CHEMICAL REACTION BETWEEN METALLIC MAGNESIUM AND AQUEOUS SALT SOLUTIONS
QUANTITATIVE PART, 11
1930 Volume 16 Issue 10 Pages 1057-1063
Details
1930 Volume 16 Issue 10 Pages 1057-1063
Metals of the alkali and alkaline earth groups react with dilute acids according to the following equation
Below 10-3 normal, this reaction does not proceed and the reaction of the second kind alone takes place as follows:
This means that metal atom reacts directly with water molecule (Molecular reaction). In the case of magnesium, this molecular reaction was not decisively proved, but it seems very probable that equation (2) does also exist, because magnesium behaves, in many properties, quite similarly to alkaline earth elements. These were the conclusions of the previous paper.
Thus, the view that chemical reaction between magnesium and aqueous salt solutions is due to the interaction between Mg atom, H2O molecule and Cl- ion was proved not unreasonable, yet, it was not quite clear whether H+ ion does participate in the reaction mechanism or not. The present paper deals with this important question. The reaction mechanism itself is moreover discussed in some details. The experiments were carried out on solutions with various [H+], keeping [Cl-] always constant and equal to IO-2 normal. The reaction velocity diminishes with diminution of [H+], but does not vanish when [H+] becomes zero, leaving very large velocity. The velocity remains constant between [H+]=10-4 and 10-11, being perfectly independent of H+ ion Therefore, we can conclude that some reaction other than (I) is taking place, While the (I) reaction accelerates considerably when the solution is stirred, as may be expected, the reaction below [H+]=10-4 retards very nuch. This fact also confirms the existence of some reaction different from (1). Taking these experimental facts into consideration we must conclude the existence of the fundamental reaction (2). for magnisium Stirring effect was explained by assuming the auto-catalitic action of some intermediate compound. The minimum point in the velocity-log [H+] curve can also be explained by this theory.
In conclusion, the author put forward the theory that Mg atom, H2O molecule and Cl- ion react each other forming some unknown intermediate compound, which decomposes on accumulating, giving off H2 gas and regenerating Cl- ion. The reaction accelerates when the compound accumulates around the specimen but retards when it is scattered away by stirring. H+ ion does not take part in the reaction mechanism.
