Halochromy

Halochromy ("salt color") is the chemistry of changing the color of a substance depending on the charge state of its molecules.

Halochromes show color shifts when the state of charge changes (for example when salt is formed). This phenomenon in the chemistry of dyes can be observed in various acid-base indicators (for example phenolphthalein or litmus ). As a weak organic acid, phenolphthalein is uncharged and colorless in a weakly acidic to neutral environment. In alkaline solutions, the indicator molecule shows a red color due to its negative charge. Litmus changes its color from red (acidic) to blue (basic) depending on the pH value of an aqueous solution.

See also

• Bathochromic effect
• Hypsochrome effect

literature

• Entry on halochromy. In: Römpp Online . Georg Thieme Verlag, accessed on January 4, 2017.