pH Indicators:
An indicator is simply a weak organic acid or base in which the dissociated and undissociated forms are different colors. The color change is caused by a change in the ratio of dissociated to undissociated forms in response to pH. The typical human eye can distinguish a change in this ratio by about a factor of 10-100, so many indicators appear to change color over about 1-2 pH units (1-2 orders of magnitude change in the hydronium ion concentration). For a simple indicator, the concentrations of these two forms are equal when the pH is equal to the indicator pKa or pKb.
The colors and pH ranges shown here are approximate only. The actual indicator color may change with solvent, temperature, the presence of ions and indicator concentration. Variations in the ability to perceive color may also vary considerably from individual to individual.
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An indicator is simply a weak organic acid or base in which the dissociated and undissociated forms are different colors. The color change is caused by a change in the ratio of dissociated to undissociated forms in response to pH. The typical human eye can distinguish a change in this ratio by about a factor of 10-100, so many indicators appear to change color over about 1-2 pH units (1-2 orders of magnitude change in the hydronium ion concentration). For a simple indicator, the concentrations of these two forms are equal when the pH is equal to the indicator pKa or pKb.
The colors and pH ranges shown here are approximate only. The actual indicator color may change with solvent, temperature, the presence of ions and indicator concentration. Variations in the ability to perceive color may also vary considerably from individual to individual.
