<Tr> <Td> CAS Number </Td> <Td> <Ul> <Li> 115 - 39 - 9 </Li> </Ul> </Td> </Tr> <Ul> <Li> 115 - 39 - 9 </Li> </Ul> <Li> 115 - 39 - 9 </Li> <Tr> <Td> 3D model (JSmol) </Td> <Td> <Ul> <Li> Interactive image </Li> </Ul> </Td> </Tr>

The purpose of the bromophenol blue indicator in the titration is