📚 AS AQA Chemistry Unit 3: Practical Skills and Data Interpretation | AS AQA 化学第三单元：实验技能与数据分析
The June 2019 insert for AQA AS Chemistry Unit 3 required students to apply practical techniques to real experimental data. This revision guide focuses on the core skills that are consistently tested: analysing procedures, titrations, enthalpy changes, rates, organic tests, graph work and mole calculations.
AQA AS 化学第三单元2019年6月插页要求学生将实验技术应用于真实实验数据。本复习指南聚焦于反复考查的核心技能：分析步骤、滴定、焓变、速率、有机检验、作图与摩尔计算。
1. Understanding the Insert | 理解考试插页
The insert is not a set of answers but a source of experimental context. You must be able to locate the independent variable, dependent variable and control variables in the method. For a typical rate experiment, the temperature is independent, the time for a fixed volume of gas is dependent, and the mass of marble chips is controlled.
插页不是答案，而是实验背景的来源。你必须能从方法中找出自变量、因变量和控制变量。在一个典型速率实验中，温度是自变量，产生固定体积气体的时间是因变量，大理石碎片的质量是控制变量。
In the June 2019 insert, candidates saw a table of titration results with a ‘rough’ reading. The rough reading should not be used when calculating the mean. The three concordant readings are averaged, and any outlier is rejected.
在2019年6月插页中，考生看到一张带“粗略”读数的滴定结果表。计算平均值时不应使用粗略读数。三个平行读数被取平均，任何离群值应被剔除。
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Always check whether the burette readings are in cm³ and convert to dm³ when doing mol calculations.
始终检查滴定管读数是否以 cm³ 为单位，并在进行摩尔计算时转换为 dm³。
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Use the units shown in the table to decide whether volumes are recorded to 0.05 cm³ precision.
使用表格中显示的单位来判断体积是否记录到 0.05 cm³ 的精度。
2. Experimental Design and Variables | 实验设计与变量
A well-designed experiment in a Unit 3 insert will include a clear method, controlled variables and repeated measurements. To answer questions on experimental design, identify what is being changed and what is being measured. Temperature, concentration and surface area are common independent variables in AS chemistry.
第三单元插页中的良好实验设计会包含清晰的方法、控制变量和重复测量。回答实验设计问题时，要确定什么在改变、什么在测量。温度、浓度和表面积是AS化学中常见的自变量。
Controls ensure that only the independent variable affects the result. For example, in an acid–carbonate rate experiment, the total volume of acid, the mass of carbonate and the particle size must be kept the same to allow a fair comparison.
控制变量确保只有自变量影响结果。例如，在酸–碳酸盐速率实验中，酸的总体积、碳酸盐的质量和颗粒大小必须保持一致，才能进行公平比较。
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State control variables explicitly: same thermometer, same container, same total volume.
明确说明控制变量：同一支温度计、同一个容器、相同总体积。
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Repeats are needed to calculate a mean and to identify anomalies.
重复实验是为了计算平均值并识别异常值。
3. Titration Core Technique | 滴定核心技术
Titration appears in nearly every Unit 3 paper. You need to know the practical order: rinse the burette with the solution it will contain, fill it, remove the air jet, take the initial reading, add the titrant until the indicator changes colour, and record the final reading. The endpoint should be a sharp colour change.
滴定几乎出现在每一份第三单元试卷中。你需要知道操作顺序：用待装液润洗滴定管、装液、排空气泡、读取初始读数、滴加滴定液直到指示剂变色、记录终点读数。终点应当是明显的颜色变化。
In the 2019 insert, hydrochloric acid was titrated against sodium hydroxide. The key equation is:
HCl + NaOH → NaCl + H₂O
The amount of NaOH in a 25.0 cm³ portion can be calculated using the concentration and volume:
n(NaOH) = c × V = 0.100 mol dm⁻³ × 0.0250 dm³ = 2.50 × 10⁻³ mol
Because the reaction ratio is 1 : 1, this is also the amount of HCl in the average titre. If the average titre is 20.00 cm³, the HCl concentration is:
c(HCl) = n / V = 2.50 × 10⁻³ mol / 0.02000 dm³ = 0.125 mol dm⁻³
因为反应摩尔比为1:1，这也是平均滴定体积中HCl的物质的量。若平均滴定体积为20.00 cm³，则HCl浓度为：
c(HCl) = n / V = 2.50 × 10⁻³ mol / 0.02000 dm³ = 0.125 mol dm⁻³
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Show the mole ratio clearly; many candidates lose marks by forgetting to write the equation.
