So i had trouble finding the answers to these questions on a lab:
Background: If we were using a burret/flask instead of a pipette and well plates. Before you started, the buret must be rinsed with 1 ml of distilled water and then 1 ml of NaOH solution. The flask would also be rinsed with 1 ml of distilled water and 1 ml of vinegar.
Questions: Based on the background info. above, predict how the calculated molarity of the acid would be affected (too high, too low, or not affected) by the following lab procedures. (then explain your answer)
1.) After rinsing the buret with distilled water, the buret is filled with the standard NaOH solution; the acid is titrated to its equivalence point.
2.) Phenolpthalein changes color around pH of 9 to signal the equivalence point; an indicator that changes color around pH of 5 is used instead.
3.) An air bubble of some size was present in the buret at the end of the experiment (it was pushed in after the lab started.)
My thoughts:
Wouldn't number 2 create a higher molarity since the lower pH would make it acidic?
and number 3 wouldn't it stay relatively unchanged since the bubble was formed after the experiment?
Thanks for your help :]
See my latest response at your original post.
To answer these questions, let's analyze each scenario based on the background information provided:
1.) After rinsing the buret with distilled water, the buret is filled with the standard NaOH solution; the acid is titrated to its equivalence point.
In this scenario, the calculated molarity of the acid would not be affected. This is because the buret is initially rinsed with distilled water, which does not react with the acid. Additionally, filling the buret with NaOH solution does not affect the molarity of the acid being titrated. The molarity of the acid can only be affected by the concentration, volume, and reaction stoichiometry during the titration process.
2.) Phenolphthalein changes color around pH of 9 to signal the equivalence point; an indicator that changes color around pH of 5 is used instead.
Using an indicator that changes color around pH 5 instead of pH 9 could potentially affect the calculated molarity of the acid. This is because the indicator may change color before, or after, the true equivalence point. If the indicator changes color before the equivalence point, the calculated molarity of the acid would be too high. If the indicator changes color after the equivalence point, the calculated molarity of the acid would be too low. Therefore, the exact impact on the calculated molarity would depend on when the indicator actually changes color relative to the true equivalence point.
3.) An air bubble of some size was present in the buret at the end of the experiment (it was pushed in after the lab started).
The presence of an air bubble in the buret at the end of the experiment would not affect the calculated molarity of the acid. This is because the air bubble does not participate in the chemical reaction between the acid and the base being titrated. As long as the volume of the air bubble is known and accounted for during the calculations, it will not have an impact on the calculated molarity.
So, in summary:
1.) The calculated molarity of the acid would not be affected.
2.) It could be affected, depending on when the indicator changes color relative to the true equivalence point.
3.) The calculated molarity of the acid would not be affected as long as the volume of the air bubble is accounted for during calculations.
I hope this explanation helps! Let me know if you have any further questions.