Procedures:

 

• Accurately weigh 10.0 ± 0.1 g sample of the yoghurt into two white porcelain basin. Add 10 ml of water and stir thoroughly with magnetic stirrer to ensure complete mixing.

 

• Add 1.0 ml of the phenolphthalein indicator into each of the porcelain basin and mix thoroughly by stirring with a magnetic stirrer.

 

• Rapidly, and with constant stirring, add 0.1 M NaOH from a burette until a faint pink colour remains for at least 10 s. Note the volume of alkalis used and repeat the titration. The time for the titration should not exceed 30 s for each sample and the results should agree within 0.05 ml.

 

ATTENTION:

 

• Ensure that the pink colour remains for at least 10 s.

 

• Ensure thorough mixing of the yoghurt and NaOH during titration. 

 

• Ensure drop by drop addition of NaOH to prevent overshoot of titration.

 

• Ensure that the burette is not slanted during titration to ensure proper reading of the volume of the NaOH used.

 

• Ensure sufficient time is allocated between each addition of NaOH as the yoghurt can be quite viscous.