Metacresol purple

Metacresol purple is a pH indicator used in chemistry to visually determine the acidity or alkalinity of a solution. It is a member of the cresol red family of dyes, which are known for their color-changing properties in response to changes in pH.

Chemical properties[edit | edit source]

Metacresol purple is a triphenylmethane dye, which means it is composed of three phenyl groups attached to a central carbon atom. It is a weak acid, with a pKa of 1.7 in water. This means it can donate a proton to a solution, which is what causes the color change.

The color of metacresol purple changes depending on the pH of the solution it is in. In acidic solutions (pH less than 1.7), it is yellow. In neutral or slightly alkaline solutions (pH between 1.7 and 8.2), it is purple. In strongly alkaline solutions (pH greater than 8.2), it is yellow again.

Uses[edit | edit source]

The primary use of metacresol purple is as a pH indicator in chemistry. It is used in titration experiments, where the goal is to determine the concentration of an unknown acid or base. The color change of the indicator signals when the reaction is complete.

Metacresol purple can also be used in biology to measure the pH of cellular components. For example, it can be used to measure the pH of lysosomes, which are acidic compartments within cells.

Safety[edit | edit source]

Like all chemicals, metacresol purple should be handled with care. It can cause skin and eye irritation, and may be harmful if swallowed or inhaled. Always use appropriate personal protective equipment when handling metacresol purple.

See also[edit | edit source]

Metacresol purple Resources
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