Oxidation State

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SAT Subject Test in Chemistry › Oxidation State

Questions 1 - 2

What is the oxidation number of nitrogen in ?

Explanation

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 $1+x+3\times(-2)=0$ . Solving this gives , so the oxidation number of nitrogen is in this molecule.

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 $\text{Al}^{3+}$ ion would undergo reduction to form $\text{Al}$ metal

BECAUSE

II: reduction is a loss of electrons

T, F

T, T, CE

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

F, F

F, T

Explanation

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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