Edexcel化学 GCSE 酸碱 强酸弱酸 pH 滴定
酸碱这一章在 Edexcel GCSE 化学（1CH0）里属于 Topic 3 Chemical changes 的 Acids and bases 部分，spec 编号 3.1 到 3.14，Paper 1 的考试时间是 1 小时 45 分钟、满分 100 分、占总成绩的一半，两张卷子都用同一份 spec 条目。很多学生复习这一章只背反应式，记住盐酸生成氯化物、硫酸生成硫酸盐这几条，遇到强弱酸比较、pH 曲线或者滴定计算就写不出理由。真正拉开差距的是三组容易混的对比：强酸与弱酸、浓与稀、三种制盐路线各自的适用条件。下面十二节按对比排开，每一节都给出一条能直接落到卷面上的说法，并标出学生在这类题上最常丢的分。文中提到的卷面结构、核心实验编号与 spec 条目都按 Pearson 官方 spec（Issue 4）和 Core practical guide（2016 版）核对过，考试年份按 2018 年 5 月首次考试的口径写。
Acids and bases sit inside Topic 3 Chemical changes of the Edexcel GCSE Chemistry specification (1CH0), numbered 3.1 to 3.14, and Paper 1 runs for 1 hour 45 minutes for 100 marks, half of the qualification. Candidates who revise by memorising equations alone usually stall on comparisons of acid strength, pH curves and titration arithmetic, because those items ask for reasons rather than products. The twelve sections below are arranged as comparisons, each ending on a wording that earns marks in the exam hall; the paper structure, core practical numbers and specification references follow the Pearson specification (Issue 4) and the 2016 Core practical guide, with first assessment in May 2018.
酸碱的离子定义 / Acids, bases and alkalis defined by ions
酸是在水溶液中能给出氢离子 H+ 的物质，碱是能中和酸的物质，可溶于水的碱叫碱液 alkali，它在水里给出氢氧根离子 OH-。判断一种物质属于哪一类看的是它在水里的行为，不是它常温下是固体还是液体，氧化铜是不溶于水的碱，氢氧化钠是可溶的碱，两者都能和酸反应。学生最常把碱和碱液当成同义词，写成"碱一定是碱金属氢氧化物"就丢分，因为氧化镁、碳酸钠同样属于碱这一类。Edexcel 的 Acids and bases 部分（3.1 到 3.14）把酸定义为在水溶液中产生 H+ 的物质，后面所有的解释题都从这一句出发。反应里真正起作用的是离子，盐酸和硫酸溶液中的 H+ 才是让 pH 降到 7 以下的那个粒子。写解释题时要把"在水中"三个字带上，因为纯的氯化氢气体不算酸，只有溶于水之后才电离，导电性也是靠溶液里自由移动的离子。
An acid is a substance that releases hydrogen ions in aqueous solution, while a base neutralises an acid and an alkali is simply a base that dissolves in water and gives hydroxide ions. Copper oxide is a base that does not dissolve and sodium hydroxide is an alkali, yet both react with acid, so the label depends on behaviour in water rather than on the state of the substance. Candidates often write that every alkali is a metal hydroxide, which ignores metal oxides and carbonates, and pure hydrogen chloride gas is not an acid until it dissolves.
