Question

Balance this equation and classify it as combination, decomposition, single- replacement, or double-replacement: \(\mathrm{K}_{2} \mathrm{CrO}_{4}+\mathrm{Al}\left(\mathrm{NO}_{3}\right)_{3} \rightarrow \mathrm{Al}_{2}\left(\mathrm{CrO}_{4}\right)_{3}+\mathrm{KNO}_{3}\)

Short answer

The balanced equation is: \(2\left(\mathrm{K}_{2}\mathrm{CrO}_{4}\right)+3\left(\mathrm{Al}\left(\mathrm{NO}_{3}\right)_{3}\right)\rightarrow \mathrm{Al}_{2}\left(\mathrm{CrO}_{4}\right)_{3}+6\left(\mathrm{KNO}_{3}\right)\). This reaction is classified as a double-replacement reaction.

Step-by-step solution

Identify all reactants and products

In the given equation, the reactants are potassium chromate (\(\mathrm{K}_{2}\mathrm{CrO}_{4}\)) and aluminum nitrate (\(\mathrm{Al}\left(\mathrm{NO}_{3}\right)_{3}\)). The products are aluminum chromate (\(\mathrm{Al}_{2}\left(\mathrm{CrO}_{4}\right)_{3}\)) and potassium nitrate (\(\mathrm{KNO}_{3}\)).

Balance the equation

To balance the equation, we will find the correct coefficients for each compound so that the number of atoms of each element is the same on both sides of the equation. 1. Aluminum (\(\mathrm{Al}\)): There are 1 \(\mathrm{Al}\) in aluminum nitrate and 2 \(\mathrm{Al}\) in aluminum chromate. To balance these, we need to multiply aluminum nitrate by 2: \(2\left(\mathrm{K}_{2}\mathrm{CrO}_{4}\right)+3\left(\mathrm{Al}\left(\mathrm{NO}_{3}\right)_{3}\right)\rightarrow \mathrm{Al}_{2}\left(\mathrm{CrO}_{4}\right)_{3}+k\left(\mathrm{KNO}_{3}\right)\) 2. Potassium (\(\mathrm{K}\)): There are 2 \(\mathrm{K}\) in potassium chromate and 1 \(\mathrm{K}\) in potassium nitrate. To balance these, we need to multiply potassium nitrate by 6: \(2\left(\mathrm{K}_{2}\mathrm{CrO}_{4}\right)+3\left(\mathrm{Al}\left(\mathrm{NO}_{3}\right)_{3}\right)\rightarrow \mathrm{Al}_{2}\left(\mathrm{CrO}_{4}\right)_{3}+6\left(\mathrm{KNO}_{3}\right)\) Now the balanced equation is: \(2\left(\mathrm{K}_{2}\mathrm{CrO}_{4}\right)+3\left(\mathrm{Al}\left(\mathrm{NO}_{3}\right)_{3}\right)\rightarrow \mathrm{Al}_{2}\left(\mathrm{CrO}_{4}\right)_{3}+6\left(\mathrm{KNO}_{3}\right)\)

Classify the reaction

In this reaction, we have two ionic compounds reacting to form two new ionic compounds by exchanging their partners: - Potassium chromate (\(\mathrm{K}_{2}\mathrm{CrO}_{4}\)) donates its chromate ion (\(\mathrm{CrO}_{4}\)) to aluminum nitrate (\(\mathrm{Al}\left(\mathrm{NO}_{3}\right)_{3}\)), forming aluminum chromate (\(\mathrm{Al}_{2}\left(\mathrm{CrO}_{4}\right)_{3}\)). - Aluminum nitrate (\(\mathrm{Al}\left(\mathrm{NO}_{3}\right)_{3}\)) donates its nitrate ions (\(\mathrm{NO}_{3}\)) to potassium chromate (\(\mathrm{K}_{2}\mathrm{CrO}_{4}\)), forming potassium nitrate (\(\mathrm{KNO}_{3}\)). This type of reaction is called a double-replacement reaction.

Key concepts

Double-Replacement Reaction

Understanding double-replacement reactions is essential when studying chemistry. In such reactions, two ionic compounds exchange their ions, forming two new compounds in the process. This can be visualized as a dance between four atoms, where two pairs switch partners.

For instance, when a solution of potassium chromate mixes with a solution of aluminum nitrate, each compound parts with one of their ions: the chromate (\( \text{CrO}_4^{2-} \) ion) pairs up with aluminum ions to form aluminum chromate, while the nitrate (\( \text{NO}_3^- \) ion) joins forces with potassium ions, yielding potassium nitrate. The general form is AB + CD to yield AD + CB, where A and C are cations, and B and D are anions.

Double-replacement reactions often occur in aqueous solutions, where the ions can move freely and interact. These reactions are pivotal in various fields, including biology where they are essential for processes like nerve signaling and homeostasis.

Chemical Reaction Classification

Chemical reaction classification is akin to organizing a vast library of books—each book (reaction) has its own place based on its genre (reaction type). The main types include synthesis (combination), decomposition, single-replacement, and double-replacement reactions.

A synthesis reaction combines simple substances to make a more complex one. In decomposition, the opposite happens—a complex substance breaks into simpler parts. During a single-replacement reaction, one element displaces another in a compound. Finally, double-replacement reactions involve the exchange of parts between two compounds, as seen in our previous example.By categorizing reactions, chemists can predict the products and devise methods to create valuable substances effectively. When students can classify a reaction, they understand the core patterns of chemical behavior and can navigate complex chemical equations with ease.

Stoichiometry

Stoichiometry is the mathematics behind chemistry. It's a method for quantifying the relationships between the amounts of reactants and products in a chemical reaction. To balance a chemical equation, one must ensure that the number of atoms for each element is the same on both sides, adhering to the Law of Conservation of Mass.

The process starts with writing a skeletal equation, reflecting unbalanced numbers of atoms. Next, you assign coefficients—the numerical multipliers placed in front of compounds—to achieve a balance. Sometimes this involves simple arithmetic, other times, a trial-and-error approach is necessary. Correct stoichiometry ensures the reaction 'accounting' is precise—no more atoms are spent or created than were present initially.

Mastering stoichiometry equips you with the ability to predict product yields, calculate reactant quantities needed for specific product amounts, and conversely, determine the amount of product formed from given reactants, which is invaluable in both laboratory work and industrial chemical processes.