Determination of Free Acidity as Hydrochloric Acid in Ferric Chloride Solution (RDM-5006)
Procedure for Analysis
Theory:
Ferric iron is complexed with Potassium Fluoride to prevent hydrolysis. The free acid is then titrated with standard Sodium Hydroxide to an electrometric end point.
Reagents Required:
- Sodium Hydroxide, standard 0.10N solution.
- 33% Potassium Fluoride (anhyd), or 50% KF.2H2O neutralized to Phenolphthalein endpoint.
- Methanol
Equipment Required:
- pH meter, preferably with electrode that can tolerate immersion in HF
- magnetic stirrer
- Buret
Procedure:
- 1. In 150 ml beaker, weigh accurately 1-2 grams of ferric chloride solution. Add 50 ml Methanol.
- 2. Add 25 ml of Potassium Fluoride solution and mix.
- 3. Put pH probe into solution, and note initial reading, may use either pH or mVolt readings.
- 4. Titrate with standard NaOH until readings increase dramatically, noting pH meter reading after each aliquot of NaOH is added.
- 5. Plot mls NaOH added vs meter readings. Note mls added in area of greatest change of readings, use these mls for calculation below.
Calculation:
% Free acidity as HCl = mls 0.1N NaOH x 0.3645 grams of sample
RD Chemical presents these procedures in good faith, based on laboratory and field testing. Ultimate responsibility for propriety of use, however, must rest with the purchaser and user. RD Chemical Company recommends thorough testing of its products and procedures before use.