1. How simple indicators work.
Indicators as weak acids (Litmus):
Adding hydroxide ions (OH-):

2. How simple indicators work.
Indicators as weak acids (Litmus):
Adding hydrogen ions (H+):

3. How simple indicators work.
Indicators as weak acids (Phenolphthalein):
Adding hydrogen ions (H+):
Adding extra H+ the equilibrium will shift to
the left ---- Colorless.
Adding hydroxide ions (OH-):
The OH- react & remove the H+,the
equilibrium will shift to the right ---- Pink.

4. Indicator Transition
pH range
Phenol red Yellow – Red
Bromothymol blue Yellow – Blue
Phenolphthalein Colorless – fuchsia
Litmus Red – Blue

5. Estimate the pH of the following solution:
- Phenolphthalein – turns to colorless
- Bromophenol blue – turns to purple
- Bromocresol green – stay green
- Congo red—stay red. pH
< 8.3
> 4.6
3.8 – 5.4
> 5.0
< 8.3
4.6 – 8.3
3.8 – 5.4
5.0 – 5.4
pH 5.0 – 5.4