清晰写出摩尔比；许多考生因忘记写方程式而丢分。
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Use concordant results within 0.10 cm³ of each other for the mean.
取彼此相差不超过0.10 cm³的平行结果计算平均值。
4. Enthalpy Measurements | 焓变测量
Enthalpy experiments in the Unit 3 insert often involve a neutralisation or solution reaction. The temperature change is measured, and the heat change is calculated using q = m c ΔT. The specific heat capacity of water is usually taken as 4.18 J g⁻¹ K⁻¹.
第三单元插页中的焓变实验通常涉及中和或溶解反应。测量温度变化，并用 q = m c ΔT 计算热量变化。水的比热容通常取4.18 J g⁻¹ K⁻¹。
For neutralising 50.0 cm³ of 1.00 mol dm⁻³ HCl with 50.0 cm³ of 1.00 mol dm⁻³ NaOH, the mass of solution is about 100 g. If the temperature rises by 6.5 K, then:
q = 100 g × 4.18 J g⁻¹ K⁻¹ × 6.5 K = 2717 J = 2.72 kJ
The number of moles of water formed is 0.0500 mol, because the 50.0 cm³ of 1.00 mol dm⁻³ HCl contains 0.0500 mol of H⁺. The enthalpy change is:
ΔH = −q / n = −2.72 kJ / 0.0500 mol = −54.4 kJ mol⁻¹
The negative sign shows the reaction is exothermic.
当中和50.0 cm³ 1.00 mol dm⁻³ HCl 与50.0 cm³ 1.00 mol dm⁻³ NaOH时，溶液质量约为100 g。若温度升高6.5 K，则：
q = 100 g × 4.18 J g⁻¹ K⁻¹ × 6.5 K = 2717 J = 2.72 kJ
生成水的物质的量为0.0500 mol，因为50.0 cm³ 1.00 mol dm⁻³ HCl中含有0.0500 mol H⁺。焓变为：
ΔH = −q / n = −2.72 kJ / 0.0500 mol = −54.4 kJ mol⁻¹
负号表示反应放热。
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Assume the density of all dilute aqueous solutions is 1.00 g cm⁻³.
假设所有稀水溶液的密度为1.00 g cm⁻³。
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Do not forget to convert J to kJ when quoting ΔH in kJ mol⁻¹.
在将ΔH以kJ mol⁻¹表示时，不要忘记将J转换为kJ。
5. Rates of Reaction | 反应速率
Rates can be followed by measuring gas volume, loss of mass, colour change or turbidity. In a Unit 3 insert, data may be presented as a table of volume of gas against time. You should be able to calculate an initial rate by drawing a tangent at time zero and finding the gradient.
速率可通过测量气体体积、质量损失、颜色变化或浊度来追踪。在第三单元插页中，数据可能以气体体积随时间变化的表格形式给出。你应当能够通过在零时刻画切线并计算斜率来得到初始速率。
For example, if 0.00 cm³ of gas is collected at t = 0 s and 18.0 cm³ at t = 20 s on the tangent line, the initial rate is:
rate = ΔV / Δt = 18.0 cm³ / 20 s = 0.90 cm³ s⁻¹
Alternatively, if concentration is measured, the unit becomes mol dm⁻³ s⁻¹. The insert may ask you to predict how increasing temperature changes the rate using collision theory: particles move faster, collide more frequently, and a greater proportion have energy ≥ activation energy.
例如，若切线上 t = 0 s 时收集气体0.00 cm³，t = 20 s 时收集气体18.0 cm³，则初始速率为：
rate = ΔV / Δt = 18.0 cm³ / 20 s = 0.90 cm³ s⁻¹
或者，若测量浓度，则单位为 mol dm⁻³ s⁻¹。插页可能要求你利用碰撞理论预测升温如何改变速率：粒子运动更快、碰撞更频繁，并且更多粒子具有 ≥ 活化能的能量。
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Choose a tangent with a large rise and run to reduce reading error.
