ADA Practice Exam question 51

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This is question #51 from the ADA practice exam...I dont understand what they are asking for? Redox reaction? Thanks for the help. BTW the answer is C.

51. During a titration it was determined that
30.00 mL of a 0.100 M Ce4+ solution was
required to react completely with 20.00
mL of a 0.150 M Fe2+ solution. Which
one of the following reactions occurred?

A. Ce4+ + 3Fe2+ + H2O 3Fe3+
+ CeO- + 2H+
B. 2Ce4+ + Fe2+ Fe4+ + 2Ce3+
C. Ce4+ + Fe2+ Fe3+ + Ce3+
D. Ce4+ + 2Fe2+ 2Fe3+ + Ce2+
E. Ce4+ + 2Fe2+ 2Fe4+ + Cs2+
+ 2e-

 

[ucla2134]

This is question #51 from the ADA practice exam...I dont understand what they are asking for? Redox reaction? Thanks for the help. BTW the answer is C.

51. During a titration it was determined that
30.00 mL of a 0.100 M Ce4+ solution was
required to react completely with 20.00
mL of a 0.150 M Fe2+ solution. Which
one of the following reactions occurred?

A. Ce4+ + 3Fe2+ + H2O 3Fe3+
+ CeO- + 2H+
B. 2Ce4+ + Fe2+ Fe4+ + 2Ce3+
C. Ce4+ + Fe2+ Fe3+ + Ce3+
D. Ce4+ + 2Fe2+ 2Fe3+ + Ce2+
E. Ce4+ + 2Fe2+ 2Fe4+ + Cs2+
+ 2e-

This one is a redox reaction. They gave u the information that the mole between the 2 half reactions are equal, meaning that the number of electrons lost from one species must gain by another species. Only B satisfy.

Let's break the reaction into half:
2Ce4+--> 2Ce3+
The Ce go from 8+ to 6+, it gain 2 electrons or reduced. Thus, the reducing agent Fe must lost 2 electron. As we saw,
Fe2+-->Fe4+ ---> the Iron species lost 2 electrons, which then reduce the Ce from 8+ to 6+.
Thus the electrons are balance.
Hope this helps!

 

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hey thanks for the reply it helped!