📚 Doing an Investigation in Chemistry | 化学实验探究方法
A chemistry investigation is a step-by-step way of answering a scientific question. You change one variable, measure another, and keep everything else the same, so that any change you see can be blamed on the one factor you chose. This article explains how to plan, carry out, record and evaluate an investigation, using KS3 chemistry examples such as dissolving sugar, reacting marble with acid and burning fuels.
化学探究是回答科学问题的一种循序渐进的科学方法。你改变一个变量，测量另一个变量，并保持其他条件不变，这样观察到的任何变化都能归因于你所选的那一个因素。本文用 KS3 化学中的实例，例如方糖溶解、大理石与酸反应、燃料燃烧，解释如何计划、实施、记录和评估一个探究。
The skills below are the same ones examined in practical questions, required practicals and later GCSE work. Learn the vocabulary carefully, because marks are often given for naming variables and units correctly rather than for the final number.
下面这些技能与实验题、必做实验以及之后的 GCSE 学习中考查的技能完全一致。请认真掌握术语，因为得分点常常在于正确命名变量和单位，而不在于最后那个数字。
1. Asking a Scientific Question | 提出科学问题
The investigation begins with a testable question. It must include the thing you will change and the thing you will measure. For example, 'How does the temperature of water affect the time taken for a sugar cube to dissolve?' is clear and testable because both parts can be measured with apparatus.
探究开始于一个可检验的问题。问题中必须包含你将要改变的因素和你将要测量的因素。例如，'水的温度如何影响方糖溶解所需的时间？' 这个问题清晰且可检验，因为两个部分都能用仪器测量。
Avoid questions that are too broad or based on opinion, such as 'Which liquid is best?' or 'Is dissolving fun?'. These have no single measurable answer, so no amount of careful work can settle them. Instead, ask questions that can be answered with measurements and repeated trials.
避免过于宽泛或基于观点的问题，例如 '哪种液体最好？' 或 '溶解有趣吗？'。这类问题没有唯一可测量的答案，再细致的操作也无法解决。相反，要提出可以用测量和重复实验来回答的问题。
If your topic is too wide, narrow it down to one independent variable. For example, instead of asking about dissolving in general, focus on how temperature affects the dissolving time of a fixed mass of sugar in a fixed volume of water.
如果主题太宽泛，就把它缩小到一个自变量。例如，与其笼统地研究溶解，不如专注于温度如何影响固定质量糖在固定体积水中的溶解时间。
2. Variables: Independent, Dependent and Control | 变量：自变量、因变量和控制变量
In a fair experiment you must identify three types of variable. The independent variable is the one you change on purpose. The dependent variable is the one you measure or observe. Control variables are all the other factors that must be kept the same so that the test is fair.
在公平实验中，你必须识别三种变量。自变量是你有意改变的那个因素；因变量是你测量或观察的那个因素；控制变量是所有必须保持不变的其他因素，以保证实验公平。
| Variable type | 变量类型 | Meaning | 含义 | Sugar example | 方糖实例 |
|---|---|---|
| Independent 自变量 | The factor you change | 你主动改变的因素 | Water temperature | 水的温度 |
| Dependent 因变量 | The factor you measure | 你测量的因素 | Time to dissolve | 溶解所需时间 |
| Control 控制变量 | Factors kept constant | 保持不变的因素 | Mass of sugar, volume of water, stirring | 糖的质量、水的体积、搅拌方式 |
If a control variable is not held constant, the experiment is not a fair test and the conclusion becomes unreliable. For example, if you stir one beaker but not the other, you cannot tell whether temperature or stirring caused the change in dissolving time.
如果某个控制变量没有保持不变，实验就不是公平检验，结论也就不可靠。例如，如果你搅拌其中一只烧杯却不搅拌另一只，你就无法判断溶解时间的变化是由温度还是由搅拌造成的。
3. Hypothesis and Prediction | 假设与预测
A hypothesis is a scientific prediction with a reason, written before any data are collected. It should link your existing chemistry knowledge to the variables in the investigation, and it should be possible to prove it wrong with evidence.
