End Point In Acid-Base Titration

845 Words4 Pages
Discussion: 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 reacted and can be determine via the…show more content…
For this titration, any indicator can be used because the graph is very steep which because no difference in the volume of alkali added to whichever indicator. For experiment B, weak acid and strong base (CH3COOH-NaOH), the titrations have been repeated with two different indicators which are methyl orange and phenolphthalein. It is shown that phenolphthalein is a better indicator because the pH range of the titration lies between the pH ranges of the phenolphthalein. Methyl orange is not a suitable indicator because it changes colour early in the experiment. For experiment C, between an unknown weak acid and a strong base (NaOH), phenolphthalein is used as an indicator. 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

More about End Point In Acid-Base Titration

Open Document