Chemical Analysis - Water Analysis in a "Peroxy-sulfuric" Copper Etching Bath

Equipment Required:

• Titration flask (125 ml)
• 10 ml Automatic pipettor
• Digital titrator

Reagents Required:

• Ferroin indicator
• 0.50N Cerric solution

Procedure:

1. Measure 30 mL of deionized water into the titration flask. This will constitute the analysis environment and as such the measured quantity is not critical.
2. Add one drop of Ferroin indicator.
3. Using the automatic pipetter, add 0.10 mL of sample etchant. Swirl the flask around to mix the solution thoroughly. The mixture should be bright orange in color.
4. Using the digital titrator, titrate with the .50N Cerric until the solution goes from orange to colorless (or light blue). Record the number of drops of titrant used as indicated on the digital readout (denote the digital titrator reading NumPerox).
5. If NumPerox is less than 503 drops, the hydrogen peroxide (H₂O₂) content of the bath must be adjusted. Assuming a bath volume of V liters, the amount needed to raise the concentration to the optimum 10% (vol) may be calculated using:

Liters of 50% H₂O₂ needed = (0.10-.0001788 x NumPerox) x V

Or, if you are using H₂O₂ with a concentration different than 50% (wt.), use the formula:

Liters of H₂O₂ needed ={(0.05-.0000894 x NumPerox) x V} / concentration of H₂O₂ (wt.)

Note: If you are using a bath based on the FT-2 catalyst system, you should replenish the FT-2 in concert with any addition of H₂O₂. To replenish FT-2 use:

Liters of FT-2 needed = 0.33 x liters of 50% H₂O₂ added

To express the concentration of H₂O₂ (100%) as a percent of bath volume, use:

% H₂O₂ = .00894*(NumPerox)

The acceptable range of digital titrator readings for total hydrogen peroxide content is:

Acceptable Range (%): 4 to 5.5

NumPerox: 447 to 615

Example: A reading of 350 drops would indicate that the addition of approximately 1.4 liters of 50% H₂O₂ would be sufficient to return a 38 liter bath to its original peroxide level.

CAUTION:

Always use the proper attire as outlined above in the SAFETY section when handling concentrated sulfuric acid. If contact should occur, flush affected area with cool tap water for 15 minutes. CONTACT A PHYSICIAN IMMEDIATELY.

HANDLE WITH CARE:

Always wear protective clothing, acid resistant gloves, and a full coverage face shield when handling this or any other corrosive material.