How to prepare and Standardize 0.5 N Sodium hydroxide volumetric solution

How to prepare and Standardize 0.5 N Sodium hydroxide volumetric solution.

                                                                       

Preparation of 0.5 N Sodium hydroxide  Volumetric solution.

➤ Glass ware and instruments required.

Beaker, Glass stirrer, Graduated Pipettes, Graduated cylinder, Analytical balance, Sucker, Volumetric flask, Fume hood.

 ➤ Reagents required.

Sodium hydroxide.
Molecular wt NaOH , 40.0
Potassium hydrogen phthalate primary standard. (Previously dried for 2 hour at 120°C)
Phenolphthalein indicator.

➤ Preparation.

Weigh 22 g sodium hydroxide pallets reagent grade in beaker, add 150 ml of  carbon dioxide free water. Cool to room temperature. Filter through filter paper and transfer to 1000 ml volumetric flask. Dilute up to the mark with same solvent and transfer to tight polyolefin container. 

➤ Standardisation.

Accurately weigh about 2.5 g potassium hydrogen phthalate PS, previously crushed lightly and dried for 2 hour at 120°C, in 250 ml conical flask. Dissolve in 100 ml carbon dioxide free water. Add 2 drops of phenolphthalein indicator solution. Titrate with 0.5 N / 0.5 M sodium hydroxide till the solution becomes permanent pink. Note this final end point as burette reading in ml.

➤ Calculations.

                               g  KHC₈H₄O₄  x  0.5

N / M = --------------------------------------------------

                            0.1021  x   Burette reading in ml