HIRANUMA APPLICATION DATAPLATING &ETCHING
SOLUTION

Automatic Titrator

Data No.

Feb. 10,2021

E5

Quantitative determination of chromic anhydrideand chromium (III) in chromium plating solution

1. Abstract
The control and analysis of chromium plating solution are very important process for the product quality.
General analytical components of the chromium plating solution are the following 5 components.
(1) Chromic anhydride (CrO3)(2) Chromium (III) (Cr3+)(3) Sulfuric acid
(4) Fluoride ion(5) IronThis report introduces an example of measurement for (1) chromic anhydride and (2) chromium (III).
The measurement procedure of chromic anhydride is as follows: Take diluted sample solution and add
sulfuric acid to acidify it. Accurately add a certain amount of ammonium iron (II) sulfate in an amount sufficient
to react the entire amount of chromic anhydride, and react the chromic anhydride by the reaction formula (1). The
unreacted ammonium iron (II) sulfate is titrated with a potassium permanganate standard solution according toreaction formula (2) to obtain chromic anhydride.
The measurement procedure of chromium (III) is as follows: Take diluted sample solution and add sodiumhydroxide to adjust it to pH 12 or more. Add hydrogen peroxide to oxidize chromium (III) to chromium (VI). Boil
off and degrade the excess hydrogen peroxide by the reaction formula (3). Add sulfuric acid to acidify it.
Accurately add a certain amount of ammonium iron (II) sulfate in an amount sufficient to react the entire amountof chromium (VI), and react the chromium (VI) by the reaction formula (1). The unreacted ammonium iron (II)sulfate is titrated with a potassium permanganate standard solution according to reaction formula (2) to obtaintotal chromium amount in term of chromic anhydride. Chromium (III) is obtained by subtracting chromicanhydride from total chromium amount.
6Fe(NH4)2(SO4)2＋ 2CrO3 ＋ 6H2SO4 →3Fe2(SO4)3 ＋ 6(NH4)2SO4 ＋ Cr2(SO4)3 + 6H2O･･･(1)2KMnO4 + 10FeSO4(NH4)2SO4 ＋ 8H2SO4 →K2SO4 + 2MnSO4 + 5Fe2(SO4)3 ＋ 10(NH4)2SO4+8H2O
2[Cr(OH)4]－ + 3H2O2 + 2OH－ → 2CrO42－ ＋ 8H2O

2. Configuration of instruments and reagents(1) Configuration of instruments
Main unit: Automatic Titrator COM SeriesOption: Optional Buret 1 set

Electrode: Platinum electrode PT-301(Connect to IE-2)

Reference electrode RE-201Z(Connect to RE-2)･･･(2)･･･(3)(2) Reagents
Titrant: 0.02 mol/L potassium permanganate standard solution (For volumetric analysis)

Additive solution : 10 % sodium hydroxide solution: 30 % hydrogen peroxide solution: 3 mol/L sulfuric acid: 0.1 mol/L ammonium iron (II) sulfate solution
Dissolve 40 g of ammonium iron (II) sulfate hexahydrate in 30 mL of 10 % sulfuric
acid solution, and pure water is added to make 1000 mL.

3. Measurement procedure
3.1. Blank measurement(1) Dispense 90 mL of DI water and 10 mL of 3 mol/L sulfuric acid into a 200 mL beaker.
(2) Immerse electrode and start measurement. Firstly dispense 15 mL of 0.1 mol/L ammonium iron (II)sulfate solution with optional buret No.2.
(3) Titrate with 0.02 mol/L potassium permanganate standard solution. The obtained titrant volume is set toblank value of chromic anhydride and chromium (III) measurement.
3.2. Measurement of chromic anhydride(1) Take 1 mL of sample solution into a 50 mL volumetric flask and add DI water to make diluted sample
solution.
(2) Take 1 mL of diluted sample solution into a 200 mL beaker with volumetric pipette. Taking into accountthe dilution ratio, the net sample volume is 0.2 mL.
(3) Add 90 mL of DI water and 10 mL of 3 mol/L sulfuric acid.
(4) Immerse electrode and start measurement. Firstly dispense 15 mL of 0.1 mol/L ammonium iron (II)sulfate solution with optional buret No.2. Then titrate with 0.02 mol/L potassium permanganate standardsolution.
3.3. Measurement of chromium (III)(1) Take 1 mL of diluted sample solution prepared on section 3.2. into a 200 mL beaker with volumetricpipette. Taking into account the dilution ratio, the net sample volume is 0.2 mL.
(2) Add 40 mL of DI water and then add 10 % sodium hydroxide solution to adjust pH 12 or more.
(3) Add 3 mL of 30 % hydrogen peroxide solution.
(4) Add 100 mL of DI water and cover the beaker with watch glass. Heat on a hot plate until the amount ofliquid becomes 100 mL or less.
(5) After cooling to room temperature, rinse the inner wall of the watch glass and beaker with a small amountof pure water, and collect the rinse solution into the beaker. Add 10 mL of 3 mol/L sulfuric acid.
(6) Immerse electrode and start measurement. Firstly dispense 15 mL of 0.1 mol/L ammonium iron (II)sulfate solution with optional buret No.2. Then titrate with 0.02 mol/L potassium permanganate standardsolution.

