定义Definition
通用指示剂（广泛 pH 指示剂）是几种酸碱指示剂的混合物，在 pH 1 到 14 的范围内呈现一系列连续变化的颜色，可用来粗略估计溶液的 pH。常见颜色：强酸性为红色，弱酸性为橙至黄色，中性为绿色，弱碱性为蓝色，强碱性为紫色。
Universal indicator is a mixture of several acid–base indicators that gives a gradual series of colours from pH 1 to 14, used to estimate pH roughly. Typical colours: red for strongly acidic, orange to yellow for weakly acidic, green for neutral, blue for weakly alkaline and purple for strongly alkaline.
使用与局限Use and limitations
把溶液滴在 pH 试纸上或向溶液中加几滴指示剂，与比色卡对照读数，精度约为 1 个 pH 单位。它颜色变化是渐变的，没有明显的突变点，所以不适用于滴定；需要准确数值时应用 pH 计。
Spot the solution onto pH paper or add a few drops of indicator and compare with the colour chart; it is accurate to about one pH unit. Because the colour changes gradually with no sharp end point, it is unsuitable for titrations; a pH meter is used when an accurate value is needed.