Preparation and standardization of sodium hydroxide

Neutralization of hydronium or hydroxide ion to form water is widely used as the basis for volumetric determinations of acids, bases and salts of weak acids. The reaction is characterized by a rapid change in pH near the equivalence point, a change that is readily detected by an acid-base indicator.
Neutralization titrations are performed with standard solutions of strong acids or strong bases. A standard solution (or standard titrant) is a reagent of exactly known concentration.
Preparation and Standardization of 0.10 M NaOH
1) Boil 500 mL of distilled water and then cool it. Use this distilled water to prepare 100 mL of 0.10 M NaOH solution using 0.400 mg of sodium hydroxide.
2) Transfer 2.0000 to 2.5000 g of potassium hydrogen phthalate (KHC8H4O4/KHP) into a 100 mL Erlenmeyer flask. Dissolve the salt in 50 mL of distilled water and then volume adjusted to 100 ml with distilled water.
3) Transfer 10 ml potassium hydrogen phthalate solution to conical solution and add 5 to 6 drops of phenolphthalein indicator.
3) Titrate the solution with 0.10 M NaOH prepared until a faint pink color appears and persists at least 30 seconds.
4) Repeat the titration with another replicate.
5) Calculate the individual molarity of the NaOH solutions for replicates.

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