A student began adding titrant to the acid solution, but stopped when she suddenly realized that she forgot to add the 3 drops of phenolphthalein. When she did, the solution immediately turned dark red!
What can the student do to correct this error and salvage this trial, so she doesn't have to redo it? What corrections or modifications will have to be made to her recorded data?
The student can add acid back to the solution. The acid can be either a standardized solution (the student will need the volume and the molarity of the standardized acid added) or the student can add a known mass of a solid acid. So,e care must be used in what acid to use in either case.
To correct the error and salvage the trial, the student can follow these steps:
1. Carefully transfer the dark red solution into a clean flask.
2. Add a few drops of a weak acid (e.g., dilute hydrochloric acid or acetic acid) to the flask. This will help neutralize the excess base present in the solution.
3. Re-add the phenolphthalein indicator to the flask.
4. Slowly add the titrant back into the solution until the color changes as desired (e.g., pale pink).
5. Record the volume of titrant added during this correction process.
Now, let's discuss the corrections or modifications that will need to be made to the recorded data:
1. The volume of titrant added during the correction process should be subtracted from the initial volume recorded.
2. Since the phenolphthalein was not added initially, the endpoint of the titration may have been reached without the student realizing it. Therefore, the recorded volume of titrant before the correction should be adjusted to account for this potential discrepancy.
3. If the color change occurred before adding the corrective acid, the student should note that the trial was not valid and consider it as a failed trial.
Remember, it is important to maintain accurate and precise records of experimental data, including any modifications or corrections made during the process.