Answer to Question #29965 in Chemistry for Brianna Arnold

Question

A student used a volumetric pipet to measure the volume of the vinegar sample. The vinegar sample was titrated with NaOH and the acetic acid concentration was determined to be 4.20 %mass. For the second titration, the student used a graduated cylinder to measure the vinegar sample. The student calculated the concentration to be 4.30% mass. In which experiment should the student be more confident of the concentration of the acetic acid? Why?

Answer 1

In the first experiment the student was more confident of the concentration of the acetic acid. Because of surface tension, liquids dip inwards at the top. So in a graduated cylinder the dip has an effect on the measurement that the liquid is reaching. In a pipette, however, the tube which the liquid's in is much thinner, therefore the dip at the top is much less noticeable and has a considerably smaller difference. This, for obvious reason, makes it more accurate.