Page 97 - QRedition5.0 062021

Quality Requirements Edition 5.0 European Enamel Association

8.2.1.3 Determination of bivalent iron, sulphuric acid pickling 8.2.1.4 Determination of nickel sulphate, nickel-exchange bath

Purpose and scope Purpose and scope
Too high a content of iron (II)-sulphate can lead to a crystallizing pickling bath while cooling In order to guarantee an even nickel deposition the concentration of nickel sulphate is
down. The concentration of iron in pickling baths has to be checked regularly. to be kept constant.

Analysis instructions Analysis instructions:
0
5 ml of a cooled (20 C) sample of the pickling bath solution is to be mixed with about 100 25 ml of a cooled (20 C) sample of the nickel bath is to be diluted with about 100 ml distilled
0
ml distilled water and 10 ml Reinhardt-Zimmermann-solution in an Erlenmeyer flask and water in an Erlenmeyer flask. After about 20 ml ammonium chloride solution has been
titrated under strong agitation with 0.1 n KMnO -solution. The titration is brought to an end
4 added, it has to be mixed with a triethanolamine solution. This solution has to be slightly
when after the last addition of potassium permanganate the solution still shows after one acidic so that the masking of iron by triethanolamine can be realized. If necessary some
minute a light pink. drops of hydrochloric or sulphuric acid can be used for adjustment. The slight acidic

solution is to be set ammoniacal with about 25 ml ammonia and after the addition of Murexid
ml consumption 0.1 n KMnO4 x 1.1 = g Fe / l pickling solution titrate with:
2+

0.1 m Complexon-III-solution until the colour changes from brownish pink to deep violet.
Required reagents:
Reinhardt-Zimmermann-solution:
ml consumption 0.1 m Complexon-III-solution x 1.1 = g NiSO x 7H O / l nickel
67 g MnSO x 4 H O, 138 ml H PO (density 1.70) and 4 2
4 2 3 4 bath solution
130 ml H SO ( density 1.82 ) are to be filled up with 1000 ml distilled water.
2 4 Required reagents:
0.1 n potassium permanganate solution
Ammonium chloride
54 g NH Cl per liter
4
Ammonia 25 %, p.a.
Triethanolamine - solution
TriEthanol diluted in water in a proportion 1 : 1

Murexid
Murexid is mixed with NaCl in a proportion 1 : 200

0.1 m Complexon-III-solution
Complexon-III-solution is the bisodium salt of the ethylenediaminetetra
acetic acid (mol. weight 372.1) and is known under the trade name

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Titriplex (Merck) and Idranal (Riedel de Haen)
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