Indicator color charts are essential tools for accurately measuring the acidity or alkalinity of a substance. They rely on chemical compounds that shift hue in response to hydrogen ion concentration, allowing you to gauge pH quickly and reliably. This guide explains the science behind common indicators—litmus, Hydrion, and universal—and walks you through a clear, step‑by‑step method for interpreting results.
Litmus paper is the classic pH indicator. Red litmus turns blue when it comes into contact with a base, while blue litmus turns red in the presence of an acid. Simply dip the paper into the liquid you’re testing and observe the color change. This test tells you whether the solution is above or below neutral (pH 7).
Hydrion paper offers a more precise pH readout. Small‑range strips (e.g., pH 3–7) are ideal for detailed measurements, often displaying values to one decimal place (3.5, 4.2, etc.). Full‑range strips (pH 0–14) cover the entire spectrum but typically display whole‑number values. After applying the sample, match the resulting color to the chart provided on the package to determine the exact pH.
Universal indicators combine several dyes into a single reagent, producing a rainbow of colors across the entire pH spectrum. They are available in paper form and as liquid solutions. Apply the test substance to the paper or add it to the liquid, then compare the resulting hue to the color key. Generally, red indicates acidity, green signals neutrality, and purple denotes alkalinity.
Follow these steps to achieve accurate, repeatable pH measurements in the lab, classroom, or field.
