Standardization of NaOH

What is the point of this experiment? The purpose of this lab is to find out the exact concentration of NaOH solution. In order to know that, the solution needs to be standardized. The exact concentration must be determined by titrating a known mass of a primary standard acid with the NaOH solution. With the known concentration of NaOH we are able to calculate the concentration of unknown acids.

Primary Standard Primary standard is a substance used to determine the concentration of a solution. A primary standard should be: - Available in pure form - Be stable at room temperature - Easy to dry - Have high equivalent weight to minimize weighing errors - Hydrophobic – should not easily absorb H2O when exposed to air Commonly used primary standard for NaOH is Potassium Hydrogen Phthalate (KHP)

KHC8H4O4(aq) + NaOH(aq) -> H2O(l) +Na (aq) + K ^+(aq) + C8H4O42-(aq) Indicator used: Phenolphthalein When excess acid is present, the color of the solution is colorless When excess base is present, phenolphthalein anion predominates and we observe a permanent color change to pink at the endpoint.

Endpoint Endpoint is achieved when the solution turns from colorless to pink color It is important to go slowly towards the end of the titration Successful endpoint is achieved when one drop of base from buret turns the solution pink Since we know the mass of KHP we can calculate the moles of acid. At endpoint moles of acid = moles of base With endpoint volume of the base and moles of the base we can calculate the concentration of the NaOH