Once the liquid level rises above the mark on the volumetric flask, the exact volume of solution is no longer known, so the concentration of the solution cannot be determined with the volumetric flask. Do not remove excess liquid with a medicine dropper; a portion of the solute will probably be removed as well. Adding more solute will not fix the error, since the volume of liquid is still unknown. Do not use the solution as it was prepared. Instead, dispose of the solution in the appropriate waste container and prepare a new solution with the proper volume.
What is wrong with the procedure shown in Self Check video 2?
Answer
In the video, the student first added distilled water to the volumetric flask and then added the dissolved solute. He should
have added the dissolved solute first and then filled the flask to the mark with distilled water. The incorrect order of the procedure increases the chance that the solution level will rise above the mark on the flask, since the student doesn't know exactly how much distilled water to add initially.
How could the student have avoided the problem in Self Check video 3?
Answer
The student is trying to dissolve a solid in the volumetric flask. He should have dissolved the solid in a beaker first and then added the solution to the volumetric flask. Had he used a beaker, he could have heated the solution on a hot plate, which would have helped dissolve the solid more quickly.
What should you do to correct the error in Self Check video 1?