📚 The pH Scale and Neutralisation | pH值标度与中和反应
Acids and bases are everywhere around us, from the food we eat to the soil where plants grow. Understanding the pH scale and neutralisation reactions is essential for mastering IGCSE chemistry.
酸和碱无处不在，从我们吃的食物到植物生长的土壤。理解pH标度和中和反应是掌握IGCSE化学的关键。
1. Acids and Bases Defined | 酸与碱的定义
In the Edexcel IGCSE specification, an acid is a substance that produces hydrogen ions (H⁺) when dissolved in water. For example, hydrochloric acid (HCl) ionises in water to form H⁺ (aq) and Cl⁻ (aq).
在Edexcel IGCSE考纲中，酸是指溶于水时产生氢离子（H⁺）的物质。例如，盐酸（HCl）在水中电离生成H⁺（aq）和Cl⁻（aq）。
A base is a substance that neutralises an acid to form water. An alkali is a soluble base that produces hydroxide ions (OH⁻) in aqueous solution. Common alkalis include sodium hydroxide (NaOH) and calcium hydroxide (Ca(OH)₂).
碱是能够中和酸并生成水的物质。可溶性碱是溶于水后产生氢氧根离子（OH⁻）的碱。常见的可溶性碱包括氢氧化钠（NaOH）和氢氧化钙（Ca(OH)₂）。
2. The pH Scale | pH标度
The pH scale runs from 0 to 14 and tells us how acidic or alkaline a solution is. A solution with pH 7 is neutral, pH less than 7 is acidic, and pH greater than 7 is alkaline. The lower the pH, the more acidic the solution.
pH标度从0到14，表示溶液的酸性或碱性。pH=7为中性，pH小于7为酸性，pH大于7为碱性。pH值越低，酸性越强。
Each whole pH unit represents a tenfold change in hydrogen-ion concentration. Therefore, a solution of pH 3 is ten times more acidic than one of pH 4, and one hundred times more acidic than pH 5.
每个整数pH单位对应氢离子浓度变化10倍。
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