SAT II Chemistry : Oxidation State

Study concepts, example questions & explanations for SAT II Chemistry

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Example Questions

Example Question #1 : Oxidation State

What is the oxidation number of nitrogen in ?

Possible Answers:

Correct answer:


First, note that the molecule does not have a charge, meaning that the oxidation numbers of each atom must add up to zero. Hydrogen has an oxidation number of  and oxygen has an oxidation number of . Thus, if we call the oxidation number of nitrogen , we can get the equation . Solving this gives , so the oxidation number of nitrogen is  in this molecule.

Example Question #2 : Oxidation State

The following is a modified true/false question. In it, you must decide if each individual statement is true (T) or false (F). If both are true, then you must also decide if the second statement is a correct explanation (CE) of the first statement.

I: An  ion would undergo reduction to form  metal


II: reduction is a loss of electrons

Possible Answers:

F, T

T, T (Statement II is not a correct explanation of Statement I)

F, F

T, T, CE

T, F

Correct answer:

T, F


Statement II is false: reduction is a gain of electrons. Looking at statement I, the ion's charge would decrease by 3 in becoming a metal, which suggests that the ion gains 3 electrons. Thus, it is undergoing reduction.

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