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.

20. Suppose that during Reaction 2 with a magnetic field, the magnetic field had been removed at time = 10 min. Five minutes later, at time = 15 min, the % PM would most likely have been:

Answer and Explanation

Your Answer is

Correct Answer is G

Explanation

It can be seen from figure 2 that the MP% is higher without magnetic field, so follow the steps described in the question stem, and at 15 minutes, %MP should be between the with magnetic field and without magnetic field at this time That is 30%-60%