method chem
Assessing Sulphur Dioxide in Wine by Titration
Procedure
1. Transfer 20.0 mL of wine using a pipette to each of three 250 mL conical flasks.
2. To each flask add about 12 mL of 1 M sodium hydroxide solution and allow the flasks to stand for 15 minutes. This releases the SO2 bound in complex compounds in the wine.
3. Fill a burette with standard iodine solution. Record the initial burette reading and the concentration of the solution.
4. To one flask, add about 10 mL of 2 M sulfuric acid and 1–2 mL of starch indicator solution. Immediately titrate the mixture with iodine solution. Record the burette reading the moment the mixture turns permanently blue (end point).
5. Repeat the above steps with each of the other two flasks.
pH Level
Procedure
1. Fill up the beakers with 20mL of wine sample.
2. Wash the pH tube with distilled water so that no particles left behind and give wrong results.
3. After washing the pH tube, put the pH tube in the wine sample beaker and wait till the pH machine comes up with the accurate answer.
4. Repeat step 1-3 for the other 2 samples.
Tithable Acidity
Procedure:
Using phenolphthalein indicator
1 Fill the burette with 0.1 M NaOH.
2 Add approximately 100 mL of distilled water to a 250 mL conical fl ask.
3 Add 3 or 4 drops of phenolphthalein indicator to the fl ask and mix well.
4 Add 0.1 M NaOH from the burette to the fl ask until the solution turns a pale pink colour that persists for at least 30 seconds. This usually takes only a few drops, and there is no need to record this volume.
5 Pipette 10.0 mL of the degassed wine or juice into the conical fl ask.
6 Record the initial burette reading.
7 Titrate the solution in the fl ask with NaOH until the pink colour again persists for at least
30 seconds.
8 Record the fi nal burette reading and calculate the difference between the initial and fi nal readings. This is called the titre value.
9 Repeat the titration until consistent titres are
Procedure
1. Transfer 20.0 mL of wine using a pipette to each of three 250 mL conical flasks.
2. To each flask add about 12 mL of 1 M sodium hydroxide solution and allow the flasks to stand for 15 minutes. This releases the SO2 bound in complex compounds in the wine.
3. Fill a burette with standard iodine solution. Record the initial burette reading and the concentration of the solution.
4. To one flask, add about 10 mL of 2 M sulfuric acid and 1–2 mL of starch indicator solution. Immediately titrate the mixture with iodine solution. Record the burette reading the moment the mixture turns permanently blue (end point).
5. Repeat the above steps with each of the other two flasks.
pH Level
Procedure
1. Fill up the beakers with 20mL of wine sample.
2. Wash the pH tube with distilled water so that no particles left behind and give wrong results.
3. After washing the pH tube, put the pH tube in the wine sample beaker and wait till the pH machine comes up with the accurate answer.
4. Repeat step 1-3 for the other 2 samples.
Tithable Acidity
Procedure:
Using phenolphthalein indicator
1 Fill the burette with 0.1 M NaOH.
2 Add approximately 100 mL of distilled water to a 250 mL conical fl ask.
3 Add 3 or 4 drops of phenolphthalein indicator to the fl ask and mix well.
4 Add 0.1 M NaOH from the burette to the fl ask until the solution turns a pale pink colour that persists for at least 30 seconds. This usually takes only a few drops, and there is no need to record this volume.
5 Pipette 10.0 mL of the degassed wine or juice into the conical fl ask.
6 Record the initial burette reading.
7 Titrate the solution in the fl ask with NaOH until the pink colour again persists for at least
30 seconds.
8 Record the fi nal burette reading and calculate the difference between the initial and fi nal readings. This is called the titre value.
9 Repeat the titration until consistent titres are