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VOL. 9, NO. 6
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE 111. SOLUBILITY OF ZINC IN ELECTROLYTE
TABLE IV. EFFECTOF NITRATEIONS
Zinc Taken
Zinc Found
Zinc Loss
Gram
Gram
Uram
SBC.
Nos Moles/l.
0.1994 0.2001 0,2036 0.2037
0.1956 0.1946 0.1937 0,1901
0.0038 0.0055 0,0099 0.0136
30 60 90 120
0,001 0.0001
Immersion Time
Table IV shows that the nitrate-ion concentration may be as large as 0.001 M without interfering with the determination. For the complete deposition of copper from nitrate solutions, the addition of urea has been suggested ( 7 ) . When urea is added to the zinc electrolyte it not only fails to improve the deposition but actually results in an even larger negative error; therefore urea must not be present in the electrolyte. .The determination of zinc in alloys frequently involves the previous determination of nickel as nickel dimethylglyoxime. has been learned that this reagent must not be present, since a concentration as low as 0.002 M causes a large negative .error, which could not be prevented by heating with concentrated sulfuric acid to sulfur trioxide fumes. Of the more common metals aluminum, chromium, magnesium, and tin do not interfere with the deposition. Antimony and arsenic prevent complete deposition, while bismuth, cadmium, cobalt, copper, iron, lead, manganese, mercury, nickel, and silver are .deposited with the zinc. In each experiment 0.050 gram of foreign metal was added to a 0.2-gram sample of zinc.
Recommended Procedure Prepare a zinc sulfate solution free from heavy metals except ,aluminum, chromium, magnesium, and tin. To this solution, ‘containedin a volume of about 175 ml., add 1.5 grams of citric ,acid arid sufficient 40 per cent sodium hydroxide to make the solution mutral or very slightly acid to methyl red-methylene blue. Dilute the solution to 200 ml. and electrolyze for 1.5 t o 2.0 hours or until the addition of 0.5 ml. of saturated hydrogen sulfide water to 1 ml. of the electrolyte produces not more than a faint opalescence. Use a copper or copper-plated gauze cathode and a rotating platinum anode. The current density should be 1 ampere per sq. dm. To prevent mechanical loss of the solution, the beaker should be covered with a split watch glass. Wash the deposit carefully as it is being removed from the electrolyte, dip into acetone, dry at 86” C., and weigh.
Zinc Taken
Zinc Found
Error
Uram
Gram
Gram
0.2035 0.2038 0.1993 0.2010
0.0088 0.2021 0.1994 0.2008
-0.1947 -0.0017 f0.0001 -0.0002
Appearance Localized Good Good Good
The method has been successfully used by college sophomores for the determination of zinc in brass.
Summary Zinc may be determined quantitatively by e1,ectrodeposition from an acid sulfate solution containing 0.0375 mole per liter of citric acid if the pH is between 4 and 5. With a current density of l ampere per sq. dm. deposition is complete in 1.5 hours. Nitrate ions, dimethylglyoxime, urea, and the following foreign metals interfere with the deposition: antimony, arsenic, bismuth, cadmium, cobalt, copper, iron, lead, manganese, mercury, nickel, and silver. No interference is caused by ammonium ions, aluminum, chromium, or tin.
Literature Cited (1) Nickolls, L. C., and Gaskin, J. G. N., Analyst, 59, 391 (1934). (2) Parodi, G., and Mascazzini, A., G a m chim. ital., 7, 169 (1877). (3) Sand. H. J. S.. and Smallev. William. Chem. News. 103. 14 (1911).
