Acid Base Lab Report

05/26/10
Elizabeth Angermyer Period: 4

Strong Acid and Weak Base Lab

PURPOSE: To find the molarity of an unknown acidic acid.

MATERIALS: 1. 250 mL beaker 2. 10 mL graduated cylinder 3. 50 mL beaker 4. Funnel 5. 125 mL Erlenmeyer flask 6. 50 mL buret 7. Ring stand 8. Strong acid 9. Weak base 10. Phenolphthalein 11. De-ionized water.

PROCEDURES: 1. Fill the buret with a weak base and place it in the ring stand. 2. Fill the 50 mL beaker with 30 mL of a strong acid. 3. Fill the 250 mL beaker with 50 mL of de-ionized water. 4. Pour around 9.5 mL of the strong acid into the graduated cylinder. 5. Pour the acid into the Erlenmeyer flask. 6. Pour around 10 mL of de-ionized water into the graduated cylinder. 7. Pour the water in the flask with the acid. 8. Put a couple drops of phenolphthalein into the flask and stir it to evenly distribute among the water and acid. 9. Place the flask under the buret. 10. Record the starting volume of the base in the buret. 11. Pour a little base into the flask. Mix it after each time. 12. Keep doing this until the mixture in the flask turns a pale pink color. 13. Record the ending volume of the base in the buret. Use the 2 volumes to figure out how much bas was used. 14. Use the data found to determine the molarity of the acid.

DATA: (Trial 1) * Amount of acid: 9.5 mL * Amount of de-ionized water: 10 mL * Starting volume of base: 0.3 mL * Ending volume of base: 34.4 mL
CALCULATIONS:

DISCUSSION & CONCLUSION: The molarity for the base wasn’t consistent for all 3 of my trials. For my 1st trial I got the molarity to be 0.2751. For my 2nd trial I got the molarity of 0.116, and for my 3rd trial I got the molarity to be 0.281. This could have happened for many reasons. In the 1st trial I used 9.5 mL of acid. From the amount of base used, I concluded that the acid was extremely strong. Because of the amount of base used, we decided to cut down on the amount of acid so we wouldn’t run out of base. We used 7.0 mL of acid hoping to use less base, however, the opposite occurred. For some reason we used over 25 mL more for this trial than we had in the 1st, even though we used less acid in the 2nd trial. I am still not sure exactly why that happened but maybe, it could be because we didn’t put enough phenolphthalein. We had to add some in the middle of the trial because we weren’t seeing any pink when the base hit the acid. We may have added too much because in the matter of a couple drops, it went from colorless to a bright fuchsia color. It took us the longest for this trial to get the solution to turn pink. For our 3rd trial we decreased the amount of acid even more, going from 7.0 mL to 5.0 mL. This time we didn’t use as much base as we did in the 1st and 2nd trials. It also took a lot less time to get to the pale pink color. I am not entirely sure why this happened because we used the same acid and base for all 3 trials. Maybe I measured the acid incorrectly when I was pouring it into the flask. Or, maybe I didn’t put enough of or put too much phenolphthalein. If I did this lab again I would double check my measurements, put the correct amount of phenolphthalein and make sure that I stirred the flask after each time I put the base into it.