WJEC Year 12 Science: Key Points for Practical Assessment | WJEC 12年级科学：实验考核要点

📚 WJEC Year 12 Science: Key Points for Practical Assessment | WJEC 12年级科学：实验考核要点

In Year 12 WJEC Science, practical assessments test your ability to work safely, collect data, and think like a scientist. This guide covers the essential skills you must demonstrate, from planning an investigation to evaluating results, ensuring you can approach your practical tasks with confidence.

在 WJEC 12 年级科学中，实验考核测试你安全操作、收集数据以及像科学家一样思考的能力。本指南涵盖你必须展示的关键技能，从规划探究到评估结果，确保你能自信地应对实验任务。

1. Planning a Valid Investigation | 规划有效的探究

Every investigation begins with a clear aim and a testable hypothesis. Write your hypothesis as a prediction, for example ‘If the concentration of the reactant is doubled, the initial rate of reaction will also double.’

每次探究都始于明确的目的和可验证的假设。将你的假设写成一个预测，例如“如果反应物的浓度加倍，则初始反应速率也将加倍”。

Identify the independent variable you will change, the dependent variable you will measure, and list at least three control variables that must be kept constant to ensure a fair test.

确定你将改变的自变量、将要测量的因变量，并列出至少三个必须保持恒定的控制变量，以确保公平测试。

Select the most appropriate apparatus for the measurements required, justifying your choices with reference to precision. For instance, a 50 cm³ burette reads to 0.05 cm³, while a 25 cm³ measuring cylinder only reads to ±1 cm³.

选择最适合所需测量的仪器，并以精密度为依据证明你的选择。例如，50 cm³ 滴定管的读数精度为 0.05 cm³，而 25 cm³ 量筒的读数精度仅为 ±1 cm³。

Always include a step-by-step method that another student could follow. Use numbered steps, and mention any preliminary runs needed to determine a suitable range of the independent variable.

始终包含一个其他同学能遵循的、分步详细的方法。使用编号步骤，并提及任何用来确定自变量合适范围的预备实验。

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2. Variables and Controls | 变量与控制

Control variables are just as important as the independent variable. In an enzyme experiment, controlling pH, temperature, and substrate concentration prevents unwanted variables from influencing your results.

控制变量与自变量同样重要。在酶促实验中，控制 pH、温度和底物浓度可防止无关变量影响你的结果。

Use the correct terminology: a control experiment is one where the independent variable is set to zero or a standard condition, used to verify that the effect you observe is real.

使用正确术语：对照实验是将自变量设为零或标准条件的实验，用于验证你所观察到的效应是真实存在的。

When designing a table for results, label each column with the physical quantity and its unit, and ensure you have space for repeated readings of the dependent variable.

设计结果表格时，用物理量和单位标注每一列，并确保有为因变量的重复读数预留空间。

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3. Risk Assessment and Safe Practice | 风险评估与安全操作

Before any practical, you must complete a risk assessment. Identify each hazard, the associated risk, and the control measure you will take to minimise that risk.

在任何实验之前，你必须完成风险评估。识别每个危险源、相关风险以及你将采取的用以尽可能降低风险的控制措施。

Hazards can include hot surfaces, corrosive chemicals such as 2 mol dm⁻³ HCl, sharp objects like scalpels, or heavy masses. Always wear eye protection and tie back long hair.

危险源可能包括热表面、腐蚀性化学品（如 2 mol dm⁻³ HCl）、锋利的物体（如解剖刀）或重物。务必始终佩戴护目镜并束好长发。

Know the safety symbols used on chemical bottles, such as the flame symbol for flammable substances and the exclamation mark for irritants. Mention them in your plan.

了解化学试剂瓶上使用的安全标志，例如易燃物质的火焰标志和刺激性物质的感叹号标志。在你的计划中提及这些。

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4. Making Accurate Measurements | 进行精确测量

Accuracy of measurement depends on choosing the right instrument. For length, use a metre rule for distances over 20 cm, but use digital callipers or a micrometer for smaller lengths, noting the resolution of each instrument.

