RD Chemical Company - Manufacturing Chemists

HCl in Ferric Chloride Solutions (RDM-5004)

Procedure for Analysis

Theory:
Ferric Chloride is reduced to Ferrous by addition of Sodium Thiosulfate solution, so that it does not interfere with titration. Solution is then titrated with 0.100N Sodium Carbonate to pH 4.00. Sodium Carbonate will neutralize HCl, but will not precipitate metals present, like NaOH would.

Reagents Required:

Saturated Sodium Thiosulfate solution
0.100N Sodium Carbonate solution
pH 4.0 Buffer

Equipment Required:

5.00 ml volumetric pipet
50 ml buret
pH meter
Magnetic stirrer
250 ml flask

Procedure: This procedure is tricky, and will have to be practiced to get reliable results. The procedure should be done in a flask, rather than a beaker to minimize re-oxidation of the ferric by the air, and this makes it very cumbersome to get the pH probe and the buret tip into the flask while it is being stirred on the magnetic stirrer.

Pipet 5.00 mls of the ferric chloride solution to be tested into flask, dilute to 100 mls with deionized water. Add saturated Sodium Thiosulfate solution, one drop at a time, until solution turns (sort of) clear, and further addition does not produce cause additional brown/black color to form. This will require about 5 mls. (Excess Sodium Thiosulfate will cause titration to be low) Place (standardized) pH meter electrode in solution, and titrate with 0.100N Sodium Carbonate solution to pH 4.00, note mls required.

Calculation:
Grams/liter HCl = mls 0.100N Sod. Carbonate X 0.729 Or: %HCl ≈ mls 0.100N Sodium Carbonate X 0.052

* This procedure originally developed by Buckbee Mears Corp.