pH 标度与十倍规则 / The pH scale and the ten-fold rule for H+
pH 标度从 0 到 14，7 是中性，数值越小酸性越强，数值越大碱性越强。Edexcel spec 的 Acids and bases 部分写明 pH 每改变 1 个单位，氢离子浓度变化十倍，所以 pH 4 的溶液里 H+ 浓度是 pH 6 的一百倍。这条规则常被拿来做选择题，问一个溶液比另一个酸多少倍，答案要和 pH 之差对应的十的幂对上。很多学生以为 pH 是线性刻度，写"pH 2 是 pH 4 的两倍酸"就错了，正确的说法是一百倍。指示剂只能给出粗略范围，石蕊从红到蓝，通用指示剂能分辨到大约 1 个 pH 单位，要精确到小数点后一位就得用 pH 探头。卷子上如果给了 pH 曲线图，横轴一般是加入的碱的体积或固体勺数，纵轴是 pH，读数要按小格估到半个格的精度。
The pH scale runs from 0 to 14 with 7 neutral, and the Edexcel specification states that a change of one pH unit corresponds to a ten-fold change in hydrogen ion concentration, so pH 4 holds one hundred times more H+ than pH 6. Multiple-choice items exploit this by asking how many times more acidic one solution is, and the answer has to match the power of ten implied by the gap in pH units. Universal indicator resolves about one pH unit while a pH probe gives readings to one decimal place, and graph questions ask for values estimated to half a small square.
强酸与弱酸：完全电离与部分电离 / Strong and weak acids: full and partial ionisation
强弱说的是电离程度，不是浓度。盐酸、硫酸、硝酸在水里完全电离，写成 HCl -> H+ + Cl- 时配单向箭头；乙酸、柠檬酸、碳酸只部分电离，CH3COOH 写成 CH3COO- 和 H+ 时要配可逆符号。同样浓度的盐酸和乙酸相比，盐酸的 pH 更低，因为溶液里的 H+ 多。反应速率也不一样，等浓度等体积的两种酸分别和镁条反应，盐酸那边气泡更快，原因还是 H+ 浓度高。学生最常把弱酸理解成稀释过的酸，答题时把 strong 和 concentrated 互换使用，这类解释题几乎每年都出现。中和同体积同浓度的强酸与弱酸，消耗的碱体积相同，因为中和只看酸能提供的 H+ 总量，和电离程度无关，弱酸的电离平衡会随着 H+ 被消耗而向右移动。
Strength describes how completely an acid ionises in water rather than how concentrated the solution is; hydrochloric, sulfuric and nitric acids ionise fully, while ethanoic, citric and carbonic acids ionise only partially. At equal concentration the strong acid gives the lower pH and fizzes faster with magnesium, since more hydrogen ions sit in the same volume. What candidates miss every year is that equal volumes of strong and weak acid at the same concentration need the same volume of alkali, because neutralisation depends on the total amount of acid and the weak acid equilibrium simply shifts as H+ is consumed.
浓与稀和强与弱是两回事 / Concentrated is not the same as strong
浓度说的是每单位体积里溶质的多少，强弱说的是溶质电离的难易，两者可以自由组合。浓乙酸这类浓的弱酸 pH 可以低到 2 到 3，0.01 mol dm-3 的盐酸属于稀的强酸，pH 正好是 2，两个例子在卷面上都会出现。强酸稀释十倍，pH 上升 1 个单位，弱酸稀释十倍，pH 上升不到 1 个单位，原因是稀释让电离平衡向右移动，补回一部分 H+。这个差别在 pH 曲线上表现为弱酸的起点更高、陡峭段更短并且更靠右。很多学生把 mol dm-3 的数值大小当成强弱证据，看到浓盐酸就写强电解质，看到稀乙酸就写弱电解质，两个判断其实一个说浓度，一个说种类。答题时把种类和浓度分两句写，先写强酸还是弱酸，再写稀还是浓，混在一句里最容易被阅卷判成概念不清。
Concentration counts solute per unit volume while strength describes how readily that solute ionises, and the two vary independently; a concentrated weak acid such as ethanoic acid can sit near pH 2, and a dilute strong acid such as 0.01 mol dm-3 hydrochloric acid also sits at pH 2. Diluting a strong acid ten times raises the pH by one unit, whereas a weak acid moves by less than one unit because the equilibrium shifts to replace part of the lost ions. On a pH curve this appears as a higher starting point and a shorter steep section further along the axis.