假设是带有理由的科学预测，必须在收集数据之前写出。它应把已有的化学知识与探究中的变量联系起来，并且必须有可能用证据证明它是错的。
A good hypothesis uses an 'if ... then ... because ...' structure. For dissolving sugar: 'If the water temperature is higher, then the sugar will dissolve faster, because the water particles have more kinetic energy and collide with the sugar surface more often.'
好的假设使用 '如果……那么……因为……' 的结构。以方糖溶解为例：'如果水的温度更高，那么糖会溶解得更快，因为水分子具有更多动能，更频繁地撞击糖的表面。'
A prediction goes one step further and states the expected result, such as 'sugar in 60 °C water will dissolve in about half the time it takes in 20 °C water'. A prediction can be checked directly against the data you collect.
预测则更进一步，给出预期的结果，例如 '60 °C 水中的糖溶解时间约为 20 °C 水中所需时间的一半'。预测可以直接与你收集的数据进行对照。
4. Planning a Fair Test and Risk Assessment | 设计公平实验与风险评估
A plan is a numbered list of steps that another student could follow exactly. Each step should say what apparatus is used, what quantity is measured, and how the control variables are kept the same. A clear plan produces reliable data; a vague plan produces results that cannot be trusted.
实验计划是一份编号步骤清单，另一位同学照着做能得到同样的结果。每一步都应说明使用什么仪器、测量什么量、以及如何保持控制变量不变。清晰的计划产生可靠数据，含糊的计划产生不可信的结果。
Before starting, carry out a risk assessment. Hot water can scald, glassware can break, and acids can irritate skin. Typical safety actions are wearing goggles, using a heatproof mat, handling hot beakers with tongs, tying back long hair and reporting spills to the teacher at once.
开始之前要进行风险评估。热水会烫伤，玻璃器皿会破碎，酸会刺激皮肤。常见的安全措施包括佩戴护目镜、使用隔热垫、用坩埚钳夹取热烧杯、束起长发，以及一旦洒出立即报告老师。
Also decide the range and interval of your independent variable before you begin. Testing every 10 °C from 20 °C to 60 °C gives five data points, which is enough to see a pattern. Testing only 20 °C and 21 °C would tell you almost nothing.
还要在开始前确定自变量的范围和间隔。从 20 °C 到 60 °C 每隔 10 °C 测一次，可得到五个数据点，足以看出规律。只测 20 °C 和 21 °C 几乎得不出任何结论。
5. Apparatus and Measurement Techniques | 仪器与测量技术
Choose apparatus that matches the size of the quantity you are measuring. A 250 cm³ beaker is poor for measuring 20 cm³ of water, while a 25 cm³ measuring cylinder reads it much more precisely. Digital balances reading to 0.01 g are used for small masses.
选择与所测数量大小相匹配的仪器。用 250 cm³ 烧杯量取 20 cm³ 水很不精确，而 25 cm³ 量筒则精确得多。测量小质量应使用读数到 0.01 g 的电子天平。
Read scales correctly: view a measuring cylinder at eye level and read the bottom of the meniscus, read a thermometer after the liquid has stopped changing, and start a stopwatch at the moment the sugar is added. Reaction time adds a small random error of about 0.2 s to each timing.
正确读取刻度：读数时视线与量筒内凹液面最低处齐平，待液体温度稳定后再读温度计，并在加入方糖的瞬间开始计时。人的反应时间会给每次计时带来约 0.2 s 的随机误差。
Precision and accuracy are not the same thing. Precision is how small the scale divisions are; accuracy is how close a reading is to the true value. A balance with 0.01 g divisions is precise, but if it has not been zeroed it will still be inaccurate.
精密度和准确度不是一回事。精密度指刻度分度有多小；准确度指读数与真值的接近程度。分度为 0.01 g 的天平很精密，但如果没有归零，读数仍不准确。
6. Carrying Out the Method | 实施实验方法
During the practical, keep every condition identical except the independent variable. Use the same mass of sugar, the same volume of water, the same type of beaker and the same stirring method for every trial. Change only the temperature.
实验过程中，除自变量以外的一切条件都必须完全一致。每次实验使用相同质量的糖、相同体积的水、相同类型的烧杯和相同的搅拌方式，只改变温度。
Repeat each temperature at least three times and calculate a mean. Repeats reduce the effect of random errors such as slightly different starting times or small variations in room temperature, and they allow an anomalous result to be spotted.
