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?
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.