选择跨距较大的切线来减小读数误差。
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Monitors the same variable throughout: volume, concentration, absorbance.
始终监测同一变量：体积、浓度、吸光度。
6. Organic Functional Group Tests | 有机官能团检验
Unit 3 inserts often include simple test-tube reactions to identify organic compounds. In the AS AQA specification, you must know tests for alkenes, alcohols and halogenoalkanes.
第三单元插页常包含简单的试管反应来鉴别有机化合物。在AS AQA考纲中，你必须知道烯烃、醇和卤代烷的检验方法。
Alkenes are identified by adding bromine water: the orange colour is decolourised because addition occurs across the C=C bond. Primary and secondary alcohols are oxidised by acidified potassium dichromate(VI), turning the orange solution green. Tertiary alcohols do not react. Halogenoalkanes can be identified by warming with aqueous sodium hydroxide, then acidifying with nitric acid and adding silver nitrate solution.
烯烃的鉴别方法是加入溴水：橙色褪去，因为加成反应发生在C=C键上。伯醇和仲醇能被酸化的重铬酸钾(VI)氧化，使橙色溶液变为绿色。叔醇不发生反应。卤代烷可先与氢氧化钠水溶液加热，再酸化并加入硝酸银溶液来鉴别。
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The silver halide precipitate confirms the halogen: AgCl white, AgBr cream, AgI yellow.
卤化银沉淀确认卤素：AgCl白色、AgBr奶油色、AgI黄色。
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Bromine water must be orange before the test; if it stays orange, the compound is not an alkene.
溴水在测试前必须是橙色；若仍为橙色，则该化合物不是烯烃。
7. Infrared and Mass Spectrometry | 红外光谱与质谱
The insert may ask you to interpret an infrared spectrum. Before AS, you need to know that O–H absorbs broadly around 3200–3600 cm⁻¹ and C=O absorbs sharply around 1700 cm⁻¹. A carboxylic acid shows both a broad O–H and a C=O peak.
插页可能要求你解读红外光谱。在AS阶段，你需要知道O–H在3200–3600 cm⁻¹区域有宽峰，C=O在1700 cm⁻¹附近有尖峰。羧酸同时显示宽O–H峰和C=O峰。
Mass spectrometry can give the relative molecular mass from the molecular ion peak, M⁺. For example, if the M⁺ peak is at m/z = 46 for an alcohol, the Mr is 46, which corresponds to ethanol, C₂H₅OH. Fragmentation peaks can help identify the structure.
质谱可以从分子离子峰M⁺给出相对分子质量。例如，某醇的M⁺峰位于 m/z = 46，则Mr为46，对应乙醇C₂H₅OH。碎片峰有助于推断结构。
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Use the molecular ion peak to find Mr, not the base peak.
使用分子离子峰而非基峰来确定Mr。
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Do not confuse absorption due to C–H; it appears near 2900 cm⁻¹.
不要将C–H吸收峰混淆；它出现在2900 cm⁻¹附近。
8. Data Handling and Graph Skills | 数据处理与图表技能
Graphs in the insert may show a curve of volume against time, temperature against time, or a calibration curve. You must draw the line of best fit, label axes with units, and report the gradient with correct units.
插页中的图表可能显示体积–时间曲线、温度–时间曲线或校准曲线。你必须画出最佳拟合线、标注坐标轴单位，并以正确单位报告斜率。
When using graphs to find a rate, choose two points on the best-fit line, not data points. For a concentration-time graph, the instantaneous rate at any time is the gradient of the tangent. For a linear graph, the gradient is constant.
利用图表求速率时，应选择最佳拟合线上的两个点，而不是原始数据点。对于浓度–时间图，任一时刻的瞬时速率就是切线的斜率。对于线性图，斜率为常数。
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Include the origin if the relationship starts at zero, but do not force the line through the origin if data clearly disproves it.
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