Determination of Free Acid in Ferric Etchants (RDM-5001)
Theory:
Ferric Chloride is reduced with Sodium Thiosulfate to Ferrous, allowing titration of HCl without interference.
Equipment Required:
- Balance, Top loading
- Beaker 250 ml
- Magnetic Stirrer Plate
- Graduate 100 ml
- Magnetic Stirrer Bar
- Plastic Beaker 50 ml
- Burette 50 ml
- Disposable Pipettes
Reagents Required:
- Copper Sulfate 10% solution (CuSO45H2O - 100 grams per liter)
- Sodium Thiosulfate Anhydrous (Na2S2O3)
- Sodium Hydroxide 0.100 N
- Hydrochloric Acid 0.100 N
- MO-XC Indicator mixture
(0.8 grams Xylene Cyanole FF;
0.6 grams Methyl Orange;
95 ml Methanol;
Deionized water to 1000 ml).
Procedure:
- Weigh 7.0 ± 0.5 grams Na2S2O3 into a 250 ml beaker.
- Add 100 ml of water, 1 ml of 10% CuSO45H2O, 1 ml Indicator mixture.
- Neutralize with 0.1N HCl from green to gray (do not record amount).
- Weigh ≈10.2 grams of etchant into 50 ml plastic beaker.
- Transfer weighted etchant to neutralized thiosulfate solution.
- Titrate with 0.1N NaOH to green If solution is already green, acid is essentially zero
Calculations:
Mls 0.1N NaOH x 3.45 = % Free HCl
weight of sample