测量精度取决于选择合适的仪器。测量长度时，超过 20 cm 的用米尺，但较小的长度应使用电子游标卡尺或千分尺，并记录每种仪器的分辨率。

When recording a volume from a burette or measuring cylinder, always read the bottom of the meniscus at eye level. For a colourimeter, always zero the instrument with a blank before taking readings.

读取滴定管或量筒的体积时，始终在视线高度处读出弯月面的底部。使用比色计时，务必在读数前用空白样品将仪器调零。

Take repeat readings and calculate a mean. For reaction times, at least five repeats are advisable because human reaction time introduces significant random error.

进行重复读数并计算平均值。对于反应时间，建议至少重复五次，因为人类反应时间会引入显著的随机误差。

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5. Recording and Presenting Data | 记录与呈现数据

Data tables must have ruled margins, clear headings with units, and values recorded to the appropriate number of decimal places that reflects the instrument precision.

数据表必须有带边框的列、带单位的明确标题，并且数值记录的小数位数应反映仪器的精密度。

Qualitative observations, such as colour changes or gas evolution, should be recorded in a separate ‘Observations’ column. Use precise language: ‘solution turned milky white’ not ‘went cloudy’.

定性观测（如颜色变化或气体产生）应记录在单独的“观察”列中。使用精准的语言：“溶液变为乳白色”，而不是“变浑浊”。

All data should be recorded in ink and any mistake crossed out with a single line, so the original entry remains legible. Never use correction fluid.

所有数据都应用墨水记录，错误用单线划掉，使原始条目仍清晰可辨。切勿使用修正液。

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6. Processing Data and Calculations | 数据处理与计算

When calculating the mean, exclude anomalous values that lie far outside the range of other repeats. Justify their exclusion in your write‑up, perhaps due to a recorded procedural error.

计算平均值时，排除远超出其他重复值范围的异常数值。在实验报告中说明排除的理由，可能是由于记录下的操作失误。

Carry out calculations such as rates, percentage error, and gradients with careful attention to significant figures. The number of significant figures in your result should match the least precise measurement used in the calculation.

进行速率、百分误差和梯度等计算时，需仔细注意有效数字。结果的有效数字位数应与计算中所用最不精确测量值匹配。

For example, if you measure mass to 0.01 g and volume to 1 cm³, your calculated density should be given to two significant figures, not five.

例如，若质量测量至 0.01 g 而体积测量至 1 cm³，那么计算出的密度应保留两位有效数字，而不是五位。

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7. Plotting Graphs | 绘制图表

In WJEC practical assessments, you will often be asked to plot a line graph. Axes must be labelled with the quantity and unit, and the scale should use at least half the graph paper in each direction, avoiding awkward scales like 3s or 7s.

在 WJEC 实验考核中，你经常需要绘制线形图。坐标轴须标注物理量和单位，且刻度应在每个方向上至少使用坐标纸的一半，避免使用 3、7 这样不方便的刻度。

Plot points with small, neat crosses. Draw a straight line of best fit if the relationship is clearly linear, or a smooth curve if not. Do not join dot‑to‑dot.

用小而整洁的十字标出数据点。若关系明显呈线性，则画出最佳拟合直线；若非如此，则画出平滑曲线。不要逐点相连。

When calculating a gradient, use a large triangle that covers more than half the line, and show your working clearly. The gradient always carries units, such as m s⁻² or Ω m.

计算梯度时，使用覆盖线大半部分的大三角形，并清晰显示运算过程。梯度总是带有单位，如 m s⁻² 或 Ω m。

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8. Drawing Conclusions | 得出结论

Your conclusion must refer directly back to the hypothesis and the data obtained. Use phrases like ‘The results support the hypothesis because …’ and quote specific values from your graph or table.

你的结论必须直接回顾假设和所获数据。使用“结果支持假设，因为……”之类的表述，并引用图表或表格中的具体数值。

Describe the relationship seen: linear, directly proportional, inversely proportional, or a curve that reaches a plateau. Explain the scientific theory behind the trend using your earlier learning.

描述所观察到的关系：线性、正比例、反比例，或是达到平台的曲线。运用先前所学的知识解释趋势背后的科学原理。

If your conclusion does not perfectly match the expected outcome, do not alter the data. Instead, discuss reasons in the evaluation section.

