Question

Which of the following are redox reactions? a. \(2 \mathrm{Na}+\mathrm{Cl}_{2} \longrightarrow 2 \mathrm{NaCl}\) b. \(\mathrm{C}+\mathrm{O}_{2} \longrightarrow \mathrm{CO}_{2}\) c. \(2 \mathrm{H}_{2} \mathrm{O} \longrightarrow 2 \mathrm{H}_{2}+\mathrm{O}_{2}\) d. \(\mathrm{NaCl}+\mathrm{AgNO}_{3} \longrightarrow \mathrm{AgCl}+\mathrm{NaNO}_{3}\) e. \(\mathrm{NH}_{3}+\mathrm{HCl} \longrightarrow \mathrm{NH}_{4}+\mathrm{Cl}^{-}\) f. \(2 \mathrm{KClO}_{3} \longrightarrow 2 \mathrm{KCl}+3 \mathrm{O}_{2}\) g. \(\mathrm{H}_{2}+\mathrm{C}_{2} \longrightarrow 2 \mathrm{HCl}\) h. \(\mathrm{H}_{2} \mathrm{SO}_{4}+2 \mathrm{KOH} \longrightarrow \mathrm{K}_{2} \mathrm{SO}_{4}+2 \mathrm{H}_{2} \mathrm{O}\) i. \(\mathrm{Zn}+\mathrm{CuSO}_{4} \longrightarrow \mathrm{ZnSO}_{4}+\mathrm{Cu}\)

Short answer

a, b, c, f, and i are redox reactions.

Step-by-step solution

Understand What a Redox Reaction Is

A redox (reduction-oxidation) reaction involves the transfer of electrons between two species. It involves a change in the oxidation states of the elements involved. In a redox reaction, one substance gets oxidized (loses electrons), and another gets reduced (gains electrons).

Identify Oxidation States

For each reaction, determine the oxidation states of each element before and after the reaction to see if any changes occur.

Analyzing Reaction a

Reaction a: Before reaction:Na (0), Cl (0) After reaction: Na (+1), Cl (-1) Sodium is oxidized (0 to +1), and chlorine is reduced (0 to -1). This is a redox reaction.

Analyzing Reaction b

Reaction b: Before reaction:C (0), O (0) After reaction: C (+4), O (-2) Carbon is oxidized (0 to +4), and oxygen is reduced (0 to -2). This is a redox reaction.

Analyzing Reaction c

Reaction c: Before reaction:H (+1), O (-2) in H2O After reaction: H (0) in H2, O (0) in O2 Hydrogen is reduced (+1 to 0), and oxygen is oxidized (-2 to 0). This is a redox reaction.

Analyzing Reaction d

Reaction d: No change in oxidation states for Na, Cl, Ag, N. This is not a redox reaction.

Analyzing Reaction e

Reaction e: No change in oxidation states for N, H, Cl. This is not a redox reaction.

Analyzing Reaction f

Reaction f: Before reaction:K (+1), Cl (+5), O (-2) in KClO3 After reaction: K (+1), Cl (-1), O (0) in O2 Chlorine is reduced (+5 to -1), Oxygen is oxidized (-2 to 0). This is a redox reaction.

Analyzing Reaction g

Reaction g: There is typographical error and doesn't form redox reaction.

Analyzing Reaction h

Reaction h: No change in oxidation states for H, S, O, K. This is not a redox reaction.

Analyzing Reaction i

Reaction i: Before reaction:Zn (0), Cu (+2) in CuSO4 After reaction: Zn (+2) in ZnSO4, Cu (0) Zinc is oxidized (0 to +2), and copper is reduced (+2 to 0). This is a redox reaction.

Key concepts

oxidation states

Oxidation states, also known as oxidation numbers, are a conceptual tool used to keep track of electron transfer in redox reactions. They represent the hypothetical charges that atoms would have if all bonds were ionic. An element's oxidation state can change during a chemical reaction. For example, in the reaction:
\(2 \mathrm{Na}+\mathrm{Cl}_{2} \longrightarrow 2 \mathrm{NaCl}\onumber\)
Sodium's oxidation state changes from 0 in elemental sodium to +1 in sodium chloride, while chlorine's oxidation state changes from 0 in \(\mathrm{Cl}_{2}\) to -1 in \(\mathrm{NaCl}\). Understanding these changes helps to identify redox reactions.
To determine the oxidation state of an element in a compound, you can use a set of rules:

• The oxidation state of an atom in its elemental form is always 0.
• The oxidation state of a monoatomic ion is equal to its charge.
• Oxygen usually has an oxidation state of -2, except in peroxides or when bonded to fluorine.
• Hydrogen has an oxidation state of +1 when bonded to nonmetals and -1 when bonded to metals.
• The sum of oxidation states in a neutral compound is zero; in a polyatomic ion, it is equal to the ion's charge.

Using these rules, we can track how electrons are transferred in a redox reaction by comparing the oxidation states before and after the reaction.

electron transfer

Electron transfer is the movement of electrons from one atom or molecule to another during a chemical reaction. This process is central to redox reactions. When an atom or molecule loses electrons, it undergoes oxidation. Conversely, when an atom or molecule gains electrons, it undergoes reduction. For instance:
\( \mathrm{C}+\mathrm{O}_{2} \longrightarrow \mathrm{CO}_{2}\)
In this reaction, carbon starts with an oxidation state of 0 and ends at +4, indicating it has lost electrons (oxidized). Meanwhile, oxygen starts with an oxidation state of 0 and ends at -2, indicating it has gained electrons (reduced).
By determining the direction and magnitude of electron transfer, you can identify which substances are oxidized and which are reduced. Electron transfers can be summarized as:

• Oxidation: loss of electrons (increase in oxidation state)
• Reduction: gain of electrons (decrease in oxidation state)

Balancing these electron transfers in redox reactions ensures that the number of electrons lost equals the number of electrons gained, maintaining the conservation of charge.
Understanding electron transfer helps in predicting the products and understanding the mechanism of many chemical processes.

oxidation and reduction

Oxidation and reduction are two complementary processes involved in redox reactions. Oxidation refers to the loss of electrons by a molecule, atom, or ion, which increases the oxidation state of the element involved. Reduction is the gain of electrons by a molecule, atom, or ion, decreasing its oxidation state. These processes always occur together; when one substance is oxidized, another must be reduced.
For example, consider the reaction:
\( \mathrm{Zn} + \mathrm{CuSO}_{4} \longrightarrow \mathrm{ZnSO}_{4} + \mathrm{Cu} \)
Here, zinc starts with an oxidation state of 0 and goes to +2 in \(\mathrm{ZnSO}_{4}\), indicating it is oxidized. Copper in \(\mathrm{CuSO}_{4}\) starts with an oxidation state of +2 and goes to 0 in elemental copper, indicating it is reduced.
To identify oxidation and reduction in a redox reaction, follow these steps:

• Determine the oxidation states of the elements involved before and after the reaction.
• Compare these states to see which have increased (oxidation) and which have decreased (reduction).

Redox reactions are key to many biological processes, industrial applications, and combustion reactions. Understanding them enables you to grasp the essential principles of many chemical reactions.
By mastering the concepts of oxidation and reduction, you can more easily predict and understand complex chemical behaviors.