Question

In each of the following reactions, identify which species is the oxidizing agent. a. \(2 \mathrm{Al}(s)+6 \mathrm{HCl}(a q) \rightarrow 2 \mathrm{AlCl}_{3}(a q)+3 \mathrm{H}_{2}(g)\) b. \(\mathrm{Cu}(s)+\mathrm{H}_{2} \mathrm{SO}_{4}(a q) \rightarrow \mathrm{CuSO}_{4}(a q)+\mathrm{H}_{2}(g)\)

Short answer

In reaction a, the oxidizing agent is HCl. In reaction b, the oxidizing agent is H2SO4.

Step-by-step solution

In order to identify the oxidizing agent, we need first to determine the oxidation states of the elements in both given reactions. For reaction a: \(2 \mathrm{Al}(s)+6 \mathrm{HCl}(a q) \rightarrow 2 \mathrm{AlCl}_{3}(a q)+3 \mathrm{H}_{2}(g)\) Oxidation states: Al: 0 (pure element) H: +1 (hydrogen generally has +1 oxidation state when combined with non-metals) Cl: -1 (halogens generally have -1 oxidation state when combined with metals) For reaction b: \(\mathrm{Cu}(s)+\mathrm{H}_{2} \mathrm{SO}_{4}(a q) \rightarrow \mathrm{CuSO}_{4}(a q)+\mathrm{H}_{2}(g)\) Oxidation states: Cu: 0 (pure element) H: +1 (hydrogen generally has +1 oxidation state when combined with non-metals) S: +6 (sulfur in sulfate ion SO4^2- has +6 oxidation state) O: -2 (oxygen generally has -2 oxidation state when combined with other elements) #Step 2: Determine the changes in the oxidation states and identify the oxidizing agent#

In this step, we will compare the initial and final oxidation states in each reaction to identify changes (reduction or oxidation), and from these changes, identify the oxidizing agent. For reaction a: Al changes from 0 to +3 (oxidation) H changes from +1 to 0 (reduction) Since Cl remains the same, the oxidizing agent must be a species that contains Cl.

The oxidizing agent in reaction a#

HCl is the oxidizing agent in reaction a. For reaction b: Cu changes from 0 to +2 (oxidation) H changes from +1 to 0 (reduction) Since both S and O remain the same, the oxidizing agent must be a species that contains H.

The oxidizing agent in reaction b#

H2SO4 is the oxidizing agent in reaction b.

Key concepts

Redox Reactions

Understanding redox reactions is crucial for students tackling chemistry homework, as they often lay the foundation for more complex topics. Redox, a shorthand for reduction-oxidation, involves the transfer of electrons between two substances. It's essential to remember that reduction refers to the gain of electrons, while oxidation means the loss of electrons.

Consider a simple example: when a substance loses electrons, it's said to be oxidized, while the substance that gains those electrons is reduced. This transfer cements the redox transaction, and we can observe these changes through the alteration of oxidation states. In the context of the exercise problem, Al and Cu are oxidized as they lose electrons while the hydrogen in HCl and H₂SO₄ is reduced, receiving electrons.

Oxidation States

When examining redox reactions, the concept of oxidation states, or oxidation numbers, becomes a critical tool. The oxidation state tells us about the degree of oxidation of an atom in a compound. For instance, in a pure element like Al(s) or Cu(s), the oxidation state is zero since the atoms are not combined with others to which they can either lose or gain electrons.

• In compound forms, such as HCl(aq), AlCl₃(aq), or CuSO₄(aq), each atom has a specific oxidation state that reflects its electronic environment.
• For hydrogen, this state is typically +1 (except in metal hydrides where it's -1), and for oxygen, it's usually -2, unless in peroxides or bonded with fluorine.

Identifying these states is key to disclosing who the electron donor and acceptor are in a reaction – a necessary step for pinpointing the oxidizing agent.

Chemical Education

Chemical education provides students with the systematic methods required to understand and solve chemical problems, like identifying an oxidizing agent within a reaction. By thoroughly examining the changes in oxidation states, learners gain the ability to analyze reactions beyond surface level.

As educators, it's paramount to express these complex ideas clearly and step-by-step, to foster a solid foundational knowledge in students. Doing so involves breaking down the principles of chemical changes and explaining the importance of each component within a reaction. When students understand why and how an oxidizing agent, such as HCl or H₂SO₄, functions to drive the redox process, they are better equipped to engage with and solve chemical equations effectively and confidently.