The Effect of Varying Quantitiesof Manganese Oxide onPotassium Permanganate.
The following experiments were made for the purpose of determining the effect of varying quantities of manganese oxide on the time required for the reduction of potassium permanganate.
A. In the presence of nitric acid.
The ratio of manganese to available oxygen in the material used for these experiments was determined and found to be
1.018 : 1.000
The experiments were conducted after the same manner as those previously described.
Different portions of the manganese oxide were weighed out and treated in the flasks used in the previous experiments with the quantities of permanganate which were found by calculation to have the desired molecular ratios to the oxide.
A quantity of N/10 nitric acid equivalent to the potassium of the potassium permanganate was added. The flasks were then immersed in the bath of boiling water and the time required for the disappearance of the permanganate color noted.
The ratios of the oxide to the permanganate and the times required for the reduction of the latter are embodied in the following table.
The results appearing in the table on the same horizontal lines are those of experiments made simultaneously, that is, the flasks in these experiments were immersed at the same time and in the same water-bath. These, that is the results appearing on the same horizontal line, and these only are comparable, since it was found that very slight differences in the temperature of the bath were of great influence on the length of time required for the reduction of the permanganate.
It is clear that the rate of the reduction of the permanganate is greatly increased by increasing the quantity of the manganese oxide.
After reduction of the permanganate, the contents of the flasks were inevery case filtered and the filtrate tested by Crum’s reaction for the presence of manganese. No manganese was found. The absence of manganese in the filtrate shows that the reduction of the permanganate was not due to the formation of manganese nitrate, though it will be clear from the results of subsequent experiments that the presence of nitric acid exerts an influence on the rate of the reduction.
B. In neutral solution.
The condition were the same as under A, except that the nitric acid was omitted. Those flasks containing potassium permanganate and one, two and seven molecular equivalents respectively of the manganese oxide were immersed in the water-bath as before.
C. In alkaline solution.
The conditions were the same as under B, except that five molecules of potassium hydroxide were added for each molecule of the permanganate.
It appears that potassium permanganate is less easily reduced by manganese oxide in neutral than in acid solutions and in alkaline that in neutral solutions.