Haha, thanks.
Given a class prac, we need to find the titratable acidity content in wine, as expressed if all is tartaric acid, which is a diprotic acid with molar mass 150g mol
-1. I'm having trouble understanding what this means and would really appreciate an explanation.
Also, I'm unsure about the purpose of step 4 in our experiment of determining acidity in wine:
1. Fill the burette with NaOH.
2. Add approx 100mL of deionised water to a 250mL conical flask.
3. Add 3 or 4 drops of phenolphthalein indicator to the flask and mix well.
4. Add 0.1M NaOH from the burette to the flask until the solution turns a pale pink colour that persists for at least 30 seconds. This takes only a few drops and there is no need to record this volume.5. Pipette 10.0mL of wine into conical flask and record initial burette reading.
6. Titrate the solution in the conical flask with NaOH until the pink colour again persists for at least 30 seconds.
7. Record final burette reading and repeat steps to obtain concordant titres.
Does this mean that the pink colour fades when we do step 5? Otherwise, how are we expected to see the pink colour change as mentioned in step 6? Had we omitted this step, that is pipetted the wine with the deionised water and phenolphthalein (without a drop of NaOH), would it have made any difference?
Can someone please also explain the need for adding the 100mL of water? I understand that it does not change the total amount of acid in the sample, so still unsure why step 2 is necessary.
All of your help is appreciated! Thank you