AQA 9620 CH04 Specimen Paper 2016 Question 2 Walkthrough | 2016年国际A Level化学样卷第2题精讲

📚 AQA 9620 CH04 Specimen Paper 2016 Question 2 Walkthrough | 2016年国际A Level化学样卷第2题精讲

The AQA 9620 CH04 International A Level Chemistry specimen paper is a key resource for understanding the depth of A2 chemistry assessment. Question 2 typically focuses on acid-base equilibria, including weak acid pH, Ka, pKa, buffer solutions, and titration curves. This article breaks down the exact skills needed to answer Question 2 confidently.

AQA 9620 CH04 国际 A Level 化学样卷是理解 A2 化学考查深度的重要资源。第2题通常聚焦酸碱平衡，包括弱酸 pH、Ka、pKa、缓冲溶液和滴定曲线。本文拆解回答第2题所需的核心技能。

1. What Question 2 Assesses | 第2题考查内容

In the 2016 specimen paper, Question 2 is built around a weak acid such as ethanoic acid or a similar organic acid. You must move between Ka, pKa, [H⁺], pH, and concentrations of conjugate base and acid.

在2016年样卷中，第2题围绕弱酸（如乙酸或类似有机酸）展开。你必须能在 Ka、pKa、[H⁺]、pH、共轭碱浓度和酸浓度之间灵活转换。

Examiners often reward clear working, correct units, and sensible significant figures. A final pH should usually be quoted to 2 decimal places, and Ka values to 2 or 3 significant figures.

考官通常奖励清晰的演算步骤、正确的单位和合理的有效数字。最终 pH 通常保留两位小数，Ka 值保留两位或三位有效数字。

2. Extraction of Data | 数据提取

Start by listing every value given: the acid concentration, the value of Ka or pKa, and any added salt or base concentration. Convert all volumes to dm³ and all concentrations to mol dm⁻³ before substituting.

首先列出所有给定数值：酸浓度、Ka 或 pKa 的值，以及任何加入的盐或碱的浓度。在代入公式前，将所有体积换算成 dm³，所有浓度换算成 mol dm⁻³。

If the question gives pKa, convert it immediately using Ka = 10^(−pKa). If it gives Ka, you may need pKa = −log₁₀(Ka).

如果题目给出 pKa，立即用 Ka = 10^(−pKa) 转换。如果给出 Ka，可能需要用 pKa = −log₁₀(Ka)。

pKa = −log₁₀(Ka) and Ka = 10^(−pKa)

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