Passage IV

If a metal oxide sample at high temperature is exposed to a stream of H2 gas, it may be converted to a pure metal. Reactions 1-3 are examples of this process for a cobalt oxide and 2 different iron oxides, respectively.

Reaction 1: CoO + H2 → Co + H2O

Reaction 2: FeO + H2 → Fe + H2O

Reaction 3: Fe3O4 + 4H2 → 3Fe + 4H2O

During the reaction, the H2 stream carries away H2O, so the resulting sample is composed of metal oxide and pure metal only.

Figures 1-3 show how the percent of pure metal, ％ PM, in metal oxide samples changed over time as they underwent Reactions 1-3, respectively, with and without a magnetic field present.

％ PM =

Figure 1 adapted from M. W. Rowe et al., "Effect of Magnetic Field on Reduction of Cobalt Oxides." @1979 by Chapman and Hall Ltd.

Figures 2 and 3 adapted from M. W. Rowe, S. M. Lake, and R. Fanick, "Effect of Magnetic Field on Reduction of Iron Oxides: Magnetite and Wüstite." @1977 by Macmillan Magazines Ltd.

21. According to Figure 3, in Reaction 3, how did the addition of a magnetic field affect the yield of pure Fe metal? At 20 min, the yield obtained with a magnetic field was about:

Answer and Explanation

Your Answer is

Correct Answer is D

Explanation

Look directly at figure 3 and look at the solid line with magnetic field. When the abscissa time is 20 minutes, the ordinate MP% is close to 100, which means that it is basically pure metal Fe at this time;

< p>Compared with without magnetic field, at 20 minutes, the ordinate is about 50, so with is twice as long as without