Example 3.4 Suppose that the mass percent of iron in iron(ll) oxide, Feo, was de
ID: 568397 • Letter: E
Question
Example 3.4 Suppose that the mass percent of iron in iron(ll) oxide, Feo, was determined graphically (like in Figure 3.1) to be 77.7%, and the mass percent of iron in iron(III) oxide, Fe,01, was determined to be 69.9%. The analyses involved reducing the iron oxide to elemental iron by heating the oxide under a flow of hydrogen gas, represented by the following chemical equations: The mass percent of FeO and Fe Os in a mixture of the two oxides can be determined using the weight percentages of each individual oxide. Given a sample of mixed iron oxides, determine the mass percent of iron(ll) oxide, FeO, and iron(III) oxide, Fe,01, present in a sample if the following data was obtained Trial Sample mass (g) 0.750 0.320 1.100 Iron mass (g) 0.557 0.238 0.817 A plot of iron mass on the y-axis and sample mass on the x-axis provides a line whose slope is equal to (g iron)/(g mixture), the mass fraction of iron in the mixture (like the example of Figure 3.1). For the data above, the slope equals 0.742. Remember, we want to find the composition of the mixture, how can we find the amount of FeO and Fe,Os from the slope of the line? The total iron mass is comprised of iron that came from FeO and iron that came from Fe,O3. While we cannot physically or chemically determine which iron atom came from which iron oxide, we can use math to our advantage to theoretically categorize the iron obtained: Based on this, the slope can be "split up g FeFe 0 g mixture g mixture g mixture g mixture This gives a final equation: slope gFereo Fepeo eq. 3.1 g mixture g mixture 45
Explanation / Answer
4)
Since, slope = (x * g Fe / g FeO) + (1-x) g Fe / g Fe2O3
0.7246 = (x * 0.777) + (1-x) * 0.699
0.7246 - 0.699 = 0.078 x
0.0256 = 0.078 x
0.328 = x
Or 32.8 % = x = FeO
Fe2O3 = (1-x)
Fe2O3 =1 - 0.328
Fe2O3 = 0.672
Fe2O3 = 67.2%
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