IGCSE OCR Chemistry: pH Calculations – Essential Exam Concepts | IGCSE OCR 化学：pH计算 考点精讲

📚 IGCSE OCR Chemistry: pH Calculations – Essential Exam Concepts | IGCSE OCR 化学：pH计算 考点精讲

pH calculations are a fundamental aspect of the IGCSE OCR Chemistry syllabus. Mastering these calculations not only helps you solve numerical problems but also deepens your understanding of acid–base chemistry. This guide covers all key concepts required for the exam, from the definition of pH to working with the ionic product of water, Kw, for strong acids and alkalis.

pH计算是IGCSE OCR化学大纲的核心内容。掌握这些计算不仅能帮你解决数值问题，还能加深你对酸碱化学的理解。本指南涵盖考试所需的所有关键概念，从pH的定义到运用水的离子积Kw计算强酸和强碱的pH。

1. What is pH and Why Does It Matter? | 什么是pH及其重要性？

pH is a measure of the concentration of hydrogen ions, [H⁺], in a solution. It indicates whether a solution is acidic, alkaline, or neutral. The term ‘pH’ stands for ‘potential of hydrogen’ or ‘power of hydrogen.’ Understanding pH is essential for predicting the behaviour of acids and bases during chemical reactions and in real-world contexts such as soil acidity and biological systems.

pH是溶液中氢离子浓度[H⁺]的量度。它表示溶液是酸性、碱性还是中性。术语“pH”代表“氢的潜力”或“氢的指数”。理解pH对于预测酸碱在化学反应中的行为以及在实际场景中（如土壤酸度和生物系统）的应用至关重要。

For IGCSE OCR, you must be able to define pH, explain its relationship with hydrogen ion concentration, and perform calculations involving strong acids and alkalis using the equations provided.

对于IGCSE OCR，你必须能够定义pH、解释它与氢离子浓度的关系，并使用给定公式进行涉及强酸和强碱的计算。

2. Understanding the pH Scale | 理解pH标度

The pH scale ranges from 0 to 14 under standard conditions (25 °C). A pH less than 7 indicates an acidic solution (higher [H⁺]), a pH of 7 is neutral (pure water), and a pH greater than 7 indicates an alkaline solution (lower [H⁺]). Each unit decrease in pH represents a tenfold increase in [H⁺].

pH标度在标准条件下（25 °C）范围为0到14。pH小于7表示酸性溶液（[H⁺]较高），pH等于7为中性（纯水），pH大于7表示碱性溶液（[H⁺]较低）。pH每降低一个单位，[H⁺]就增加十倍。

This logarithmic scale means that small changes in pH correspond to large changes in acidity. For example, a solution with pH 3 has 10 times more hydrogen ions than one with pH 4, and 100 times more than pH 5.

这种对数标度意味着pH的微小变化对应着酸度的巨大变化。例如，pH为3的溶液中氢离子浓度是pH为4的溶液的10倍，是pH为5的溶液的100倍。

3. The pH Formula: pH = –log₁₀[H⁺] | pH公式：pH = –log₁₀[H⁺]

The key equation for pH is:

pH的关键方程是：

pH = –log₁₀[H⁺]

Here, [H⁺] is the hydrogen ion concentration in mol dm⁻³. The logarithm is to the base 10. To convert pH back to [H⁺], you use:

其中，[H⁺]是以mol dm⁻³为单位的氢离子浓度。对数是取以10为底的对数。要将pH转回[H⁺]，使用：

[H⁺] = 10⁻ᵖᴴ mol dm⁻³

You must be comfortable using these equations in both directions. Practise taking logs and antilogs using your calculator.

你必须能够熟练地双向使用这些方程。练习使用计算器求对数和反对数。

4. Calculating pH of Strong Acids | 计算强酸的pH

For a strong monoprotic acid like HCl or HNO₃, it fully dissociates in water, so [H⁺] equals the concentration of the acid. For example, a 0.1 mol dm⁻³ HCl solution has [H⁺] = 0.1 mol dm⁻³. The pH is then calculated as:

对于像HCl或HNO

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