<P> Phenol red (also known as phenolsulfonphthalein or PSP) is a pH indicator frequently used in cell biology laboratories . </P> <P> Phenol red exists as a red crystal that is stable in air . Its solubility is 0.77 grams per liter (g / l) in water and 2.9 g / l in ethanol . It is a weak acid with pK = 8.00 at 20 ° C (68 ° F). </P> <P> A solution of phenol red is used as a pH indicator, often in cell culture . Its color exhibits a gradual transition from yellow (λ = 443 nm) to red (λ = 570 nm) over the pH range 6.8 to 8.2 . Above pH 8.2, phenol red turns a bright pink (fuchsia) color . </P> <Table> <Tr> <Td_colspan="3"> Phenol red (pH indicator) </Td> </Tr> <Tr> <Td> below pH 6.8 </Td> <Td> </Td> <Td> above pH 8.2 </Td> </Tr> <Tr> <Td> 6.8 </Td> <Td> ⇌ </Td> <Td> 8.2 </Td> </Tr> </Table>

What is the color of phenol red at an acid ph