Equivalence Point In An Acid-Base Titration

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End point in this acid-base titration experiment refers to the point where the chemical reaction has reached its conclusion and no additional titrant should be added. The end point of this experiment can be obtained when the indicator used changes colour. For example colourless to light pink when phenolphthalein is used and red to orange and subsequently yellow when methyl orange is used.
Equivalence point, also known as stoichiometric point in an acid-base titration refers to the point where the reacting acid and base is in equal proportions. In the graph plotted, pH against volume of NaOH, the graph becomes nearly vertical at the equivalence point. The equivalence point also indicates that all the initial reactants have been
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The pKa of this unknown weak acid is 4.0 and the Ka is 1.0 x 10-4 mol dm-3 while the molecular weight is 166.67 g mol-1. It is closely related to the ascorbic acid with a pKa of 4.10 and a Ka of 7.9 x 10-5 with a molecular weight of 176.12 g mol-1. Therefore it can be concluded that the unknown acid is ascorbic acid.
Titration technique is best suited for this experiment because the end point and equivalence point can be distinguished by the physical changes which are the colour change of the mixture. We are also able to better control and determine the volume of NaOH in the burette needed to neutralise HCI, CH3COOH and the unknown acid. This is because the amount of NaOH droplet can be altered when a burette is used thus, the NaOH solution can be dripped per drop at the time nearing the end point of the experiment as the colour changes rather quickly from light pink to pink.
In conclusion, titration is an effective technique to determine the equivalence point, pH range, pKa, Ka and molecular mass of the unknown acid of the acid-base reaction. This technique is dependent on the colour change of the indicator which makes it easier to determine the end point of the experiment. Postlab Exercises:
1. Please refer to results and
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