Question

Indicate each of the following as an oxidation or a reduction: a. \(\mathrm{Na}^{+}(a q)+e^{-} \longrightarrow \mathrm{Na}(s)\) b. \(\mathrm{Ni}(s) \longrightarrow \mathrm{Ni}^{2+}(a q)+2 e^{-}\) c. \(\mathrm{Cr}^{3+}(a q)+3 e^{-} \longrightarrow \mathrm{Cr}(s)\) d. \(2 \mathrm{H}^{+}(a q)+2 e^{-} \longrightarrow \mathrm{H}_{2}(g)\)

Short answer

a, c, d: Reduction; b: Oxidation.

Step-by-step solution

Identify the gain or loss of electrons in reaction (a)

In the reaction \[\begin{equation}\mathrm{Na}^{+}(a q)+e^{-} \longrightarrow \mathrm{Na}(s)\text{,}\end{equation}\]the \( \mathrm{Na}^{+} \) ion is gaining one electronto form \( \mathrm{Na}(s) \).Since gaining electrons refers to a reduction,this process is a reduction.

Identify the gain or loss of electrons in reaction (b)

In the reaction \[\begin{equation}\mathrm{Ni}(s) \longrightarrow \mathrm{Ni}^{2+}(a q)+2 e^{-}\text{,}\end{equation}\]\( \mathrm{Ni}(s) \)is losing two electrons to form\( \mathrm{Ni}^{2+}(a q) \). Since losing electrons refers to an oxidation, this process is an oxidation.

Identify the gain or loss of electrons in reaction (c)

In the reaction \[\begin{equation}\mathrm{Cr}^{3+}(a q)+3 e^{-} \longrightarrow \mathrm{Cr}(s)\text{,}\end{equation}\]the \( \mathrm{Cr}^{3+} \) ion is gaining three electrons to form \( \mathrm{Cr}(s) \). Since gaining electrons refers to a reduction, this process is a reduction.

Identify the gain or loss of electrons in reaction (d)

In the reaction\[\begin{equation}2 \mathrm{H}^{+}(a q)+2 e^{-} \longrightarrow \mathrm{H}_{2}(g)\text{,}\end{equation}\]the \( \mathrm{H}^{+} \) ions are gaining electrons to form\( \mathrm{H}_{2}(g) \). Since gaining electrons refers to a reduction, this process is a reduction.

Key concepts

Electron Transfer

Electron transfer is a fundamental concept in chemistry, especially in redox reactions. It involves the movement of electrons from one species to another. In the context of redox reactions, one molecule or atom will lose electrons while another molecule or atom will gain those electrons. This transfer of electrons results in changes in the oxidation states of the participating species. Understanding electron transfer is key to grasping more complex chemical reactions.
For instance, in the equation \( \text{Na}^{+}(aq) + e^{-} \rightarrow \text{Na}(s) \), the sodium ion (\( \text{Na}^{+} \)) gains one electron (\

Gain of Electrons

When a substance gains electrons during a chemical reaction, it undergoes a process known as reduction. Reduction is always associated with a decrease in the oxidation state of the substance. For example, in the reaction \( \text{Cr}^{3+}(aq) + 3e^{-} \rightarrow \text{Cr}(s) \), the chromium ion (\

Redox Reactions

Redox reactions are a type of chemical reaction that involves the transfer of electrons between two species. The term 'redox' stands for reduction-oxidation. In a redox reaction, one species is oxidized (loses electrons) and another is reduced (gains electrons). Understanding redox reactions can help explain a range of processes in both chemistry and biology. Redox reactions can be seen in various everyday processes such as combustion, respiration, and even photosynthesis. For example, consider the reaction \( 2\text{H}^{+}(aq) + 2e^{-} \rightarrow \text{H}_{2}(g) \), here hydrogen ions (\