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

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

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.

Indicator Transition pH range Phenol red Yellow 6.4 – 8.0 Red Bromothymol blue Yellow 6.0 – 7.6 Blue Phenolphthalein Colorless 8.3 – 10.0 fuchsia Litmus Red 5.0 – 8.0 Blue

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 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 < 8.3 4.6 – 8.3 3.8 – 5.4 5.0 – 5.4 pH 5.0 – 5.4