每个温度至少重复三次并计算平均值。重复实验可以减小随机误差的影响，例如起始时刻略有差异或室温的小波动，同时也能发现异常值。
Record the data immediately, in pencil, in the table you prepared in advance. Never rely on memory, and never change a reading to make the pattern look neater. If a result is clearly anomalous, repeat that one measurement rather than deleting it silently.
数据要立即用铅笔记录在事先准备好的表格中。绝不要凭记忆，也绝不要为了让规律看起来更整齐而修改读数。如果某个结果明显异常，应重做那一次测量，而不是悄悄删掉它。
7. Recording Data in Tables | 用表格记录数据
A results table has the independent variable in the first column and the dependent variable in the next column, with the mean in a final column. Units belong in the column heading, not next to every number, and the number of decimal places should be consistent.
数据表第一列放自变量，下一列放因变量，最后一列放平均值。单位写在列标题中，而不是写在每个数字旁边，小数位数应保持一致。
Record both quantitative and qualitative observations. Quantitative data are numbers, such as 42.3 s or 1.25 g. Qualitative observations are descriptions, such as 'the solution turned colourless' or 'bubbles were given off steadily'. Both types of evidence can support a conclusion.
既要记录定量数据，也要记录定性观察。定量数据是数字，例如 42.3 s 或 1.25 g；定性观察是描述，例如 '溶液变为无色' 或 '持续均匀地放出气泡'。两类证据都能支持结论。
If you calculate a rate, show the equation you used so the marker can see your reasoning. For dissolving, the average rate of mass loss can be written as:
如果你要计算速率，请写出所用公式，让阅卷人看到你的思路。以溶解为例，平均质量损失速率可写为：
average rate = Δmass ÷ Δtime
State the unit of a rate clearly, for example g s⁻¹ or g min⁻¹. A rate is always a change in one quantity divided by the time taken for that change.
速率的单位要写清楚，例如 g s⁻¹ 或 g min⁻¹。速率总是一个量的变化量除以该变化所用的时间。
8. Drawing Graphs and Spotting Patterns | 绘图与发现规律
Graphs make patterns visible. Put the independent variable on the x-axis and the dependent variable on the y-axis, label both axes with the quantity and its unit, and choose a scale that fills most of the grid. Plot points with a small cross or a clear dot.
图像让规律一目了然。自变量放在 x 轴，因变量放在 y 轴，两个轴都要标注物理量及其单位，并选择能占满大部分坐标纸的刻度。数据点用小叉或清晰的圆点标出。
Draw a line of best fit through the points rather than joining dot to dot. Use a straight line when the trend looks linear and a smooth curve when it bends. Ignore an obvious anomalous point when drawing the line, but keep the point on the graph and mention it in your evaluation.
应通过数据点画一条最佳拟合线，而不是把点逐个连成折线。趋势呈线性时画直线，曲线弯曲时画平滑曲线。绘图时忽略明显异常的点，但要在图上保留该点，并在评估中加以说明。
Then describe the trend in words. For dissolving sugar, the graph usually shows that as temperature rises, dissolving time falls quickly at first and then levels off. This shape suggests the effect is greatest at low temperatures and that another factor, such as stirring, limits the rate at high temperatures.
然后用文字描述趋势。对于方糖溶解，图像通常显示：温度升高时，溶解时间起初迅速下降，随后趋于平缓。这种形状说明低温段温度的影响最大，而高温段的速率还受到其他因素（如搅拌）的限制。
9. Writing a Conclusion | 得出结论
A conclusion answers the original question using the data you collected. It should quote at least one pair of numbers as evidence, describe the relationship between the variables, and state whether the hypothesis was supported.
结论要用你收集的数据回答最初的问题。它应至少引用一对数字作为证据，描述变量之间的关系，并说明假设是否得到支持。
For example: 'As the water temperature increased from 20 °C to 60 °C, the mean dissolving time decreased from 68.4 s to 24.1 s. This supports the hypothesis that higher temperatures increase the rate of dissolving.' Notice that the numbers carry the argument.