四种酸反应的对比 / The four acid reaction patterns compared
稀酸能和金属、金属氧化物、金属氢氧化物、金属碳酸盐四类物质反应，产物各不相同。金属加酸生成盐和氢气，现象是气泡，用点燃的木条靠近能听到爆鸣声。氧化铜加硫酸生成硫酸铜和水，固体逐渐溶解，溶液呈蓝色。氢氧化物加酸生成盐和水，没有气体放出，这一条在中和题里考得最多。碳酸盐加酸生成盐、水和二氧化碳，气体通入石灰水变浑浊，这是鉴别碳酸根的常规做法，也是 Pearson 核心实验清单里"鉴别未知盐中的离子"用到的一步。四条反应里只有金属那条会放出氢气，所以题目一提到气体，先想是不是金属和酸。
Dilute acids react with metals, metal oxides, metal hydroxides and metal carbonates, and the products separate these four families; a metal gives a salt and hydrogen, an oxide gives a salt and water, a hydroxide gives a salt and water, and a carbonate gives a salt, water and carbon dioxide. Copper oxide dissolving in sulfuric acid produces a blue solution of copper sulfate, while carbon dioxide turns limewater milky, the same test used in the Pearson core practical on identifying ions in unknown salts. Only the metal route releases hydrogen, so a question that mentions a gas is usually describing a metal and an acid.
中和与离子方程式 / Neutralisation and the ionic equation
中和是酸里的 H+ 和碱里的 OH- 结合成水，离子方程式写成 H+ + OH- -> H2O，这条式子对所有强酸强碱的组合都成立，不管用的是盐酸、硝酸还是硫酸。完整的化学方程式还要写出旁观离子组成的盐，比如 HCl + NaOH -> NaCl + H2O。Edexcel 的 Higher tier 卷在离子方程式上要求更细，会让学生自己写出净离子反应并从两边划掉旁观离子 spectator ions。中和放热，温度计读数上升是反应发生过的直接证据，这一条常和能量变化一起考。学生最常把中和理解成"把酸变成水"，写解释时漏掉留在溶液里的盐，答题就少一个给分点。中和之后溶液不一定中性，反应物有一方过量时 pH 仍偏向另一边，题目给了体积和浓度就先算物质的量再判断。
Neutralisation happens when hydrogen ions from the acid meet hydroxide ions from the alkali to form water, and the ionic equation H+ + OH- -> H2O holds for every strong acid and strong alkali pair. The full equation also shows the salt that stays dissolved, so HCl + NaOH -> NaCl + H2O is the acid-alkali case, and Higher tier papers ask candidates to cancel the spectator ions themselves. The reaction is exothermic, which is why a temperature rise counts as evidence, and a mixture after neutralisation is not automatically neutral when one reactant is in excess.
盐的名字由酸决定 / Naming the salt from the acid used
盐的名字跟着酸走，与金属无关，盐酸一律生成氯化物，硫酸一律生成硫酸盐，硝酸一律生成硝酸盐。锌和硝酸反应得到硝酸锌和氢气，氧化镁和硫酸反应得到硫酸镁和水，两条反应里换的只是金属，盐的尾巴没有变。命名时还要看金属的化合价，铁有两种常见价态，铁和盐酸生成氯化亚铁，氧化铁和盐酸生成氯化铁，这一组对比常在改错题里出现。碳酸盐和酸反应放出二氧化碳的同时也有盐生成，写方程式时两边都要配平。学生最常把硫酸铜写成硫化铜，把酸根的名字和第二种元素混起来，阅卷时这类错误不给分。稳一点的做法是先把酸根名字写出来，再补上金属名，顺序反过来更容易写错。
Salt names follow the acid rather than the metal; hydrochloric acid always gives a chloride, sulfuric acid a sulfate and nitric acid a nitrate. Zinc with nitric acid gives zinc nitrate and hydrogen, magnesium oxide with sulfuric acid gives magnesium sulfate and water, and only the metal part changes between the two. Iron has two common oxidation states, so iron with hydrochloric acid gives iron(II) chloride while iron(III) oxide gives iron(III) chloride, a pair that mark schemes treat as a standard naming error.
