📚 Graphing Skills for AQA A Level Chemistry | AQA A Level 化学绘图技能
Graphs are not just pictures of data. In AQA A Level Chemistry, they are quantitative tools for finding rates, orders of reaction, activation energies, equivalence points, and unknown concentrations. This article summarises the graphing techniques and interpretations that examiners expect.
图表不仅仅是数据的图像。在 AQA A Level 化学中，它们是用于求算反应速率、反应级数、活化能、等当点和未知浓度的定量工具。本文总结考官期望掌握的绘图技能和对图形的解读。
1. Axes, Variables and Labels | 坐标轴、变量与标注
Always put the independent variable on the x-axis and the dependent variable on the y-axis. In kinetics, time is usually the independent variable for concentration-time graphs, so time goes on the x-axis and concentration on the y-axis.
始终将自变量放在 x 轴，将因变量放在 y 轴。在动力学中，时间通常是浓度-时间图的自变量，因此时间在 x 轴，浓度在 y 轴。
Label each axis with the quantity and its unit in brackets, for example: 'Concentration / mol dm⁻³' or 'Time / s'. AQA requires both a descriptive label and a unit. Use a linear scale unless told otherwise.
每个坐标轴都应标注物理量及单位（放在括号中），例如：“Concentration / mol dm⁻³”或“Time / s”。AQA 要求同时有描述性标签和单位。除非另有说明，否则使用线性刻度。
In rate experiments, possible dependent variables include concentration, absorbance, pH, gas volume, or mass loss. The independent variable might be time, concentration, temperature, or volume of titrant added. Choosing the correct axes is the first step in any graphical analysis.
在速率实验中，可能的因变量包括浓度、吸光度、pH、气体体积或质量损失。自变量可以是时间、浓度、温度或加入滴定剂的体积。选择正确的坐标轴是任何图形分析的第一步。
2. Choosing Sensible Scales | 选择合理的刻度
The scale should make your plotted points cover more than half of the graph paper in both directions. Do not start every axis at zero if your data are all large; for example, a temperature axis from 20 to 60 °C can start at 20 °C as long as the scale is clear.
刻度应使你标出的数据点在两个方向上都占据方格纸的一半以上。并非所有坐标轴都必须从零开始；例如 20 到 60 °C 的温度轴可以从 20 °C 开始，只要刻度清晰即可。
Use simple intervals such as 1, 2, 5 or 10 units per square. Avoid intervals like 3, 7 or 0.3 because they make plotting and interpolation difficult. If you use a false origin, mark it clearly with a zigzag or break on the axis.
每个小格使用简单的间隔，如 1、2、5 或 10 个单位。避免 3、7 或 0.3 这类间隔，因为它们会给描点和插值带来困难。若使用非零起点，需在轴上用锯齿或断点清楚标出。
A well-chosen scale also makes it easier to read gradients and intercepts. If the scale is too small, gradients become difficult to determine accurately; if it is too large, points may not fit on the grid. Always plot the graph in pencil first so corrections can be made cleanly.
合理的刻度也会使斜率和截距的读取更容易。如果刻度太小，斜率就难以准确确定；如果太大，数据点可能无法落在方格内。画图时应先用铅笔绘图，以便干净地修改。
3. Plotting Data Points and Drawing Lines | 描画数据点与绘制线条
or circled dots, not large blobs. The centre of each cross must lie exactly at the coordinates. Do not join point-to-point with a ruler unless the relationship is known to be strictly linear.
数据点用小而清晰的叉号（×）或带圈圆点标出，不要画成大黑点。每个叉的中心必须准确落在坐标上。除非已知关系严格为线性，否则不要用直尺逐点连接。
Draw a best-fit straight line or smooth curve that passes through or near all points. For a straight line, use a transparent ruler and balance the points on both sides of the line, ignoring obvious outliers. For a curve, draw one smooth continuous curve, not a series of short straight segments.
绘制最佳拟合直线或光滑曲线，使其经过或接近所有数据点。画直线时使用透明直尺，让点尽量均匀分布在直线两侧，忽略明显的异常点。画曲线时应绘制一条光滑连续的曲线，而不是一系列短直线段。
If a point lies far from the general trend and you have a reason to suspect an experimental error, mark it as anomalous and exclude it from the best-fit line. In AQA practical write-ups, you should always state which point you excluded and why.
如果某个点远离总体趋势，并且你有理由怀疑存在实验误差，就将其标记为异常点，并在拟合直线时排除它。在 AQA 实验报告中，你应始终说明排除了哪个点以及为什么。
4. Gradients, Tangents and Rates | 斜率、切线与速率
line touching the curve at the chosen point, extend it, and calculate gradient = Δy ÷ Δx.
某一时刻的反应速率等于该时刻浓度-时间曲线上切线的斜率。在所选取的点处画出与曲线相切的直线，延长后计算斜率 = Δy ÷ Δx。
For a straight line, choose two well-separated points on the line, not necessarily data points. Calculate gradient using the formula:
对于直线，选择线上相距较远的两个点，而不一定是实验数据点。使用公式计算斜率：
gradient = (y₂ − y₁) / (x₂ − x₁)
Always include units for the gradient, for example mol dm⁻³ s⁻¹ if the y-axis is concentration in mol dm⁻³ and the x-axis is time in seconds. A negative gradient on a concentration-time graph shows the reactant is being used up.
斜率始终要写明单位。例如，若 y 轴是浓度（mol dm⁻³）、x 轴是时间（s），则速率单位为 mol dm⁻³ s⁻¹。浓度-时间
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