上一片认识了酸和碱：酸有酸味、能让石蕊变红；碱滑滑的、能让石蕊变蓝。可是"有点酸"到底有多酸？这次 ⚗️ 小烧瓶掏出一把 0 到 14 的标尺——pH 试纸和紫甘蓝汁，都来当它的刻度。Last leaf we met acids and bases: acids taste sour and turn litmus red; bases feel slippery and turn it blue. But how sour is “a bit sour”? This time ⚗️ the little flask pulls out a 0-to-14 ruler — pH paper and purple cabbage juice serve as its markings.
第 1 步：给酸碱度装一把尺子Step 1: A ruler for acidity
怎么把"酸一点、碱一点"说准确？先给它安上刻度。How do we say exactly how acidic something is? Give it a scale.
小烧瓶把尺子从 0 画到 14：pH 小于 7 是酸性，等于 7 是中性（纯水），大于 7 是碱性。柠檬大约 2，纯水正好 7，肥皂大约 9。记住这把尺子的脾气：每差 1，H⁺ 浓度就差 10 倍——pH 从 7 掉到 4，酸度整整强 1000 倍。The little flask draws the ruler from 0 to 14: below 7 is acidic, 7 is neutral (pure water), above 7 is basic. A lemon sits near 2, pure water exactly 7, soap near 9. Remember the ruler's temper: each step of 1 changes the H⁺ concentration 10 times — pH dropping from 7 to 4 means 1000 times more acidic.
尺子有了，可读数用什么？小烧瓶说：不用买试纸，菜篮子里就有。We have the ruler — what do we read it with? No need to buy paper, says the flask: the vegetable basket has one.
第 2 步：厨房里的"颜色温度计"Step 2: A color thermometer from the kitchen
紫甘蓝汁是天然指示剂：滴进柠檬汁变红，滴进清水保持紫色，滴进肥皂水变蓝绿。常见物质的 pH 顺手记一记：胃酸约 1.5、柠檬 2、牛奶 6.5、纯水 7、肥皂 9、漂白剂 13。要当心：强酸强碱会灼伤皮肤，只许看标签、做实验，不许随便尝。Purple cabbage juice is a natural indicator: into lemon juice it turns red, into plain water it stays purple, into soap water it turns blue-green. Useful pH values to remember: stomach acid ≈ 1.5, lemon 2, milk 6.5, pure water 7, soap 9, bleach 13. Careful: strong acids and bases burn skin — read labels and do experiments, never taste at random.
这把尺子只在实验室有用吗？花园说：我天天用它。Does this ruler only matter in the lab? The garden says: I use it every day.
第 3 步：土壤的 pH，花朵的颜色Step 3: Soil pH, the color of flowers
绣球花是天然的"pH 指示花"：酸性土里开蓝花，碱性土里开粉花。大多数作物喜欢 6~7 的微酸土壤；土太酸，农民就撒熟石灰把它"拉"回中间。熟石灰凭什么能拉回来？靠的就是下一片的主角——酸碱中和。Hydrangeas are natural pH flowers: blue in acidic soil, pink in basic soil. Most crops like slightly acidic soil around 6–7; when soil gets too sour, farmers spread slaked lime to pull it back toward the middle. What lets lime do that? The star of the next leaf — acid-base neutralization.
🎮 你来当调色师（30 秒）🎮 Your turn: color mixer (30 seconds)
道理讲完了。先拖 pH 滑块，看紫甘蓝汁的颜色一路过渡；再接 4 张物质卡，把它们放进正确的酸碱段。Theory done. First drag the pH slider and watch the cabbage juice shift color; then take 4 substance cards and place each in the right band.
一句话记住它：pH 是酸碱度的尺子：小于 7 酸、等于 7 中、大于 7 碱；每差 1，H⁺ 浓度差 10 倍。Remember it in one line: pH is the ruler of acidity — below 7 acid, 7 neutral, above 7 basic; each step of 1 means a 10-fold change in H⁺.
pH < 7 酸性，= 7 中性（纯水），> 7 碱性pH < 7 acidic, = 7 neutral (pure water), > 7 basic紫甘蓝汁是厨房指示剂：酸红、中紫、碱绿Purple cabbage juice: a kitchen indicator — red in acid, purple neutral, green in base常见谱：胃酸 1.5、柠檬 2、牛奶 6.5、肥皂 9、漂白剂 13Common chart: stomach acid 1.5, lemon 2, milk 6.5, soap 9, bleach 13
内容参考 OpenStax 等公开教材，多来源核对 · AI 生成、人工审核 · 发现错误欢迎指正，帮这片叶子长得更好。Based on OpenStax and other open textbooks, cross-checked across sources · AI-generated, human-reviewed · Spotted a mistake? Tell us — help this leaf grow.
Back to tree
