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Chloride Ion Analysis

Chlorine, in the form of chloride ions, is present in the bath to increase the conductivity of the bath and to promote the formation of a layer of black oxide on the anodes. This layer increases the efficiency of the anodes in sourcing copper and helps to regulate the amount of copper in the bath.

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

Equipment Required:

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

Reagents Required:

  • 0.2256N Mercuric nitrate
  • Low range chloride test solution (a.k.a. silver nitrate solution)
  • Nitric acid 1:1

Procedure:

  1. Measure 20.0 ml of bath into the 125 ml titration flask, using the graduated cylinder. Add deionized water to the 50 ml mark.
  2. Add 5 ml of CONCENTRATED Nitric Acid or 10 ml of 1:1 Nitric Acid and heat the flask until it is very warm to the touch. (about 45 degrees C).

    GLOVES, APRON AND FACE SHIELD SHOULD BE WORN
    WHEN HANDLING THE FLASK AND THE CONCENTRATED ACIDS.
  3. When the solution has reached temperature, add three to five drops of Low Range Chloride Test Solution using the dropper provided. A white turbidity (cloudiness) will form if chloride is present. Heating the solution just prior to titration will help sharpen the point at which the turbidity disappears and will lead to more consistent results.
  4. Titrate the sample using the 0.2256N Mercuric Nitrate until the turbidity just disappears. Record the number of digits required reach the endpoint (titrator reading denoted NumChlor).

The Chloride Ion content in parts per million (PPM) can be found by:

miligrams per Liter Chloride Ion (or ppm)= NumChlor/2

If the count is less than 100, chlorine should be added in the form of 35% Hydrochloric Acid (HCL) using the formula (target = 60ppm for bath volume = V liters):

35% HCl needed (mL) = { [0.12848 - (0.00107 x NumChlor)] x V }

Example: If a 50 Liter bath titrates to a value of NumChlor = 40, the total amount of 35% HCl needed would be:

{ [0.12848 - (0.00107 x 40)] x 50 } = 4.28 mililiters (cubic centimeters) of 35% HCl

The acceptable range of NumChlor is:

Optimum Range (ppm): 40 to 80 (0.04 to 0.08 g Cl ion per liter)
NumChlor: 80 to 160

CAUTION
Always use the proper attire as outlined above in the SAFETY section when handling concentrated hydrochloric 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.



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