5. Describe a chemical indicator. What is it? What is it used for? How does it work?
Biology · Middle School · Sun Jan 24 2021
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Chemical indicator, any substance that gives a visible sign, usually by a colour change, of the presence or absence of a threshold concentration of a chemical species, such as an acid or an alkali in a solution.
An example is the substance called methyl yellow, which imparts a yellow colour to an alkaline solution.
Work : If acid is slowly added, the solution remains yellow until all the alkali has been neutralized, whereupon the colour suddenly changes to red.
Use : Like most indicators, methyl yellow is visible even if its concentration is as low as a few parts per million parts of solution. Used at such low concentrations, indicators do not have any influence on the conditions for which they are recommended. The common application of indicators is the detection of end points of titrations.