Furthermore, we should add distilled water follow up calculation. For instance, the volume of distilled water to be added = 53.9973 ml. (we should add distilled water about 53.9 ml.). If we add distilled water about 54 ml, the concentration is low than we require. In titration of unknown samples, the unknown sample changed from colorless to pink but just a minute it become colorless again. So, we must make sure that it changes from colorless to pink and after let it about 30 second color did not fade out. This is occurred error.