三种制盐路线对比 / Three routes to a salt compared
制盐有三条路，用金属或可溶的碱直接反应、用不溶的碱或碳酸盐过量反应再加过滤、用滴定法。金属那条路只适合不太活泼的金属与稀酸，产物和过量的金属不容易分开，所以课堂上很少用它拿晶体。不溶的碱走的是过量加过滤，把氧化铜加到温热的稀硫酸里直到有固体沉在底部不再溶解，说明酸已经用完，然后滤掉多余的氧化铜，得到蓝色硫酸铜溶液。滴定法用于可溶的酸和可溶的碱，用指示剂找到终点，把两种溶液按准确体积混合，再蒸发得到晶体。三条路的关键差别在怎么保证反应物刚好用完，过量固体靠过滤解决，滴定靠体积读数解决。选路线时先看酸和碱是否可溶，再看题目要的是晶体还是溶液。
There are three practical routes: reacting the acid with a metal or a soluble alkali, adding an insoluble base or carbonate in excess and filtering, or running a titration. Copper oxide added to warm dilute sulfuric acid until solid settles at the bottom guarantees that the acid has been used up, and filtration removes the excess before evaporation gives blue crystals of copper sulfate. Titration suits soluble acids and alkalis, where an indicator marks the end point and the two volumes are mixed exactly, so the routes differ mainly in how the reactants are balanced.
核心实验对比：pH 变化与硫酸铜制备 / Core practicals compared: pH change and copper sulfate
Pearson 的 Core practical guide（2016 版）在化学部分列出的核心实验里，与酸碱直接相关的有三个，编号 3.6 的 pH 变化实验、3.17 的硫酸铜制备实验，以及 5.9C 的酸碱滴定。3.6 的做法是先量 25 cm3 稀盐酸放进锥形瓶，每次加一勺氧化钙，搅拌后测 pH，横轴放固体的勺数，纵轴放 pH 读数。这条曲线先是缓慢上升，接近完全中和时出现一段几乎垂直的上升，再加固体 pH 也变化不大，题目问的通常是垂直段出现的位置。3.17 的成败取决于蒸发程度，加热到溶液表面出现结晶膜就停火，冷却后析出蓝色晶体，蒸得太干只会得到粉末。3.6 问的是曲线拐点对应的固体量，3.17 问的是为什么要把氧化铜加过量，两个实验的解释方向完全不同。
The Pearson Core practical guide of 2016 lists three chemistry practicals tied to this topic, numbered 3.6 on pH change, 3.17 on preparing copper sulfate and 5.9C on acid-alkali titration. Practical 3.6 adds spatulas of calcium oxide to a fixed 25 cm3 of dilute hydrochloric acid, records the pH after each addition and plots pH against the number of spatulas, producing a curve with an almost vertical section near the neutral point. Practical 3.17 stops heating once a film of crystals appears at the surface, since evaporating to dryness leaves a powder instead of blue crystals, and the explanation asked for is why the copper oxide is added in excess.
滴定读数与一致性 / Titration readings and concordance
滴定要取准确的碱体积，用移液管配洗耳球量 25.0 cm3 放进锥形瓶，瓶下垫白瓷板方便看颜色变化。滴定管先用酸润洗，装液时用漏斗，读数前把漏斗拿走，读弯月面最低处，视线与刻度齐平。先做一次粗略滴定快速找到大致终点，再加指示剂重新装液，第二次开始逐滴加入，接近终点时半滴半滴地加。评分方案通常把两次相差不超过 0.10 cm3 的结果算作一致，取一致结果的体积用于计算。用掉的体积是末读减初读，记录到小数点后两位，比如 23.45 cm3。学生最常把初读和末读记反，或者在装液时留下气泡，气泡会让读出的体积比实际用掉的酸多。指示剂选甲基橙或酚酞都可以，酚酞在碱里粉红、到终点变无色，方向记反了就会把终点判在后面。
Titrations need an accurate volume of alkali, so a pipette and filler deliver 25.0 cm3 into a conical flask standing on a white tile that makes the colour change easier to see. The burette is rinsed with acid, filled through a funnel that is removed before reading, and read at the bottom of the meniscus with the eye level with the graduation. Mark schemes usually treat two readings within 0.10 cm3 as concordant and use that volume in the calculation, so the reading is recorded to two decimal places such as 23.45 cm3.
