Question

Write a balanced equation for each of the following single-replacement reactions: (a) Copper wire is placed in an aluminum nitrate solution. (b) Aluminum wire is placed in a copper(II) nitrate solution.

Short answer

(a) No reaction; (b) \( 2 \text{Al} + 3 \text{Cu(NO}_3\text{)}_2 \rightarrow 2 \text{Al(NO}_3\text{)}_3 + 3 \text{Cu} \).

Step-by-step solution

Identify the Reaction Type

Both reactions are single-replacement reactions, where one element replaces another in a compound.

Determine the Reactants for Reaction (a)

For reaction (a), the reactants are copper wire, represented as Cu, and aluminum nitrate, represented as Al(NO_3)_3.

Predict the Products for Reaction (a)

In reaction (a), copper (Cu) attempts to replace aluminum (Al) in the compound. However, copper is less reactive than aluminum, so no reaction occurs. The balanced equation is simply:\[\text{No reaction}\]

Determine the Reactants for Reaction (b)

For reaction (b), the reactants are aluminum wire, represented as Al, and copper(II) nitrate, represented as Cu(NO_3)_2.

Predict the Products for Reaction (b)

In reaction (b), aluminum, being more reactive, replaces copper in copper(II) nitrate to form aluminum nitrate and copper metal. The products are Al(NO_3)_3 and Cu.

Write the Balanced Equation for Reaction (b)

The balanced equation for reaction (b) involves balancing aluminum, copper, and nitrate ions:\[2 \, \text{Al} + 3 \, \text{Cu(NO}_3\text{)}_2 \rightarrow 2 \, \text{Al(NO}_3\text{)}_3 + 3 \, \text{Cu}\]

Key concepts

Single Replacement Reactions

In a single replacement reaction, one element replaces another within a compound. This type of reaction generally occurs between a free element and a compound, resulting in the ion of the free element swapping places with one ion in the compound. Think of it like a game of musical chairs, where one dancer (element) leaves and another takes their place.

In the context of our exercise, we explore reactions between metals and compounds of metals. Here's how it works:

• A metal will replace another metal in a compound if it is more reactive or has a higher position in the reactivity series.
• If the free metal is less reactive, then no reaction occurs, as the compound's metal holds its position. This is demonstrated in the reaction involving copper and aluminum nitrate.
• For aluminum and copper(II) nitrate, aluminum is more reactive, thus it successfully takes copper's place, demonstrating a classic single replacement reaction.

Understanding these basics helps in predicting the outcomes of similar chemical reactions.

Balancing Chemical Equations

Balancing chemical equations is crucial to ensure the law of conservation of mass is satisfied. This law states that matter can neither be created nor destroyed in a chemical reaction, which means the amount of each element must be equal on both sides of the equation.

Here are some steps to successfully balance a chemical equation:

• Write down the unbalanced equation, ensuring all reactants and products are correctly represented.
• Identify the different elements present in the reactants and products.
• Balance each element systematically, using coefficients to adjust the number of atoms on each side of the equation, starting with the most complex molecule.
• Check your work to ensure that the equation is balanced in terms of both atoms and charge.

In our exercise, the equation for the aluminum and copper(II) nitrate reaction was balanced by adjusting coefficients: \[2 \, \text{Al} + 3 \, \text{Cu(NO}_3\text{)}_2 \rightarrow 2 \, \text{Al(NO}_3\text{)}_3 + 3 \, \text{Cu}\]. This ensures the conservation of Al, Cu, and NO₃ ions.

Reactivity Series

The reactivity series is an arrangement of elements, primarily metals, based on their tendency to react. Elements higher in the series are more reactive, meaning they have a stronger ability to displace other elements in chemical reactions, especially during single replacement reactions.

This hierarchy matters because:

• More reactive metals will replace less reactive metals in compounds.
• The reactivity series helps predict whether a single replacement reaction will occur.
• Understanding the series provides insights into the behavior of elements during reactions, which is integral for predicting and balancing chemical equations.

In our examples, aluminum is above copper in the reactivity series, which explains why it can displace copper in copper(II) nitrate but not the other way around. The ability to predict reaction feasibility using the reactivity series is invaluable in practical chemistry.