Question

Question #c47f5

Answer 1

The appropriate concentration of NaOH is 0.1 mol/L.

A titration burette contains 50 mL of titrant. We should design our experiment to as much of this as possible. This will reduce the percent uncertainty in the measurement.

Aspirin has the formula C₉H₈O₄ and a molar mass of 180.2 g/mol.

Let's use the formula HA for aspirin. Then the equation for the reaction is

HA + NaOH → NaA + H₂O

The amount of NaOH required is

0.250 g HA × `"1 mol HA"/"180.2 g HA" × "1 mol NaOH"/"1 mol HA"` = 0.001 39 mol NaOH

If we use 0.01 mol/L NaOH, the volume required is

0.001 39 mol NaOH × `"1000 mL NaOH"/"0.01 mol NaOH"` = 139 mL NaOH.

This is too big a volume. We would have to refill the buret to complete the titration.

If we use 0.1 mol/L NaOH, the volume required is

0.001 39 mol NaOH × `"1000 mL NaOH"/"0.1 mol NaOH"` = 13.9 mL NaOH.

We should use 0.1 mol/L NaOH, because that uses a convenient volume of titrant.

Here is a video that involves a titration of aspirin with NaOH.