滴定计算：浓度、摩尔与体积 / Titration arithmetic
滴定计算走三步，先算已知溶液的物质的量，再按方程式系数比换成待求物质的量，最后除以体积得到浓度。举例来说，25.0 cm3 氢氧化钠溶液用去 0.100 mol dm-3 盐酸 24.50 cm3 到达终点，酸的物质的量是 0.100 乘以 24.50 再除以 1000，等于 0.00245 mol，方程式 HCl + NaOH -> NaCl + H2O 的系数比是 1 比 1，碱也是 0.00245 mol，浓度等于 0.00245 除以 0.0250，得到 0.0980 mol dm-3。体积单位要从 cm3 换成 dm3，除以 1000 这一步漏掉，答案会差三个数量级。方程式系数不是 1 比 1 时要多一步，硫酸和氢氧化钠是 1 比 2，算完酸的物质的量要乘 2 才是碱的量。学生最常把 c = n / V 里的 V 用 cm3 代入，数字看起来合理但量纲不对，阅卷时只给过程分。卷面上单位要写在每一步后面，mol、dm-3 和 cm3 混着写会丢单位分。
Titration arithmetic runs in three moves: work out the amount in moles of the known solution, convert through the ratio in the equation, then divide by the volume to get the concentration. For 25.0 cm3 of sodium hydroxide neutralised by 24.50 cm3 of 0.100 mol dm-3 hydrochloric acid, the acid amounts to 0.100 multiplied by 24.50 over 1000, or 0.00245 mol, and the 1:1 ratio in HCl + NaOH -> NaCl + H2O makes the alkali 0.00245 mol in 0.0250 dm3, giving 0.0980 mol dm-3. Candidates frequently substitute a volume in cm3 into c = n / V, which produces a tidy but wrongly scaled answer that earns process marks only.
阅卷口径：三组对比的常见失分 / Where mark schemes take the marks
解释题的分数给在理由上，写"因为它是弱酸"只拿一分，写"弱酸只部分电离，所以同浓度下 H+ 浓度更低"才拿满。答题方向跟着题目的动词走，describe 写现象，比如气泡、蓝色溶液、石灰水变浑浊，explain 写原因，比如离子、电离程度、系数比。画图题要把起点、垂直段和终点趋势都画出来，pH 曲线的垂直段位置决定分数高低。计算题的过程分和答案分分开给，单位漏写会丢单位那一分。文字题里带上"在水中"这三个字通常不亏，酸碱的定义、电离和导电都靠它。考前把 3.1 到 3.14 的条目对着 spec 过一遍，每条写一句自己的话，两小时能过完一遍。
Marks go to the reasoning rather than the label, so "because it is a weak acid" earns one mark while "a weak acid only partially ionises, so the hydrogen ion concentration is lower" earns the full allocation. Command words set the shape of the answer: describe asks for observations such as bubbles, a blue solution or milky limewater, while explain asks for ions, degree of ionisation or mole ratios, and graph answers must place the vertical section correctly. Units carry their own mark in calculations, and the phrase "in aqueous solution" keeps definitions of acids, ionisation and conductivity on the mark scheme; two hours spent writing one sentence against each of entries 3.1 to 3.14 covers the whole topic once.
海外直订AQA GCSE Chemistry Student Book AQA GCSE化学学生手册¥588.0📱 去京东购买京东精选
需要一对一辅导？Need One-on-One Tutoring?
A-Level / GCSE / IB 全科辅导，复习计划与真题带练逐题拆解
16621398022 同微信
Visit aleveler.com
或截图后用「扫一扫 → 相册」选择本图