Question

Is this reaction a redox reaction? Explain your answer. $$ 2 \mathrm{NaCl}(\mathrm{aq})+\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq}) \rightarrow 2 \mathrm{NaNO}_{3}(\mathrm{aq})+\mathrm{PbCl}_{2}(\mathrm{~s}) $$

Short answer

No, this reaction is not a redox reaction; the oxidation states of all elements remain unchanged.

Step-by-step solution

Define Redox Reaction

A redox (reduction-oxidation) reaction is a chemical reaction in which one element loses electrons (oxidation) and another element gains electrons (reduction). To determine if a reaction is a redox reaction, we must check whether there is a change in the oxidation states of the elements involved.

Determine Oxidation States of Reactants

For the reactants, let's find the oxidation states: In NaCl, Na has an oxidation state of +1 and Cl is -1. In Pb(NO₃)₂, Pb is typically +2, while within the nitrate ion (NO₃⁻), each oxygen is -2 and nitrogen is +5.

Determine Oxidation States of Products

For the products: In NaNO₃, Na is +1, each oxygen is -2, and nitrogen is +5. In PbCl₂, Pb is still +2 and each Cl is -1. Thus, there is no change in the oxidation states in the products compared to the reactants.

Analyze Changes in Oxidation States

Compare the oxidation states of each element in reactants and products. The oxidation states of Na, Cl, Pb, N, and O do not change from reactants to products, suggesting that electrons were neither lost nor gained by any of the elements.

Conclusion

Since the oxidation states of the elements remain constant from reactants to products, there is no transfer of electrons. Therefore, this reaction does not involve any reduction or oxidation.

Key concepts

Oxidation States

The concept of oxidation states is essential in understanding redox reactions. Oxidation states are imaginary charges that atoms would have if all bonds were ionic. They provide a way to keep track of electron transfer in chemical reactions.
In a typical molecule, such as NaCl, oxidation states help us see that sodium (Na) has an oxidation state of +1 and chlorine (Cl) an oxidation state of -1. The sum of the oxidation states for a neutral compound is zero. For polyatomic ions, the total charge of the ion is the sum of the oxidation states.
Identifying these oxidation states allows us to track changes in a reaction, determining if electrons are transferred.

Chemical Reaction Analysis

Analyzing a chemical reaction involves examining the chemical equations to determine if it's a redox reaction. In any reaction, elements can change partners as molecule bonds break and form.
For example, in the given reaction of NaCl with Pb(NO₃)₂, the equation provides a straightforward swapping of components. This involves the trading of partners between reactants and products without altering oxidation states.
This step is crucial to establish the type of reaction and understand whether different processes, like oxidation and reduction, occur.

Electron Transfer

Electron transfer is the movement of electrons from one atom or molecule to another, and it is a defining characteristic of redox reactions. In these reactions, one substance loses electrons (is oxidized) and another gains them (is reduced).
However, for the given reaction of NaCl and Pb(NO₃)₂, all elements maintain their oxidation states. Sodium remains +1, chlorine remains -1, and lead remains +2 through the process. This lack of change indicates no electron transfer occurs in the reaction.
Understanding electron transfer is essential for distinguishing chemical reactions that involve redox processes from those that do not.

Reduction and Oxidation Processes

Reduction and oxidation processes are two halves of a redox reaction. Oxidation involves the loss of electrons, increasing an atom's oxidation state, while reduction involves the gain of electrons, decreasing an atom's oxidation state.
In the exercise, each element has the same oxidation number both before and after the reaction. This suggests that the oxidation state of Na, Cl, Pb, N, and O does not change, indicating the absence of oxidizing and reducing actions.
Understanding these concepts helps clarify why some reactions do not qualify as redox, such as when no net electron transfer is observed.