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.)
thank you!
See my latest response at the original post.
To answer these questions, let's analyze each scenario based on the provided background information:
1. After rinsing the buret with distilled water and filling it with the standard NaOH solution, the acid is titrated to its equivalence point.
Explanation: In this scenario, the rinsing of the buret and filling it with NaOH solution should not affect the calculated molarity of the acid. The purpose of rinsing the buret is to ensure that any impurities or residues are removed, which could potentially affect the accuracy of the titration. Filling the buret with NaOH solution is the standard solution used for the titration, so it will not alter the calculated molarity of the acid.
Conclusion: Not affected.
2. Phenolphthalein changes color around pH 9 to signal the equivalence point; an indicator that changes color around pH 5 is used instead.
Explanation: In this scenario, changing the indicator from phenolphthalein (pH 9) to an alternative indicator that changes color around pH 5 can potentially affect the calculated molarity of the acid. The choice of indicator determines the endpoint of the titration. If a different indicator with a different pH range is used, it may lead to an incorrect endpoint determination, resulting in an inaccurate calculated molarity of the acid.
Conclusion: Potentially affected if the indicator used has a different pH range.
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).
Explanation: In this scenario, the presence of an air bubble in the buret can affect the measured volume of the NaOH solution and, consequently, affect the calculated molarity of the acid. When an air bubble is present, it occupies an actual volume in the buret, leading to the incorrect perception of the amount of liquid dispensed. This error can result in an overestimation or underestimation of the volume of NaOH solution used, affecting the calculated molarity of the acid.
Conclusion: Potentially affected if the air bubble affects the measured volume of the NaOH solution.
In summary, the calculated molarity of the acid would potentially be affected by the choice of indicator (scenario 2) and the presence of an air bubble in the buret (scenario 3). However, rinsing the buret with distilled water and filling it with NaOH solution (scenario 1) should not affect the calculated molarity.