Predict the products of the following reactions and balance...

Predict the products of the following reactions and balance the equations. (a) Zn is added to a solution of $\mathrm{Cr}_{2}\left(\mathrm{SO}_{4}\right)_{3}$ in acid. (b) $\mathrm{FeCl}_{2}$ is added to a solution containing an excess of $\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}$ in hydrochloric acid. (c) $\mathrm{Cr}^{2+}$ is added to $\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}$ in acid solution. (d) $\mathrm{Mn}$ is heated with $\mathrm{CO}_{3}$ . (e) $\mathrm{CrO}$ is added to 2 $\mathrm{HNO}_{3}$ in water.

Predict the products of the following reactions and balance the equations.
(a) Zn is added to a solution of $\mathrm{Cr}_{2}\left(\mathrm{SO}_{4}\right)_{3}$ in acid.
(b) $\mathrm{FeCl}_{2}$ is added to a solution containing an excess of $\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}$ in hydrochloric acid.
(c) $\mathrm{Cr}^{2+}$ is added to $\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}$ in acid solution.
(d) $\mathrm{Mn}$ is heated with $\mathrm{CO}_{3}$ .
(e) $\mathrm{CrO}$ is added to 2 $\mathrm{HNO}_{3}$ in water.

Key Concepts

Redox Reactions

This concept covers chemical reactions where electrons are transferred between species. In the reactions presented, a change in the oxidation states of the metals and nonmetals indicates that oxidation (loss of electrons) and reduction (gain of electrons) processes are occurring simultaneously. Understanding redox reactions is fundamental to predicting products when reactive metals or ions interact in solution or under heat.

Activity Series

The activity series is a ranking of metals (and some nonmetals) based on their tendency to be oxidized, which is vital when predicting displacement reactions. By consulting this series, one can infer whether a more reactive metal will reduce the ion of a less reactive metal and displace it from its compound, an idea that underpins several of the provided reactions.

Oxidation States

Determining the oxidation states of elements in compounds is crucial for understanding electron transfer during redox reactions. By assigning oxidation numbers, one can track how electrons are redistributed throughout the reaction, which helps in identifying which species are oxidized and which are reduced, as well as in balancing the overall reaction.

Half-Reaction Balancing

This method involves separating a redox reaction into oxidation and reduction halves, balancing each for mass and charge, and then combining them into a balanced overall reaction. It is especially useful in acid (or basic) solutions where additional species like H+ or OH– need to be balanced alongside the electrons, as seen in several parts of the problem.

Comproportionation/Disproportionation Reactions

These terms describe reactions in which an element undergoes both oxidation and reduction simultaneously to form a product with an intermediate oxidation state (comproportionation) or where a single species forms two different oxidation states (disproportionation). Recognizing such processes is key in predicting outcomes when species can react with themselves or similar species, particularly in systems involving multiple oxidation states of the same element.

Acid-Catalyzed Redox Chemistry

Many of the reactions occur in an acidic medium, which not only provides H+ ions to assist in balancing redox reactions but can also influence the reaction pathways. Acidic conditions can promote the formation of certain products by stabilizing intermediate species or shifting the equilibrium of redox reactions, an important consideration when predicting the reaction outcomes.

Thermal Reactions in Solids

When a metal is heated with a nonmetallic compound like a carbonate, the reaction may involve solid-state redox processes and thermal decomposition. Understanding how heat can drive oxidation-reduction reactions and induce the decomposition of compounds, such as releasing gases or forming new oxides, is essential for predicting the products of these high-temperature reactions.

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