PREPARATION OF STANDARD SOLUTIONS AND THE DETERMINATION OF THE EQUIVALENT WEIGHT OF AN UNKNOWN SOLID ACID
Purpose of Experiment:
The principle objective of this experiment is to determine the concentration of NaOH and HCl and to prepare standard NaOH and HCl for use in future experiments. NaOH will be standardized against samples of potassium hydrogen phthalate. Concentration of HCl will be determined by using standardized NaOH.
Other objectives include determination of equivalent weight of an unknown solid acid, learning/ reintroducing the physical techniques of dilution and titrating to an indicator end point, to work with equivalents, and basic statistics for reporting experimental results.
Chemical and/or Biochemical Background:
Sodium Hydroxide (NaOH) Hydrochloric acid (HCl)
Potassium Hydrogen Phthalate (KHP) Phenolphthalein (an indicator)
Dilution of NaOH:
NaOH + H2O ( Na+ + OH- + H2O
The equation shows ionization of sodium hydroxide in water. Dissolution of NaOH is highly exothermic.
Standardization of NaOH solution against Potassium acid phthalate (KHP):
NaOH + KHC8O4H4 → KNaC8O4H4 + H2O
Potassium acid Phthalate (weak acid) reacts with OH- from NaOH forming water, and solution is neutralized. Thus the solution turns into pink shown by phenolphthalein, a pH indicator changes its color into pink in pH range of 8.2-10.0.
Dilution of HCl:
HCl + H2O ( H+ + Cl- + H2O
The equation shows ionization of hydrochloric acid in water.
Standardization of HCl solution against standardized NaOH:
NaOH + HCl → NaCl + H2O
Hydroxide ion of known concentration reacts with acid from hydrochloric acid and forms water and salts.
Preparation of 0.1N NaOH:
Weigh about 30g sample of NaOH pellets using an...