When one drop more NaOH is added than is required to react with the KHP in a sample, the sample becomes basic and the indicator changes color.
However, this, being only 0. In this experiment, you did things differently. We take the point where the indicator color first appears as an indication that we have added NaOH in an equivalent amount to the KHP present in the sample.
Calculate an average acid molarity using the two closest values. Another error was caused by the deviation in the mass of KHP. The volume of the 50 mL buret used in titration was recorded to the 0. The titrations had to be done with much care and precision because of its sensitivity.
The percentage uncertainty calculated of the concentration of NaOH was 2. The average molarity of sodium hydroxide calculated from step before was multiplied by the volume of the titrating solution added and converted into mols of potassium hydrogen phthalate in the sample. The difference in mass before and after you removed the first sample is, of course, the mass of the first sample itself.
If the calculated acid concentrations from the first and second titrations vary by more than 0. Add 3 to 4 drops of phenolphthalein indicator to the KHP solution in the Erlenmeyer flask.