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SolderOn Acid

If you have not done so, please read the "DOs and DON'Ts section now

Equipment Required:

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

Reagents Required:

  • Deionized water
  • Phenolphthalien indicator
  • 1.60N Sodium hydroxide (titrant)


  1. Measure 30 ml of deionized water into the titration flask. The actual quantity of water is not critical, but too much will make the end point too faint and may result in an erroneous reading.
  2. Using the automatic pipettor, add 1.0 ml of sample solution.
  3. Add 1 to 4 drops of phenolphthalien indicator to the flask. Swirl the flask around to mix thoroughly. The solution will be clear after the addition of the indicator (if there is acid present).
  4. Using the digital titrator, titrate with 1.60N sodium hydroxide until the solution turns red. This is a fairly subtle endpoint, so watch closely.
  5. Assuming that your bath is not excessively depleted of acid, the digital titrator should read at least 600 before you can expect a color change. A bath with the optimum amount of acid present will yield a reading of 821 (± 10).
  6. Record the number of drops of titrant used as indicated on the digital readout.
  7. The amount of SolderOn acid that is needed to replenish the 38 liter (10 gallon) bath can be calculated using the relationship (the digital titrator reading is denoted NUMACID):

SolderOn Acid needed (liters) = (821 - NUMACID) x 0.0106 liters

In imperial units (US gallons), the amount of acid needed is expressed as:

SolderOn Acid needed = (821 - NUMACID) x 0.0028 gal.

To express the concentration of SolderOn acid as a percent of bath volume, use:

% SolderOn acid = 0.0280 x NUMACID

The acceptable range of digital titrator readings is:

Acceptable Range: percent: 20 to 35%
NUMACID: 714 to 1,250


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.


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

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