4. Measurement conditions and results
Examples of titration conditions(1) Blank measurement

Dispense of 0.1 mol/L ammonium iron (II) sulfate
Cndt No.
1Method
DispBuret No.
2S-Timer0 sec
Disp Vol.
15 mL

Titration with potassium permanganate
Cndt No.
2MethodAuto
Buret No.
1Amp No.
2D. Unit
mV
S-Timer
30 secC.P. mL
12 mL
T Timer
30 secD.P. mL
0.5 mLEnd Sens 1000
Over mL
0.2 mL
Max.Vol.
20 mL

ConstantNo.
SizeBlank
Molarity
Factor
KL

20 mL
0 mL
0.02 mol/L
1.000
00UnitFormulaDigitsMode No.
Pre Int
Del K
Del Sens
Int Time
Int Sens
Brt Speed
Pulse

805053240

Mode No.
Pre Int
Del K
Del Sens
Int Time
Int Sens
Brt Speed
Pulse

805053240sec
mVsec
mVmL
D
3(2) Measurement of chromic anhydride

Dispense of 0.1 mol/L ammonium iron (II) sulfate
Cndt No.
1Method
DispBuret No.
2S-Timer
0 sec
Disp Vol.
15 mL

Titration with potassium permanganate
Cndt No.
3Method
AutoBuret No.
1
Amp No.
2D. Unit
mV
S-Timer
0 sec
C.P. mL
0.5 mLT Timer
30 secD.P. mL
0.2 mLEnd Sens 1000
Over mL
0.2 mL
Max.Vol.
20 mL

ConstantNo.
SizeBlank
Molarity
FactorKL

30.2 mL
14.984 mL
0.02 mol/L1.000
166.667
0Unit
FormulaDigitsg/L(B-D)*K*M*F/S
4sec
mVsecmV

(3) Measurement of chromium (III)Dispense of 0.1 mol/L ammonium iron (II) sulfate
Cndt No.
1Method
DispBuret No.
2S-Timer
0 sec
Disp Vol.
15 mL

Titration with potassium permanganate
Cndt No.
3Method
AutoBuret No.
1Amp No.
2D. Unit
mV
S-Timer
0 sec
C.P. mL
0.5 mLT Timer
30 secD.P. mL
0.2 mLEnd Sens 1000
Over mL
0.2 mL
Max.Vol.
20 mL

ConstantNo.
SizeBlank
Molarity
Factor
KL30.2 mL
14.984 mL
0.02 mol/L
1.000
166.667
0Unit
FormulaDigitsg/L(B-D)*K*M*F/S
4ConstantNo.
SizeBlank
Molarity
FactorKL

40.2 mL
0 mL
0 mol/L
1.000
126.130.520

Calculation of chromium (III)
Cndt No.
Method4Calc

Unit
FormulaDigitsg/L(CA-K)*L
4

Mode No.
Pre Int
Del K
Del Sens
Int Time
Int Sens
Brt Speed
Pulse

805053240

sec
mV
secmV

Measurement results
Result of blank
Number ofmeasurement

Titrant
volume (mL)

1215.005
14.962

Statistic
calculationAvg.
SD

14.984 mL
0.030 mL

RSD

0.203 %

Result of chromic anhydride

Number ofmeasurement

Samplesize (mL)

120.2

Titrant
volume (mL)

Chromic anhydride
(g/L)

7.434

125.8347.398

126.434

Statistic
calculation

Avg.
SD
RSD

126.13 g/L
0.42 g/L
0.34 %

Result of chromium (III)
Number ofmeasurement
12

Samplesize (mL)

Titrant
volume (mL)

Total Chromium(g/L as CrO3)

Chromium (III)(g/L as Cr(III))

Statistic
calculation

0.2

7.238
7.223

129.100
129.350

1.5444
1.6744

Avg. 1.61 g/LSD
0.09 g/L
RSD 5.71 %Example of titration curve

Blank

Chromic anhydride

Chromium (III)5. Note(1) Notice on pretreatment
In the measurement of the total amount of chromium, if the residual hydrogen peroxide is not sufficiently
removed by heating after the oxidation of chromium (III) to chromium (VI) by the hydrogen peroxide solution,a positive error will occur in the measurement. To prevent the measurement errors, it is important to performthe sufficient heat treatment to remove hydrogen peroxide.
(2) Notice on back-titration
Since this measurement is performed by back titration, the accuracy of added ammonium iron (II) sulfate
affects the measurement accuracy. In this paper, the accuracy is improved by automatic dispensing withburette.
In addition, ammonium iron (II) sulfate is an unstable reagent that causes a decrease in concentration due tooxidation by air. It is important to check the blank value by performing blank measurement as appropriate.
Keywords：Chromium plating solution, Chromic anhydride, Total chromium, Chromium (III), Chromium (VI)

*Some measurement would not be possible depending on optional configuration of system.