Analysis & replenishment of passivation solution for stainless steel

A. There's a problem here: acid and dichromate should always decrease with use. How did the bath get too high? Are the analyses being performed properly - verify your numbers before you do anything. I say this because to fix the immediate problem, you'll have to decant part the bath - do the math to figure out how much to decant - and add back purified water. You may also need to add back one of the two components if they weren't out of spec to the same degree.

A. Here are the two analyses with calculations for a Type II, QQ-P-35C [link is to free spec at Defense Logistics Agency, dla.mil], passivation solution.

SCOPE: To determine the concentration of Sodium Dichromate in a solution.

EQUIPMENT:

2 mL Pipet
25 mL Buret
250 mL Erlenmeyer Flask
Deionized Water
0.1 N Sodium Thiosulfate
100 mL Graduated Cylinder
0.5% Starch Indicator
10 mL Graduated Cylinder
Concentrated Sulfuric Acid
10% w/v Potassium Iodide
1.000-1.250 Hydrometer
500 mL Graduated Cylinder

PROCEDURE:
Using the pipet, transfer 5 mL of the sample into the Erlenmeyer flask. Using the graduated cylinder, add 100 mL deionized water to the flask. Using the graduated cylinder, add 5 mL concentrated sulfuric acid and 10 mL potassium iodide solution to the flask. Titrate with 0.1 N sodium thiosulfate until the solutions turns to a straw color. Add 2 mL starch indicator to the flask and continue to titrate until the blue-black color disappears. Record the mL used as V1. Place 500 mL of sample in the graduated cylinder. Measure the density of the solution with the hydrometer. Record this value as"P".

CALCULATION:
C1= (V1*F1*N1)/P
C1 = Concentration of Sodium Dichromate in %w/w.
V1 = mL of sodium thiosulfate used in the titration
F1 = 2.483
N1 = Normality of sodium thiosulfate used in the titration.
P = Density of the solution

REPLENISHMENT:

W1 = P*V2
W2 = (C1/100)*W1
W3 = (C2/100)*W1
W4 = W3-W2
V3 = W4/453.6

P = Density of the solution.
V2 = Volume of the solution in milliliters.
W1 = Weight of the solution in grams.
C2 = Optimum concentration of Sodium Dichromate %w/w.
C1 = Actual Concentration of Sodium Dichromate in %w/w.
W2 = Weight of Sodium Dichromate in solution in grams.
W3 = Optimum weight of Sodium Dichromate in grams.
W4 = Weight of Sodium Dichromate to add in grams.
V3 = Weight of Sodium Dichromate to add in pounds.

DILUTION:

W1 = P*V2
W2 = (C1/100)*W1
W3 = (C2/100)*W1
W5 = W2-W3
W6 = (W5*100)/C1
V4 = W6 / P
V5 = V4 / 3785

P = Density of the solution.
V2 = Volume of the solution in milliliters.
W1 = Weight of the solution in grams.
C2 = Optimum concentration of Sodium Dichromate %w/w.
C1 = Actual Concentration of Sodium Dichromate in %w/w.
W2 = Weight of Sodium Dichromate in solution in grams.
W3 = Optimum weight of Sodium Dichromate in grams.
W5 = Weight of Sodium Dichromate to remove in grams.
W6 = Weight of solution to be removed in grams.
V4 = Volume of solution to be removed in milliliters.
V5 = Volume of solution to be removed in gallons.

and,

SCOPE: To determine the concentration of Nitric Acid in a solution.

EQUIPMENT:

5 mL Pipet
25 mL Buret
250 mL Erlenmeyer Flask
Deionized Water
1.0 N Sodium Hydroxide
100 mL Graduated Cylinder
0.1% Methyl Orange Indicator Solution

PROCEDURE:
Using the pipet, transfer 5 mL of the sample into the Erlenmeyer flask. Using the graduated cylinder, add 100 mL deionized water to the flask. Add 5-10 drops of the Methyl Orange indicator to the diluted sample. Titrate with 1.0N sodium hydroxide. The solution will change colors from orange-red to yellow. Record the mL used as V1.

CALCULATION:

C1= V1*F1*N1
C1 = Concentration of Nitric acid in %v/v.
V1 = mL of sodium hydroxide used in the titration
F1 = 1.27
N1 = Normality of sodium hydroxide used in the titration.

REPLENISHMENT:

W1= [(C2-C1)*V2] / 100
W1 = Gallons of Nitric acid to add to the tank
C2 = Optimum concentration of Nitric acid in %v/v.
C1 = Concentration of Nitric acid in %v/v.
V2 = Operating volume of tank in gal.

DILUTION:

V3 = [(C1-C2)*V2] / C1
V3 = Gallons of solution to remove from the tank
C2 = Optimum concentration of Nitric acid in %v/v.
C1 = Concentration of Nitric acid in %v/v.
V2 = Operating volume of tank in gal.

I assume the formatting will be correct as I cut and pasted the required information.

Best of Luck,

"Equipment 2 ml pipette ..."
"Using the pipette transfer 5 ml ..."

I think any auditor would raise an eyebrow.

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Ed. note: Indeed if that isn't a typo it certainly conjures a humorous procedure :-)

A. The correct sample size for the Sodium Dichromate titration procedure should be 2 ml and not 5 ml.