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.

23. Suppose that Figure 1 had instead been plotted as percent of metal oxide (% MO) versus time:

％ MO =

Which of the following graphs best shows how Figure 1 would have appeared?

Answer and Explanation

Your Answer is

Correct Answer is A

Explanation

If the ordinate in figure 1 is changed to %MO, then it should be 100% at the beginning of the reaction, and the final reaction is 0%, excluding C & D;

You can see it in the original picture The reaction is faster under the condition of the solid line with magnetic field, so the %MO drops to 0 first with the magnetic field (solid line), so choose A