rinse down the sides of the flask to make sure that any splattered NaOH get a chance to react.
add the final increment dropwise, or even in half- drops washed from the buret tip with a few drops of water. The endpoint has been reached when a faint pink color persists throughout the mixed solution for about 30 seconds. Dissolving CO2 will produce carbonic acid, which will neutralize the excess NaOH and turn the phenolphthalein colorless if the titration too far overrun. Exercise care to avoid overshooting the endpoint (intense pinkish-red color). If you do accidentally overshoot the endpoint, weigh a fresh sample of KHP and repeat the titration .