric acid) and hydrogen (from zinc and dilute sulfuric acid). Fit a delivery tube to the reaction flask.
实验室常制备的气体有氧气（过氧化氢加二氧化锰催化）、二氧化碳（碳酸钙与稀盐酸）和氢气（锌与稀硫酸）。将导管连接到反应瓶上。
| Gas | Collection method | Why |
|---|---|---|
| Oxygen (O₂) | Over water (downward displacement of water) | Slightly soluble in water |
| Carbon dioxide (CO₂) | Upward delivery (downward displacement of air) | Denser than air, slightly soluble |
| Hydrogen (H₂) | Downward delivery (upward displacement of air) | Less dense than air |
Always check that the apparatus is air‑tight before starting. Collect a test tube full of the gas and keep it upside down or upright as needed. Label all collection tubes.
实验前务必检查装置气密性。收集一试管气体，根据气体密度决定正立或倒放。所有收集管都应贴上标签。
9. Testing for Common Gases | 常见气体的检验
Insert a glowing splint into a sample of gas: if the splint relights, the gas is oxygen. A burning splint held at the mouth of a test tube that burns with a squeaky pop indicates hydrogen.
将带火星的木条伸入气体中，木条复燃则说明是氧气。点燃的木条放在试管口，若听到轻微爆鸣声，则气体是氢气。
Bubble the gas through limewater (calcium hydroxide solution). A white precipitate turns the limewater cloudy or milky, confirming carbon dioxide. Do not confuse this with other precipitates.
将气体通入石灰水（氢氧化钙溶液），若出现白色沉淀使石灰水变浑浊，则证明有二氧化碳。注意不要与其他沉淀混淆。
For chlorine, place a piece of damp blue litmus paper in the gas; it first turns red then bleaches white. Ammonia turns damp red litmus paper blue and has a pungent odour.
检验氯气时，将湿润的蓝色石蕊试纸放入气体中，试纸先变红后褪色漂白。氨气使湿润的红色石蕊试纸变蓝且有刺激性气味。
Always use only a small amount of gas for these tests. Wear safety goggles because some gases, like chlorine and nitrogen dioxide, are toxic.
这些检验只用少量气体。务必佩戴护目镜，因为氯气、二氧化氮等气体有毒。
10. Using Acid–Base Indicators and pH Testing | 酸碱指示剂与pH值测定
Indicators such as litmus, phenolphthalein and methyl orange change colour in acidic or alkaline solutions. Blue litmus turns red in acid; red litmus turns blue in alkali. Phenolphthalein gives a pink colour in alkali but remains colourless in acid.
石蕊、酚酞和甲基橙等指示剂在酸性或碱性溶液中会发生颜色变化。蓝色石蕊在酸中变红，红色石蕊在碱中变蓝。酚酞在碱性溶液中呈粉红色，在酸中无色。
Universal indicator is a mixture of indicators that gives a wide range of colours corresponding to pH values from 0 (strong acid) to 14 (strong alkali). Match the colour to a pH colour chart.
通用指示剂是混合指示剂，根据pH值从0（强酸）到14（强碱）显示丰富颜色。将颜色与标准色卡比对即可读出pH。
To measure pH more precisely, use a pH meter calibrated with buffer solutions. Rinse the probe with distilled water before and after each measurement and store it properly.
要更精确测定pH，可使用经缓冲溶液校准的pH计。每次测量前后用蒸馏水冲洗探头并妥善保存。
11. Making Solutions and Dilutions | 配制和稀释溶液
To prepare a salt solution of a known concentration, weigh the required mass of solid on a balance. Tip it into a beaker, add a little distilled water and stir to dissolve. Transfer the solution to a volumetric flask and fill to the mark with distilled water.
配制已知浓度的盐溶液时，用天平称取所需质量的固体。倒入烧杯，加少量蒸馏水搅拌溶解。将溶液转移至容量瓶中，加蒸馏水定容至刻度线。
When diluting a solution, always add concentrated acid to water slowly while stirring, never the reverse, because the reaction is highly exothermic. Rinse the graduated pipette with the solution before measuring.
稀释溶液时，必须将浓酸缓慢加入水中并搅拌，绝不能将水倒入浓酸，因为该过程大量放热。测量前用待取液润洗刻度吸管。
Label the bottle with the name of the solute, concentration and date. Keep it stoppered and store according to the safety data sheet.
在瓶身标签上注明溶质名称、浓度和日期。盖紧瓶塞，根据安全数据表要求储存。
12. Recording Data and Drawing Conclusions | 记录数据与得出结论
Draw a clear results table with headings and units before you start the experiment. Record all measurements promptly and honestly. Use a ruler when drawing tables and graphs. Keep a well‑organised lab notebook.
实验开始前，先绘制带有表头和单位的清晰结果表格。及时、诚实地记录所有测量数据。画表格和图表时使用直尺。保持实验记录本井井有条。
Identify any anomalous results and, if time allows, repeat the measurement. Calculate the mean of the results, excluding outliers, and express it to an appropriate number of significant figures.
找出异常数据，如时间允许应重新测量。计算剔除异常值后的平均值，并以适当的有效数字位数表示。
State a conclusion that refers directly to the aim and data. Evaluate the reliability of the method, suggest possible sources of error and propose improvements for future work.
得出结论时，要直接联系实验目的和数据。评估方法的可靠性，指出可能的误差来源，并对后续实验提出改进建议。
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