This 30ml (one ounce) bottle of o-Cresolphthalein is 0.04% w/v in Ethanol. Commonly used as a acid-base indicator, 8.2 (colorless) - 9.8 (violet). Comes packed in convenient squeeze bottle for dispensing by the drop.
What is an acid-base indicator?
An acid-base indicator is a weak acid or a weak base. Indicators have a very useful property - they change color depending on the pH of the solution they are in. This color change is not at a fixed pH, but rather, it occurs gradually over a range of pH values. This range is termed the color change interval. Each pH indicator is defined by a useful pH range. For example o-Cresolphthalein changes from colorless at 8.2 to violet at 9.8. And Bromothymol Blue has a useful range from 6.0 (yellow) to 7.6 (blue).
How are liquid indicators used?
Liquid pH indicators are used to test other solutions. A few drops of the right indicator added to an unknown solution can tell you its pH value. Chemists use pH indicators in a common laboratory procedure called titration. Here, an unknown substance is measured by carefully adding a solution of known concentration until a neutral point is reached. The neutral point is indicated by the color change of a pH indicator mixed in with the unknown solution.