Question

Complete and balance each of the following single-replacement reactions: (a) \(\mathrm{Mg}(s)+\mathrm{NiSO}_{4}(a q) \rightarrow\) (b) \(\mathrm{Al}(s)+\mathrm{SnSO}_{4}(a q) \rightarrow\)

Short answer

(a) \(\text{Mg} + \text{NiSO}_4 \rightarrow \text{Ni} + \text{MgSO}_4\) is balanced. (b) 2\(\text{Al} + 3\text{SnSO}_4 \rightarrow 3\text{Sn} + \text{Al}_2(SO_4)_3\) is balanced.

Step-by-step solution

Understand Single-Replacement Reactions

In single-replacement reactions, a more reactive metal displaces a less reactive metal from its compound. This means that the metal in the reactant form (like magnesium in equation (a)) will replace the metal ion in the salt (like nickel in equation (a), which is part of NiSO₄). To determine if the reaction occurs, check the activity series of metals: a metal can only replace another metal if it is higher in the activity series.

Determine Reactivity Using Activity Series

Refer to an activity series of metals, which ranks metals by their reactivity. For reaction (a), magnesium (Mg) is more reactive than nickel (Ni), and for reaction (b), aluminum (Al) is more reactive than tin (Sn). Thus, both reactions will proceed as single-replacement reactions.

Write the Unbalanced Equations

For reaction (a), write the unbalanced equation as \(\text{Mg}(s) + \text{NiSO}_4(aq) \rightarrow \text{Ni}(s) + \text{MgSO}_4(aq)\). For reaction (b), write the unbalanced equation as \(\text{Al}(s) + \text{SnSO}_4(aq) \rightarrow \text{Sn}(s) + \text{Al}_2(SO_4)_3(aq)\).

Balance the Equations

For (a): The equation \(\text{Mg}(s) + \text{NiSO}_4(aq) \rightarrow \text{Ni}(s) + \text{MgSO}_4(aq)\) is already balanced as each side has 1 Mg, 1 Ni, 1 S, and 4 O atoms. For (b): To balance Al and SO₄, write 2 \(\text{Al}(s) + 3 \text{SnSO}_4(aq) \rightarrow 3 \text{Sn}(s) + \text{Al}_2(SO_4)_3(aq)\), balancing charges and atoms: 2 Al, 3 Sn, 3 SO₄ on each side.

Key concepts

Activity Series of Metals

The activity series of metals is a crucial concept for understanding single-replacement reactions. It is essentially a list that ranks metals based on their reactivity. Metals placed higher on the list can replace metals that are lower in single-replacement reactions. Such a sequence aids in predicting whether a chemical reaction will occur.

Consider reaction (a) involving magnesium and nickel sulfate. When we refer to the activity series, we find magnesium positioned above nickel, indicating its higher reactivity. This suggests that magnesium can successfully replace nickel in nickel sulfate, resulting in a new compound, magnesium sulfate, and leaving nickel in its elemental form.

The activity series helps to efficiently determine outcomes in reactions, and it's a practical tool for anyone learning about chemical reactivity. A typical activity series may include:

• Potassium (K) - Highly reactive
• Sodium (Na)
• Magnesium (Mg)
• Aluminum (Al)
• Nickel (Ni)
• Lead (Pb) - Less reactive

This order allows chemists and students to predict the feasibility of reactions, making it easier to understand and memorize chemical behaviors.

Balancing Chemical Equations

Balancing chemical equations is an essential skill in chemistry that ensures the conservation of mass and follows the law of conservation of matter. This means that the number of each type of atom on the reactant side must be equal to the number on the product side.

The process begins by writing the unbalanced equation after predicting the reaction using the activity series. For instance, in reaction (a): \(\text{Mg}(s) + \text{NiSO}_4(aq) \rightarrow \text{Ni}(s) + \text{MgSO}_4(aq)\). To confirm its balance, check that one atom of Mg and Ni, along with equal amounts of sulfate, exist on both sides.

However, reaction (b): \(\text{Al}(s) + \text{SnSO}_4(aq) \rightarrow \text{Sn}(s) + \text{Al}_2(SO_4)_3(aq)\) is initially not balanced. It requires adjusting coefficients to achieve balance:

• Balance aluminum by placing a coefficient of 2 before it: \(2\text{Al}(s)\)
• Balance tin and sulfate by writing: \(3\text{SnSO}_4(aq)\)
• This gives: \(2\text{Al}(s) + 3\text{SnSO}_4(aq) \rightarrow 3\text{Sn}(s) + \text{Al}_2(SO_4)_3(aq)\)

This method ensures both mass and charge are conserved, adhering to nature's laws.

Reactivity of Metals

The concept of metal reactivity is foundational in chemistry, especially when dealing with single-replacement reactions. Reactivity itself is an indicator of how easily a metal can lose electrons to form positive ions. Highly reactive metals, like potassium and sodium, readily participate in reactions and get oxidized easily.

In our practice scenarios: magnesium (in reaction a) and aluminum (in reaction b) are more reactive than their counterparts, nickel and tin. This allows them to displace the latter from their compounds. Such reactivity patterns are determined by several factors:

• Atomic structure - Elements with fewer electron shells exert stronger attractions.
• Electronegativity - Metals with lower electronegativity lose electrons rapidly.
• Ionization energy - Metals requiring less energy to lose electrons show higher reactivity.

Understanding these factors helps students predict outcomes in chemical reactions and explains why certain reactions occur the way they do. Reactivity trends are predictable based on the position of metals in the periodic table, thus serving as an invaluable tool in chemistry education and applications.