Chemical Analysis of Cyanide Cadmium Plating Baths

Table 10 lists analytical tests that may be applied to cyanide cadmium plating baths to determine their contents of cadmium metal, sodium cyanide, sodium hydroxide, and sodium carbonate.

Table 10 Analytical tests for determining concentration of selected chemical constituents of cyanide cadmium plating baths

Test constituent

Component

Cadmium metal

Sodium cyanide (total)

Sodium Hydroxide

Sodium Carbonate

Reagents

Hydrochloric or sulfuric acid (concentrated) Ammonium hydroxide (concentrated) Eriochrome black "T" indicator (0.5% solution in alcohol)

Formaldehyde (8% solution in water)

Ammonium hydroxide (concentrated) Potassium iodide (10% solution in water) Silver nitrate (13 g/L, or

LaMotte sulfo-orange indicator Sulfuric acid, standard (0.94

Barium chloride (10% solution in water)

Methyl orange-xylene cyanole

Disodium dihydrogen ethylenediaminetetraacetate dihydrate (EDTA), 0.575M solution (21.4 g/L, or 2.85 oz/gal)

1.7 oz/gal solution in water)

N

indicator solution Hydrochloric acid, standard (0.7 N)

Procedure

1. Pipette exactly 2 mL (0.07 oz) of plating bath into a 250 mL (8.5 oz) Erlenmeyer flask, and dilute to about 100 mL (3.4 oz) with distilled water.

2. Neutralize this dilution to a faint white precipitate with hydrochloric or sulfuric acid. This can be conveniently done from the burette of standard sulfuric acid (0.94 N used for the caustic titration, or by the addition of a 50% solution of hydrochloric acid from an eyedropper. If no precipitate appears, as may happen with a new bath, thymolphthalein can be used as an indicator and will change from blue to colorless on neutralization.

3. Add 10 mL (0.34 oz) of concentrated ammonium

hydroxide and about 4 mL of Eriochrome indicator.

4. Zero the burette.

5. Add 8 mL (0.27 oz) of 8% formaldehyde solution.

6. Titrate immediately with EDTA solution. The color change is from red to blue, and it is sharpest when the solution is titrated as soon as possible after the formaldehyde has been added. A rapid titration will also give a sharper end point. Occasionally, the presence of impurities in the bath will prevent the attainment of a clear blue end point, but the color will prevent the attainment of a clear blue end point, but the color change is still sharp, from a red to a purplish blue.

1. Pipette a 2 mL (0.07 oz)sample of plating bath into a 250 mL (8.5 oz) flask.

2. Add to the sample about 50 mL (1.7 oz) distilled water, 5 to 7 mL (0.17 to 0.24 oz) of ammonium hydroxide, and 2 to 3 mL (0.07 to 0.10 oz) of potassium iodide solution.

3. Titrate with silver nitrate solution to the first stable faint

1. Pipette 10 mL (0.34 oz) of the plating bath into a 250 ml (8.5 oz) flask.

2. Add to the sample about

oz) of indicator solution.

3. Titrate with the sulfuric acid to the color change from orange to yellow.

1. Pipette 10 mL (0.34 oz) of plating bath into a 250 mL (8.5 oz) beaker, add to it about 100 mL (3.4 oz) of water, and heat to boiling.

2. Stir into boiling bath dilution about 20 mL of barium chloride solution; cover mixture; allow to stand warm for

3. Filter, using No. 41 Whatman filter paper, and wash precipitate and flask at least 2 or 3 times with hot distilled water.

4. Place paper and precipitate in the original beaker, add about 10 mL (0.34 oz) of hot distilled water and 3 or 4 drops of indicator.

5. Titrate with the hydrochloric acid (while stirring) to the first permanent color change from green to purple.

yellowish turbidity.

Calculation

Milliliters of EDTA solution used x 0.432 = ounces per gallon, cadmium metal

Milliliters of silver nitrate used x 0.5 = ounces per gallon, total sodium cyanide

Milliliters of sulfuric acid used x 0.5 = ounces per gallon, sodium hydroxide

Milliliters of hydrochloric acid used x 0.5 = ounces per gallon, sodium carbonate

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