Question

Write balanced molecular and net ionic equations for the following reactions in aqueous solution. (a) copper \(+\) silver aitrate copper(II) nitrale \(+\) silver (b) iron(1I) axide + hydrochloric aciul iron(II) chloride \(+\) water

Short answer

Balanced molecular and net ionic equations: (a) balanced molecular equation: Cu + 2AgNO3 -> Cu(NO3)2 + 2Ag, net ionic equation: Cu + 2Ag^+ -> Cu^{2+} + 2Ag. (b) balanced molecular equation: FeO + 2HCl -> FeCl2 + H2O, net ionic equation: Fe^{2+} + 2Cl^- -> Fe^{2+} + 2Cl^-.

Step-by-step solution

Write down the unbalanced equations (for both a and b)

For (a) the unbalanced equation is: \[ Cu + AgNO_3 \rightarrow Cu(NO_3)_2 + Ag \] For (b) the unbalanced equation is: \[ FeO + HCl \rightarrow FeCl_2 + H_2O \]

Balance the molecular reactions (for both a and b)

For (a) it is clear that there are 2 nitrate ions on the right side of the equation but only one on the left side. Therefore balance the equation by writing it as: \[ Cu + 2AgNO_3 \rightarrow Cu(NO_3)_2 + 2Ag \] This equation now has 2 Ag atoms, 1 Cu atom and 2 NO3 groups on both sides of the equation. For (b), add a 2 in front of HCl and H2O to balance the equation: \[ FeO + 2HCl \rightarrow FeCl_2 + H_2O \] This balanced equation has 1 Fe atom, 1 O atom, 2 H atoms and 2 Cl atoms on both sides of the equation.

Distinguish between ionic and molecular species (for both a and b)

For (a) the compounds that exist as ions in solution (since this is an aqueous reaction) are AgNO3 and Cu(NO3)2. For (b), the compounds that exist as ions are FeO, HCl and FeCl2.

Write down the net ionic equations (for both a and b)

For (a) the net ionic equation will be: \[ Cu + 2Ag^+ \rightarrow Cu^{2+} + 2Ag \] For (b) the net ionic equation will be: \[ Fe^{2+} + 2Cl^- \rightarrow Fe^{2+} + 2Cl^- \]

Key concepts

Molecular Equations

When representing chemical reactions, we often start with writing the molecular equations. These equations show all the reactants and products as compounds, using their complete chemical formulas. For example, in reaction (a), the reaction between copper and silver nitrate in water is given as:
\[ Cu + 2AgNO_3 \rightarrow Cu(NO_3)_2 + 2Ag \]
In this format, each compound is fully written out, including their molecular forms. This comprehensive display makes it clear to visualize what substances are reacting and what substances are being formed.
Moving on to reaction (b), iron(II) oxide reacts with hydrochloric acid:
\[ FeO + 2HCl \rightarrow FeCl_2 + H_2O \]
The molecular equation lays the groundwork for understanding the process, depicting clearly the transformations happening in a chemical reaction. Despite being informative, molecular equations can sometimes mask the ionic processes in solution. That’s where net ionic equations come into play.

Net Ionic Equations

Net ionic equations are a refined representation that strip down the reaction to its essential elements. They focus solely on the species that undergo a chemical change, often ignoring spectator ions that do not participate directly in the reaction.
For reaction (a) involving copper and silver nitrate, the net ionic equation specifically highlights the transformation of ions:
\[ Cu + 2Ag^+ \rightarrow Cu^{2+} + 2Ag \]
In this equation, only the copper metal and silver ions are shown, as these are the entities actively changing during the reaction. The nitrate ions are not included since they do not participate in the reaction directly.
In contrast, reaction (b) with iron(II) oxide and hydrochloric acid appears different when looking at net ionic terms. Although the original step in the solution showed all ions involved, the correct net ionic equation for the interaction should depict the formation of complex reactants and the resulting products without unnecessary ions. This understanding requires careful observation and understanding of ion behavior in aqueous solutions.
Net ionic equations help students focus on the actual changes happening, making them a powerful tool for mastering chemical reactions by simplifying them to their core components.

Balancing Equations

Balancing chemical equations is a fundamental skill in chemistry, vital for obeying the Law of Conservation of Mass. This law states that matter cannot be created or destroyed in a chemical reaction. Hence, the number of atoms for each element should remain constant throughout a reaction.
To balance an equation like in reaction (a), \[ Cu + 2AgNO_3 \rightarrow Cu(NO_3)_2 + 2Ag \] we ensure the same number of copper, silver, and nitrate molecules on both sides of the equation. Here, adding coefficients balances each element to accurately reflect the quantities reacting and produced.
Similarly, for reaction (b), the balancing of \[ FeO + 2HCl \rightarrow FeCl_2 + H_2O \]
requires placing a coefficient of 2 before HCl and before the water product to ensure hydrogen and chlorine atoms are equal on both sides.

• Examine each element or polyatomic ion separately.
• Adjust coefficients (not subscripts) to get the same number of each atom on both sides.
• Recheck your work to confirm the balance.

Balancing ensures both mass and charge conservation, which are crucial for the validity of the chemical reaction equations. It’s not only a mechanical process but also a logical assessment of the reaction as a whole.