Ph Indicator Lab Report

pH indicators, in chemistry, are usually a weak acid or base that are naturally occurring in various plants and flowers and can act as dyes. Some examples of indicators are Litmus (Comes from a plant species called a lichen), Phenolphthalein, Thymol blue, Bromocresol green and Universal indicator. All these indicators have a certain turning point in color once a certain concentration equilibrium of Hydrogen cations in reached (H +) or a certain concentration equilibrium of H3O+(Also OH - using Arrhenius theory) is reached. These indicators acids and conjugate bases have different colors, that change dependent on where the equilibrium is found between an equations acid or conjugate base. This equilibrium follows le chatelier's principle.

The basic equilibrium equations
However when the malic acid was added from the burette into the conical flask containing the solution, the color shown by the indicator changed from blue into yellow. Thus this means that when Thymol Blue is un-ionized, it will have a Yellow color and when it is ionized (broken down) in a base, it turns into a blue color. This is an example of Le Chatelier's Principle.

As Le Chatelier's principle states, adding more of a substance to one side of the equation, shifts the equilibrium to the opposite side. This same effect applies to the indicators in a solution. In the case of NaOH and Malic acid titration; before the malic acid was added to the solution, all that remained was a solution of NaOH and Thymol blue, at this stage the thymol blue was Mostly ionized within NaOH (The Hydroxide ion reacts with the Thymol Blue), thus giving off a blue color, as there is an abundance of Hydroxide anions and not enough Hydrogen cations in the solution.

HThy(aq)H(aq) ++Thy(aq) -
I_______I - Equilibrium point is closer to this side, as the overall solution without malic