Repeat this titration with your other sample and calculate the NaOH concentration. Do not proceed until your results have been checked and approved by your teaching instructor. During titration the solution being titrated should be swirled without splashing to mix the reagents. Initially, most students are tentative and add titrant too slowly for maximum efficiency. With a little practice one can detect the nearness of the end point by the fact that the indicator change fills more of the solution after a drop of titrant is added and the color change takes longer to disappear.
End points are the points where the color is changing most rapidly with titrant volume.
As the end point is neared the titration should be slowed down drastically, and the walls of the flask should be washed down with distilled water to make sure that all materials are mixed. It is possible to add much less than one drop of material by rapidly turning the stopcock through wide open. Alternatively, open the stopcock just enough to form the beginning of a drop on the end of the buret, and then close the stopcock. Then touch the tip to the side of the vessel into which you are titrating, and wash it into the solution with a bit of DI water. At the end point, read the buret again to 0.01 mL with the precautions previously described.