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 …show more content…
for an indicator in an aqueous solution is:
HIn(aq) +H2O(i) H3O(aq) ++In(aq) -
Or
HIn(aq)H(aq) ++In(aq) -
Yellow Blue (Conjugate Base)
Where HIn= An indicator H += The resultant Conjugate base In -= The resultant Conjugate acid.
As known from the titration experiment previously, Thymol blue changes from yellow within its vial to a blue when in a Basic solution (NaOH) and changes back to a yellow color when subject to an acidic compound (Malic acid). This shows that that the higher the concentration of acidic H +There is in a solution with the indicator Thymol blue, the resulting color is yellow. Vice versa, the higher concentration of the basic OH - there is within the solution of thymol blue, the resulting color is blue. Additionally, as its starting color is yellow, thymol blue must be an indicator containing a weak acid.
Thus, using the experimental data from previously:
2NaOH(aq) + C4H6O5 (aq)2H2O(i) +Na2C4H4O5(aq)
The thymol blue indicator in the solution is shown to be blue when put into the NaOH solution.
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
acid contains very little H cations, thus more Thymol Blue is ionized in the OH supplied by the Sodium Hydroxide.
As malic acid was added into the solution, the Hydrogen (H +) ion concentration in the solution begins to increase as the amount of malic acid was added was rising. This reverses the equilibrium and while the concentration of H +rises, the equilibrium of the equation begins to travel towards the opposite side of the equation (to the right using above example). When this is happening, the thymol blue begins reverse ionizing and transforms color to become yellow as it shifts away from being the color of its state as a conjugate base. As more and more H +is added, this color change becomes more apparent, eventually being noticeable. The reason this happens is because of le chatelier's principle, as the forward equation is reversible into the backward equation. This means that when the equilibrium is first on one side and is either moved forward or reversed by adding something into (a base or acid in this case) that that would change it, the color of the indicator begins to ionize or reverse ionize based on the amount of excess H+or OH -ions that are added into the solution. This thought can be summed up as:
When the indicator is first put into a solution of only NaOH
HThy(aq)H(aq) ++Thy(aq) -
The overall equilibrium of the of the equation, shifts almost completely to the left. The majority of the Thymol blue is ionized within the NaOH solution, causing the color of the indicator to match its conjugate base, becoming blue. (H(aq) ++Thy(aq) -)
When malic acid is added to the solution of NaOH
HThy(aq)H(aq) ++Thy(aq) -
The overall equilibrium of the equation begins shifting to the right, causing more and more thymol blue ions reverse ionization, thus changing color back into its original state - Yellow. (HThy(aq))
The basic equilibrium equations …show more content…
for an indicator in an aqueous solution is:
HIn(aq) +H2O(i) H3O(aq) ++In(aq) -
Or
HIn(aq)H(aq) ++In(aq) -
Yellow Blue (Conjugate Base)
Where HIn= An indicator H += The resultant Conjugate base In -= The resultant Conjugate acid.
As known from the titration experiment previously, Thymol blue changes from yellow within its vial to a blue when in a Basic solution (NaOH) and changes back to a yellow color when subject to an acidic compound (Malic acid). This shows that that the higher the concentration of acidic H +There is in a solution with the indicator Thymol blue, the resulting color is yellow. Vice versa, the higher concentration of the basic OH - there is within the solution of thymol blue, the resulting color is blue. Additionally, as its starting color is yellow, thymol blue must be an indicator containing a weak acid.
Thus, using the experimental data from previously:
2NaOH(aq) + C4H6O5 (aq)2H2O(i) +Na2C4H4O5(aq)
The thymol blue indicator in the solution is shown to be blue when put into the NaOH solution.
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
acid contains very little H cations, thus more Thymol Blue is ionized in the OH supplied by the Sodium Hydroxide.
As malic acid was added into the solution, the Hydrogen (H +) ion concentration in the solution begins to increase as the amount of malic acid was added was rising. This reverses the equilibrium and while the concentration of H +rises, the equilibrium of the equation begins to travel towards the opposite side of the equation (to the right using above example). When this is happening, the thymol blue begins reverse ionizing and transforms color to become yellow as it shifts away from being the color of its state as a conjugate base. As more and more H +is added, this color change becomes more apparent, eventually being noticeable. The reason this happens is because of le chatelier's principle, as the forward equation is reversible into the backward equation. This means that when the equilibrium is first on one side and is either moved forward or reversed by adding something into (a base or acid in this case) that that would change it, the color of the indicator begins to ionize or reverse ionize based on the amount of excess H+or OH -ions that are added into the solution. This thought can be summed up as:
When the indicator is first put into a solution of only NaOH
HThy(aq)H(aq) ++Thy(aq) -
The overall equilibrium of the of the equation, shifts almost completely to the left. The majority of the Thymol blue is ionized within the NaOH solution, causing the color of the indicator to match its conjugate base, becoming blue. (H(aq) ++Thy(aq) -)
When malic acid is added to the solution of NaOH
HThy(aq)H(aq) ++Thy(aq) -
The overall equilibrium of the equation begins shifting to the right, causing more and more thymol blue ions reverse ionization, thus changing color back into its original state - Yellow. (HThy(aq))