Question

Write a balanced equation for each of the following single-replacement reactions: (a) Iron is added to a mercury(II) sulfate solution. (b) Mercury is added to a iron(II) sulfate solution.

Short answer

(a) Fe + HgSO_4 → FeSO_4 + Hg (balanced); (b) No reaction occurs.

Step-by-step solution

Identify the Reactants

For part (a), the reactants are iron (Fe) and mercury(II) sulfate (HgSO_4). For part (b), the reactants are mercury (Hg) and iron(II) sulfate (FeSO_4).

Determine the Products

In single-replacement reactions, a more reactive metal will replace a less reactive metal in a compound. For part (a), iron will replace mercury to form iron(II) sulfate (FeSO_4) and elemental mercury (Hg). For part (b), mercury is less reactive than iron, so no reaction will occur.

Write the Chemical Equations

For part (a), the unbalanced chemical equation is Fe + HgSO_4 → FeSO_4 + Hg. As part (b) has no reaction, we do not write an equation for it.

Balance the Equation

For part (a), the equation is already balanced with equal atoms of Fe, Hg, S, and O on both sides: Fe + HgSO_4 → FeSO_4 + Hg. There is no need to balance part (b) as there is no reaction.

Key concepts

Single-Replacement Reaction

Single-replacement reactions are a type of chemical reaction where one element is substituted for another in a compound. This usually involves metals and often takes place in solutions. In a typical single-replacement reaction, you will see a more reactive element displacing a less reactive element from its compound.

Here's how it works: when iron (Fe) is added to mercury(II) sulfate (HgSO_4), the iron, being more reactive, kicks out the mercury (Hg) from the compound. This leads to the formation of a new compound, iron(II) sulfate (FeSO_4), and releases elemental mercury as a byproduct.

This type of reaction is quite common in redox chemistry and is frequently constructed around the idea of comparing the reactivity of different metals. The reactivity of metals is often documented in a list called the reactivity series, which helps predict which metals can replace others in compounds.

Balancing Equations

Balancing chemical equations is an essential skill in chemistry that ensures the law of conservation of mass is followed. This law states that matter cannot be created or destroyed in a chemical reaction. Thus, every atom of each element must be accounted for on both sides of a chemical equation.

Consider the reaction of iron with mercury(II) sulfate:

• Reactants: Fe + HgSO_4
• Products: FeSO_4 + Hg

In the equation above, we start by identifying the number of each type of atom on the reactant and product sides. The task of balancing is to make sure each side has the same number of each type of atom.

The given equation Fe + HgSO_4 → FeSO_4 + Hg is already balanced. It shows one iron atom, one mercury atom, one sulfur atom, and four oxygen atoms on both sides. Balancing becomes more challenging as the complexity of the reactants and products increases, but the same principles apply.

Reactivity Series

The reactivity series is a helpful tool used in predicting the outcomes of single-replacement reactions. It's essentially a list of elements ordered by their reactivity from highest to lowest, primarily focusing on metals.

In single-replacement reactions, a more reactive metal will displace a less reactive metal from its compound. For example:

• Iron is above mercury in the reactivity series. Therefore, iron can replace mercury in its compounds, as seen with Fe replacing Hg in HgSO_4.
• Mercury, being less reactive, cannot replace iron. Thus, no reaction occurs when mercury is added to iron(II) sulfate (FeSO_4).

Understanding where elements lie in the reactivity series assists chemists in predicting not only whether a reaction will occur but also in the design of synthetic pathways in industrial and laboratory settings. Thus, a solid grasp of the reactivity series is crucial for anyone studying chemistry at an advanced level.