Would the following procedural errors result in an incorrectly high or low calculated percent NaOCl in commercial bleach solution?
A student failed to allow the volumetric pipet to drain completely when transferring the diluted bleaching solution to the Erlenmeyer flask. I get incorrectly low.
A student blew the last drops of solution from the pipet into the volumetric flask when transferring commercial bleaching solution to the flask. I get no effect.
A student began a titration with an air bubble in the buret tip. The bubble came out of the tip after 5 mL of Na2S2O3 solution had been released. I get incorrectly high.
Are these correct because this kind of question confuses me. Thank you!
Yes, your answers are correct! Let me explain the reasoning behind each response:
1. The student failed to allow the volumetric pipet to drain completely: This would result in an incorrectly low calculated percent NaOCl in the bleach solution. When there are remaining drops of solution left in the pipet, it means that the total volume transferred to the Erlenmeyer flask is less than the intended volume. As a result, the concentration of the solution would be higher than what is actually measured, leading to an underestimated percentage of NaOCl.
2. The student blew the last drops of solution into the volumetric flask: This procedural error does not have any effect on the calculated percent NaOCl. Blowing the last drops into the flask does not introduce any significant variation in the measured volume or the concentration of the solution.
3. The student began a titration with an air bubble in the buret tip: This would result in an incorrectly high calculated percent NaOCl. The presence of the air bubble initially reduces the volume of Na2S2O3 solution being added during the titration. As the bubble eventually comes out after releasing 5 mL of Na2S2O3 solution, the subsequent volumes measured will be higher than the true volume, leading to an overestimated concentration of NaOCl and consequently a calculated percent NaOCl that is higher than the actual value.
In summary, an incorrectly low calculated percent NaOCl would result from not allowing the pipet to drain completely, an incorrectly high percent would result from starting a titration with an air bubble, and there would be no significant effect when blowing the last drops into the volumetric flask.