Question

A student titrates a solution of known volume and concentration of H2C204 (oxalic acid) to determine the concentration of NaOH. The indicator used is phenolphthalein. Draw and label the apparatus used for the titration. Identify both the glassware and their contents. Describe what colour the solution would be in the flask at the beginning of the titration and at the end of the titration.

Answer 1

During titration to determine the concentration of NaOH using oxalic acid (
`H_2C_2O_4`) and phenolphthalein as an indicator, the color of the solution in the Erlenmeyer flask would change from colorless to brilliant pink when neutrality is reached.

In a titration, the student uses a burette filled with a known concentration of NaOH solution and an Erlenmeyer flask containing a solution of
`H_2C_2O_4` (oxalic acid) along with a few drops of the indicator phenolphthalein. The burette allows precise and controlled addition of the NaOH solution to the oxalic acid solution in the flask.

At the beginning of the titration, the solution in the flask appears colorless because phenolphthalein is colorless in acidic solutions. As the base (NaOH) is gradually added to the acid solution, the phenolphthalein undergoes a color change. In the presence of excess base, phenolphthalein turns a brilliant pink color, signaling the endpoint of the titration.

The color change indicates that the acid has been neutralized by the base, and the solution has shifted from acidic to neutral or slightly basic. The volume of NaOH solution required to achieve this color change can be used to calculate the concentration of NaOH, providing valuable information about the concentration of the acid in the initial solution. Phenolphthalein serves as a visual indicator, making it easier for the student to identify the endpoint of the titration accurately.