The Effect of Various Substances on the Electrolysis of Zinc

The determination of zinc electrolytically is a common method when the percentage of zinc in the sample is smell, in which case the method gives accurate results. When the amount of zinc 1s large, the method of electrolysis has some disadvantages. One disadvantage is that the zinc fells off the electrode after it has been deposited. In an analytical chemistry class at the University of Tennessee, the method of estimating zinc by electrolysis is used. In many cases, even when the percentage of zinc is small, it is difficult to deposit the zinc on the electrode so that it will not fall off before it can be weighed. To improve the situation it is not merely a problem of finding conditions which will result in a firm deposit of the zine, but the deposition must be quantitative, which means that all the zinc and no interfering substances must deposit.

The purpose of this thesis was to study the electrical deposition of zinc with the view of finding some conditions in which the metal could be made to deposit in a firm, compact form on the electrode.

One method used in electrolysing & zinc solution is to deposit the metal from a solution of double ammonium oxylate. The zinc separates quickly from this solution but it will not adhere to the electrode. The author found that as much as ten per cent of the zinc fell from the electrode after it was deposited.

Beilstein and Jawelin precipitated zinc from a solution of potassium zinc cyanide. The solution is treated with NeOH until a precipitate is formed and potassium cyanide is added until it dissolves.! The solution is then electrolysed. This method 1s inconvenient since the solution is heated by the strong electric current which is necessary for reduction and must be kept cool.

Parodi and Mascozzini have a method in which they electrolyse a zinc sulphate solution to which has been added sodium acetate end citric scid.l The author found that the zine deposited with this method was spongy and some of it fell from the electrode.

In the method used at the University of Tennessee, rochelle salts is added to the solution to improve the deposit. This is the method used in various technical laboratories. The author found that rochelle salts also improved the deposit but that much of the zinc failed to stick to the electrode.

Other methods of electrolysing zinc solutions were not convénient enough for ordinary laboratory procedure. What is needed is a simple procedure which can be carried out in an average laboratory without special equipment or expense. The present study has resulted in finding some conditions which are excellent for the deposition of zinc in a compact form on the electrode.