Question

Is each of the following substances likely to serve as an oxidant or a reductant: (a) \(\mathrm{Ce}^{3+}(a q)\), (b) \(\mathrm{Ca}(\mathrm{s})\), (c) \(\mathrm{ClO}_{3}^{-}(a q)\), (d) \(\mathrm{N}_{2} \mathrm{O}_{5}(g)\) ?

Short answer

(a) \(\mathrm{Ce}^{3+}(a q)\): Oxidant, (b) \(\mathrm{Ca}(\mathrm{s})\): Reductant, (c) \(\mathrm{ClO}_{3}^{-}(a q)\): Oxidant, (d) \(\mathrm{N}_{2} \mathrm{O}_{5}(g)\): Oxidant.

Step-by-step solution

Identify the Substances and Their Oxidation States

(a) \(\mathrm{Ce}^{3+}(a q)\): Cerium ion with an oxidation state of +3. (b) \(\mathrm{Ca}(\mathrm{s})\): Calcium(solid) with an oxidation state of 0. (c) \(\mathrm{ClO}_{3}^{-}(a q)\): Chlorate ion with Chlorine having an oxidation state of +5. (d) \(\mathrm{N}_{2} \mathrm{O}_{5}(g)\): Dinitrogen pentoxide with Nitrogen having an oxidation state of +5.

Consider Oxidation and Reduction Possibilities

Now we will consider whether the given oxidation state is more likely to be oxidized or reduced. (a) Cerium is a rare-earth metal and prefers to have an oxidation state of +4 in its most stable state. It is already at a +3 state. So, it is most likely to accept an electron and increase its oxidation state to +4. (b) Calcium is an alkaline earth metal and easily loses its 2 valence electrons to have a stable +2 oxidation state. Currently, at an oxidation state of 0, it is more likely to lose electrons and reduce. (c) The Chlorine in the chlorate ion is already at a high oxidation state of +5. It can accept an electron to reduce its oxidation state to +4 (found in \(\mathrm{ClO}_{2}^{-}\)). So, it is more likely to serve as an oxidant. (d) Nitrogen in N₂O₅ is also at its highest oxidation state, +5. Nitrogen can accept an electron to lower its oxidation state or gain more electrons to form nitrogen gas (N₂). Thus, it is also more likely to serve as an oxidant.

Determine if the Given Substance is an Oxidant or a Reductant

(a) \(\mathrm{Ce}^{3+}(a q)\): Oxidant (it is more likely to gain an electron and increase its oxidation state). (b) \(\mathrm{Ca}(\mathrm{s})\): Reductant (it is more likely to lose electrons and decrease its oxidation state). (c) \(\mathrm{ClO}_{3}^{-}(a q)\): Oxidant (it is more likely to gain an electron and decrease its oxidation state). (d) \(\mathrm{N}_{2} \mathrm{O}_{5}(g)\): Oxidant (it is more likely to gain an electron and decrease its oxidation state).

Key concepts

Oxidation States

Understanding oxidation states is crucial when studying chemical reactions in chemistry. An oxidation state is the hypothetical charge an atom would have if all bonds to atoms of different elements were completely ionic. A common misconception is that all atoms in a molecule have a charge, but in reality, oxidation states are used as a bookkeeping tool to determine electron transfer during a reaction.

To determine oxidation states, there are rules chemists follow. For instance, the oxidation state of an atom in its elemental form is zero. In a compound, hydrogen typically has an oxidation state of +1, oxygen is usually -2, and other elements have oxidation states according to their group number in the periodic table. Taking calcium (Ca) as an example, as it's an alkaline earth metal, in its solid form, it naturally exists with a zero oxidation state. However, it tends to lose electrons to attain a +2 oxidation state, which corresponds to a more stable electronic configuration.

Oxidant and Reductant Identification

In chemical reactions, the ability to identify an oxidant and a reductant is essential to understand the transformation of substances. An oxidant, also known as an oxidizing agent, gains electrons and is reduced in the process. Conversely, a reductant, or reducing agent, loses electrons and is oxidized. This can be remembered through the mnemonic 'LEO says GER': Lose Electrons Oxidation, Gain Electrons Reduction.

Applying this knowledge to the given exercises, we can categorize \( \mathrm{Ce}^{3+}(a q) \) as an oxidant because it has a +3 oxidation state and can gain an electron to reach the more stable +4 state, characterizing it as electron-accepting or oxidizing. On the other hand, calcium (Ca) in its elemental form serves as a reductant, as it readily loses electrons to achieve a lower energy oxidation state. This insight is not only crucial to solve textbook exercises but also serves as a fundamental concept in predicting the outcomes of real-world chemical processes.

Chemical Reactions

Chemical reactions involve the transformation of substances through the breaking and forming of chemical bonds. Understanding how to discern the role of different compounds in a chemical reaction is fundamental. Oxidation and reduction are processes that go hand in hand: when a substance is oxidized, another must be reduced, creating an oxidation-reduction (redox) reaction.

Oxidation involves the loss of electrons, while reduction means the gain of electrons. In the context of our exercise, \( \mathrm{N}_{2} \mathrm{O}_{5}(g) \) serves as an oxidant, as the nitrogen seeks to lower its high +5 oxidation state, suggesting that it may gain electrons from the reductant in the course of a reaction. When these reactions occur, energy is often either absorbed or released, and this drives the chemical processes we observe, from the rusting of iron to the metabolism of food in our bodies.