Question

How do you calculate the endpoint of a titration?

Answer 1

Hint: To answer this question we should know what titration and endpoint are. Titration is a method used for the determination of the concentration of an unknown substance. During a titration, the point at which the reaction completes is known as the endpoint. During titration a chemical reaction takes place. We take one substance whose concentration is known and the second whose concentration is unknown. We determine the concentration of the unknown.

Complete step by step answer:
The substance whose concertation we determine is known as titer. For this, we use a substance whose concentration is known. This substance is known as titrant or titrator. The titrant is a solution whose concentration and volume are known. The endpoint is determined by some physical change, generally colour change. We will understand the titration and endpoint by taking an acid-base neutralization titration example.
${\text{HCl}}\,{\text{ + }}\,{\text{NaOH}}\, \to {\text{NaCl}}\,{\text{ + }}\,{{\text{H}}_{\text{2}}}{\text{O}}$

We take the solution of base sodium hydroxide whose concentration and volume are known. Then we take a fixed amount of acid in a conical flask. We add the base dropwise in the conical flask containing the acid. We also add an indicator. As we add base in acid, a chemical reaction takes place. So, the salt sodium chloride and water forms. The final drop of the base at which the indicator shows a colour or colour change represents the endpoint or completion of the reaction. We recode that volume of base.

Then we use the following formula to determine the concentration of acid.
${{\text{M}}_{{\text{HCl}}}}{\text{V}}{\,_{{\text{HCl}}}}\, = \,{{\text{M}}_{{\text{NaOH}}}}{{\text{V}}_{{\text{NaOH}}}}$
We know the volume of acid (we took initially) and base (recorded at endpoint) and we know the concentration of base so we can calculate the concentration of acid.

Therefore, the endpoint of a titration is determined by a change in colour of the acid-base titration.

Note: Titration is a volumetric analysis. The compound which shows different colour in acidic and basic medium or colour in one type of medium is known as an indicator. The indicator generally used for acid-base neutralization titration is phenolphthalein. Phenolphthalein shows pink colour in basic medium and remains colourless in acidic medium.