The indicator Methyl Yellow changes from red to yellow over the pH range of 2.9-4.0. A second indicator, Bromcresol Purple., changes from yellow tored over the pH range of 5.4 - 6.8. You conduct an experiment in which a sample of HCl is titrated with NaOh, and HCl is the titrant. At the end of the experiment, the solution in the beaker is red. Which indicator was used?

Question

The indicator Methyl Yellow  changes from red to yellow over the pH range of 2.9-4.0. A second indicator, Bromcresol Purple., changes from yellow tored over the pH range of 5.4 - 6.8. You conduct an experiment in which a sample of HCl is titrated with NaOh, and HCl is the titrant. At the end of the experiment, the solution in the beaker is red. Which indicator was used?

Is it Bromscresol Purple?

DrBob222 · Answer

A couple of points. If HCl is the titrant, your statement should be "a sample of NaOH is titrated with HCl" and if you do it that way you do not need the statement that HCl is the titrant. Second point is that the problem doesn't make it clear how much HCl was added (actually it could have been zero HCl "at the end of the experiment."
I assume some HCl was added; therefore, the solution was red at the beginning from the BCP and the only way it can be red again is on the acid side of MY. Thus, there are two answers; it could have had no HCl added and the indicator is BCP or it could have all of the NaOH titrated (or most of it) and MY was used.
Red|....MY....|YxxxxY|.....BCP.....|R