Analytical Procedures: Cupric Chloride Working Solution

(Courtesy Great Western Chemical Company)

Copper Analysis:

a. Pipette a 1.0 ml. sample of cupric chloride etching solution into a 250 ml. Erlenmeyer flask. For best accuracy a "To Contain" (TC) pipette is recommended. After dispensing cupric solution from pipette wipe down the exterior of the pipette and rinse out the interior with DI water into the sample flask-total DI water addition should be approximately 50 ml.

b. Add 1-3 ml. of 28% ammonium hydroxide to a deep blue color. Upon color change add a couple extra drops for confirmation of saturation.

c. Add 1-3 ml. of concentrated acetic acid to a clear light blue solution. Upon color change add a couple extra drops for confirmation of saturation.

d. Add 4-5 grams potassium iodide to a dark almost transparent brown-again, excess is preferred.

e. Titrate with 0.10 normal sodium thiosulfate to a clear "water" color.

Calculations:

Copper by ounces per gallon=  ml. sodium thiosulfate x 6.354 / 7.5

ANALYSIS FOR FREE ACID NORMALITY

1. Put 10 ml etchant into 200 ml beaker.
2. Add 40 ml DI water. If solution becomes turbid (cloudy) stop normality is <= 0.005N.
3. If solution is clear blue titrate with 0.1N Sodium Hydroxide (NaOH). Add 0.1N NaOH until turbid (cloudy). Normality is milliliters of NaOH divided by 100.
Example: If 3 ml of NaOH is required, Normality is 0.03N
Note: Solution becomes turbid when hydroxide (OH) ions are available to bond with the CuCl2. This occurs at 2.9 pH. None of the common color indicators work accurately because the critical pH is 2.4 – 2.9 and a large amount of OH is absorbed by the CuCl2 without a change in pH.