若你的结论与预期结果不完全吻合，不要修改数据，而是在评估部分讨论原因。

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9. Evaluation and Error Analysis | 评估与误差分析

Distinguish between systematic errors, which shift all readings in one direction (e.g. a thermometer reading 98 °C in boiling water), and random errors that cause scatter about the true value.

区分系统误差与随机误差：系统误差使所有读数朝一个方向偏移（例如，温度计在沸水中读数为 98 °C），随机误差则导致数值围绕真值散开。

Identify the largest source of procedural uncertainty in your investigation. For a reaction timing experiment, it is often the start/stop judgment, not the stopwatch resolution.

识别实验中最大的操作不确定性来源。在反应计时实验中，它往往是启动/停止的判断，而非秒表的分辨率。

Calculate percentage uncertainty for key measurements: (uncertainty ÷ measured value) × 100%. Compare this with the percentage difference between your result and the literature value to determine if there is an unresolved systematic error.

计算关键测量的百分不确定度：（不确定度 ÷ 测量值）× 100%。将其与你的结果和文献值之间的百分差异比较，以判断是否存在未解决的系统误差。

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10. Suggesting Improvements and Extensions | 建议改进与拓展

Propose specific refinements to the method, not vague statements like ‘be more careful’. For example, ‘Use a water bath and a thermometer accurate to ±0.1 °C instead of a beaker on a Bunsen burner to maintain a constant temperature.’

提出对方法的具体改进，而非“更小心”之类的笼统说法。例如，“使用水浴和精度为 ±0.1 °C 的温度计，而不用本生灯上的烧杯，以维持恒定温度”。

Suggest how the investigation could be extended to test a related hypothesis, perhaps by changing a different independent variable or applying the same technique to another chemical system.

建议如何拓展该探究以检验一个相关假设，或许是通过更换不同的自变量，或将同一技术应用于另一个化学体系。

State clearly that increasing the number of replicates or taking measurements at a higher resolution would improve the reliability and resolution of the dataset, reducing the effect of random errors.

明确说明增加重复次数或以更高分辨率进行测量将提升数据集的可靠性与分辨率，从而降低随机误差的影响。

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11. Accuracy, Precision, and Reliability | 准确度、精密度与可靠性

Understand the difference: accuracy is how close a measurement is to the true value; precision is how close repeated measurements are to each other. You can have high precision but low accuracy if a systematic error is present.

理解其中的区别：准确度指测量值接近真值的程度；精密度指重复测量值彼此接近的程度。若存在系统误差，则可能精密度高而准确度低。

Reliability refers to the consistency of your data. A reliable set of results will have low spread among repeats, and an investigation is considered reliable if it can be repeated by another scientist with similar results.

可靠性指数据的一致性。一组可靠的结果在重复之间离散程度低；如果一项研究能被另一位科学家重复并得到相似结果，则被认为是可靠的。

Use these terms appropriately in your evaluation to show examiners that you have a rigorous understanding of experimental science.

在评估部分恰当地使用这些术语，向考官展示你对实验科学的严格理解。

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12. Mathematical and Measurement Skills | 数学与测量技能

You must be comfortable converting units (kg to g, cm³ to m³, °C to K) and using standard form for very large or small numbers. For example, the charge of an electron is 1.60 × 10⁻¹⁹ C.

你必须熟练转换单位（kg 转为 g，cm³ 转为 m³，°C 转为 K），并能对极大或极小的数使用科学记数法。例如，电子电荷为 1.60 × 10⁻¹⁹ C。

Practice rearranging equations such as ΔG = ΔH – TΔS, and substituting values correctly. Always show the steps of your calculation to earn method marks, even if the final answer is wrong.

练习重排方程，如 ΔG = ΔH – TΔS，并正确代入数值。始终展示计算步骤，即使最终答案有误，也能获得方法分。

When dealing with logarithms, such as in pH calculations, remember that pH = -log₁₀[H⁺]. A change of one pH unit corresponds to a ten‑fold change in hydrogen ion concentration.

处理类似 pH 计算中的对数时，记住 pH = -log₁₀[H⁺]。pH 值变化一个单位对应氢离子浓度十倍的变化。

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