例如：'当水温从 20 °C 升高到 60 °C 时，平均溶解时间从 68.4 s 下降到 24.1 s。这支持了温度升高加快溶解速率的假设。' 注意，是数字在支撑整个论证。
Add a scientific explanation. In this case, higher temperature gives water particles more kinetic energy, so they move faster and collide with the sugar surface more frequently, so the sugar breaks up and spreads through the water more quickly.
还要加入科学解释。在此例中，温度升高使水分子获得更多动能，运动更快，更频繁地撞击糖的表面，因此糖更快地碎裂并扩散到水中。
10. Evaluating the Investigation | 评估探究过程
An evaluation judges how trustworthy the results are and suggests specific improvements. Identify sources of error, say whether each one is random or systematic, and explain how it affected the data.
评估要判断结果的可信程度并提出具体改进建议。要指出误差来源，说明每个误差是随机误差还是系统误差，并解释它如何影响数据。
Random errors, such as reaction time when starting the stopwatch or small variations in room temperature, scatter results above and below the true value. Repeating measurements and taking a mean reduces their effect.
随机误差，例如按下秒表时的反应时间或室温的微小波动，会使结果在真值上下分散。重复测量并取平均值可以减小其影响。
Systematic errors push every result in the same direction. A thermometer that reads 2 °C too low, or a balance that was not zeroed, makes every measurement wrong in the same way. Repeating cannot fix a systematic error; the instrument must be calibrated or the method changed.
系统误差使所有结果朝同一方向偏移。温度计读数偏低 2 °C，或天平未归零，会让每次测量以相同方式出错。重复实验无法修正系统误差，必须校准仪器或改变方法。
Finally, state the limits of your conclusion. If you only tested 20 °C to 60 °C in water, you cannot claim that the same pattern holds for oil at 150 °C, or that dissolving time would fall to zero at 100 °C. Suggest a further experiment, such as testing a wider temperature range or using a water bath to control temperature more precisely.
最后要说明结论的适用范围。如果你只在水中测试了 20 °C 到 60 °C，就不能声称同样的规律适用于 150 °C 的油，也不能说 100 °C 时溶解时间会降为零。可提出进一步实验，例如扩大温度范围，或用恒温水浴更精确地控制温度。
11. Common KS3 Investigations and Exam Skills | 常见 KS3 探究与考试技巧
ric acid affects the rate of reaction with marble chips, CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂; how surface area affects reaction rate; how the mass of fuel affects the temperature rise of water; and how chromatography separates the dyes in an ink.
KS3 课程在许多主题中反复使用同一套探究结构：温度如何影响溶解时间；盐酸浓度如何影响它与大理石碎块（CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂）的反应速率；表面积如何影响反应速率；燃料质量如何影响水温升高；以及色谱法如何分离墨水中的色素。
Exam command words matter. 'Describe' means say what happens; 'explain' means give a scientific reason; 'compare' means give similarities and differences; 'evaluate' means judge reliability and suggest improvements. Answer the command word that is actually printed.
考试中的指令词很重要。'描述' 指说明发生了什么；'解释' 指给出科学理由；'比较' 指说出相同点和不同点；'评估' 指判断可靠性并提出改进建议。要针对题目中实际出现的指令词作答。
- Always name the independent and dependent variables before describing the method. | 描述方法之前，先写出自变量和因变量。
- Give units for every measurement, using cm³, g, s, °C or g s⁻¹. | 每个测量值都要带单位，如 cm³、g、s、°C 或 g s⁻¹。
- Use data from the table or graph in your conclusion, never vague words such as 'it got faster'. | 结论中要引用表格或图像中的数据，绝不用 '变快了' 这类含糊说法。
- Suggest one realistic improvement linked to a named error, not a general comment such as 'be more careful'. | 提出一条与具体误差相关的可行改进，而不是 '更小心一点' 这类泛泛之谈。
Keep a checklist in your notebook: question, hypothesis, variables, risk assessment, method, results table, graph, conclusion, evaluation. If you can produce all nine parts confidently, you can handle any practical question on a KS3 or GCSE chemistry paper.
在笔记本里保留一份清单：问题、假设、变量、风险评估、方法、数据表、图像、结论、评估。如果你能自信地完成这九个部分，任何 KS3 或 GCSE 化学试卷上的实验题你都能应对。
Published by TutorHao | KS3 Chemistry Revision Series | aleveler.com
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