Required Practical 9 - Titration Curves

Describe a method to obtain a titration curve from HCl and NaOH.

1. Add 25cm³ HCl to a conical flask using a volumetric pipette and filler

2. Measure the initial pH of the acid

3. Add the NaOH to the burette

4. Add the NaOH in about 2cm³ increments, stirring and measuring the pH each time

5. Approaching the end point, add smaller volumes each time

6. Continue until alkali is in excess

Describe how to calibrate the pH meter before producing a titration curve.

Measure a known pH of buffer solution with the pH meter and note the pH reading

Repeat with other buffers

Plot a calibration curve of real pH against reading

How is the titration curve plotted for the experiment?

Use the calibration curve to covert measured pH values into real pH values and plot these

Explain how to find the equivalence point from a plotted titration curve.

Extrapolate the levelled sections of the graph and find the midpoint of the vertical line between them

How is Ka found from a titration curve?

pKa = pH at half equivalence

Why should the pH probe be rinsed with distilled water between readings?

To wash off any remaining solution to avoid effecting the readings

Why should the mixture be stirred before recording the pH?

To ensure the pH is equalised