and second, in the actual titration,
10FeSO4 + 2KMnO4 + 9H2SO4= 2MnSO4 + 5Fe2(SO4)3 + 2KHSO4 + 8H2O
↓
K = 39
Mn = 55
O4= 64
——
158 × 2 = 316
As before, attention is confined to the two substances under consideration—viz., Fe and KMnO4. In the second equation, we find 316 parts of the permanganate are required for 10 molecules of FeSO4; and in the first equation 56 parts of iron are equivalent to one molecule of FeSO4, therefore 560 of iron are equivalent to 316 of permanganate; and the question is, How much of the permanganate will be equivalent to 20 grams of iron?
560 : 316 :: 20 grams : x.
x = 11.286 grams.
The answer is 11.286 grams.
Very similar to this last problem is the question suggested under the head "Indirect Titration" (p. 43). "If 100 c.c. of the standard permanganate solution are equivalent to 1 gram of iron, how much peroxide of manganese will they be equivalent to?" The equation for dissolving the iron is already given; the second equation is
2FeSO4 + MnO2 + 2H2SO4 = Fe2(SO4)2 + MnSO4 + 2H2O
↓
Mn = 55
O2 = 32
——
87
It will be seen that 87 grams of peroxide of manganese are equivalent to 112 grams of iron. How much then is equivalent to 1 gram of iron?
112 : 87 :: 1 gram : x
x = 0.7767 gram.
It is sometimes convenient to calculate the formula of a substance from its analysis. The method of calculating is shown by the following example. Required the formula of a mineral which gave the following figures on analysis:—