Purpose: To use titration to find the pH and unknown concentration of an acid.
Procedure:
- Weigh the candy and record one candy’s mass. Weight out 5.0-10.0g and record the mass.
2. Grind the candy into a powder.
3. Dissolve the powder into 50.0 mL of water, filter if needed.
4. Add 10.0 mL of the sample into an erlenmeyer flask, add a few drops of phenolphthalein.
5. Titrate 0.10 NaOH into the sample until a colour change occurs. Record the volume reading on the burette in the data table.
6. Repeat steps 4 and 5 for two more trials.
7. Use the data known to calculate the unknown concentration of the acid and pH.
Materials:
- Sweet Tarts
- 50 mL of water
- Phenolphthalein (pH 7)
- Erlenmeyer flask
- Burette, clamp, and stand
- Grinder
Data:
Mass of candies: 8.08 g (7 Sweet Tarts)
Volume recorded:
Trial 1: 7.0 mL
Trial 2: 7.5 mL
Trial 3: 8.7 mL
Calculations:
Conclusion:
This experiment was completed to determine the pH of 10.0ml of malic acid using titration. The final pH that was measured is 1.11 comparing to the actual pH of sweetarts (2.2). The error that may have occurred is that we measured the NaOH to the nearest mL; if we had measured to the nearest 1/10 of a mL the results may have been more accurate. If we had added the base into the acid at a slower pace, we may have been able to better narrow down the pH where the colour change occurred. Therefore our results for pH would have been more accurate.