Ch.4 - Reactions in Aqueous Solution
Chapter 4, Problem 96a
The commercial production of nitric acid involves the following chemical reactions:
4 NH3(g) + 5 O2(g) → 4 NO(g) + 6 H2O(g)
2 NO(g) + O2(g) → 2 NO2(g)
3 NO2(g) + H2O(l) → 2 HNO3(aq) + NO(g)
(a) Which of these reactions are redox reactions?

1
Identify the oxidation states of each element in the reactants and products for each reaction.
For the first reaction: 4 NH_3(g) + 5 O_2(g) → 4 NO(g) + 6 H_2O(g), determine the change in oxidation states for nitrogen and oxygen.
For the second reaction: 2 NO(g) + O_2(g) → 2 NO_2(g), determine the change in oxidation states for nitrogen and oxygen.
For the third reaction: 3 NO_2(g) + H_2O(l) → 2 HNO_3(aq) + NO(g), determine the change in oxidation states for nitrogen.
Identify which reactions involve a change in oxidation states, indicating they are redox reactions.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Redox Reactions
Redox reactions, or reduction-oxidation reactions, involve the transfer of electrons between substances. In these reactions, one species is oxidized (loses electrons) while another is reduced (gains electrons). Identifying redox reactions requires analyzing changes in oxidation states of the elements involved.
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Oxidation States
Oxidation states (or oxidation numbers) are assigned to atoms in a compound to indicate their degree of oxidation or reduction. The oxidation state helps in determining which atoms are oxidized and which are reduced in a reaction. For example, in the reaction of ammonia with oxygen, nitrogen in NH3 has an oxidation state of -3, which changes to +2 in NO.
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Balancing Chemical Reactions
Balancing chemical reactions is essential to ensure that the number of atoms of each element is conserved throughout the reaction. This involves adjusting coefficients in front of the reactants and products. In redox reactions, balancing also includes ensuring that the total charge is the same on both sides of the equation, which is crucial for identifying the electron transfer.
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Related Practice
Open Question
Suppose you have a solution that might contain any or all of the following cations: Ni2+, Ag+, Sr2+, and Mn2+. Addition of HCl solution causes a precipitate to form. After filtering off the precipitate, H2SO4 solution is added to the resulting solution and another precipitate forms. This is filtered off, and a solution of NaOH is added to the resulting solution. No precipitate is observed. Which of the four ions listed above must be absent from the original solution?
Open Question
You choose to investigate some of the solubility guidelines for two ions not listed in Table 4.1, the chromate ion (CrO₄²⁻) and the oxalate ion (C₂O₄²⁻). You are given 0.01 M solutions (A, B, C, D) of four water-soluble salts: