Problem 100 - General Chemistry

Question

Decide whether a reaction occurs for each of the following. If it does not, write \(N R\) after the arrow. If it does, write the balanced molecular equation; then write the net ionic equation. a. \(\mathrm{Al}(\mathrm{OH})_{3}+\mathrm{HNO}_{3} \longrightarrow\) b. \(\mathrm{NaBr}+\mathrm{HClO}_{4} \longrightarrow\) c. \(\mathrm{CaCl}_{2}+\mathrm{NaNO}_{3} \longrightarrow\) d. \(\mathrm{MgSO}_{4}+\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2} \longrightarrow\)

Step-by-Step Solution

Answer

Reactions occur for a and d; b and c are no reaction.

Step 1: Determine Reactivity

For each reaction, analyze if a reaction occurs based on the nature of the reactants. Consider solubility, acid-base neutralization, or redox activity. Reactions occur between reactive species to form products that are typically more stable than the reactants.

Step 2: Reaction Analysis - Part a

The reaction between \(\mathrm{Al}(\mathrm{OH})_{3}+\mathrm{HNO}_{3}\) is possible due to acid-base neutralization. Aluminum hydroxide, \(\mathrm{Al}(\mathrm{OH})_{3}\), a base, reacts with nitric acid, \(\mathrm{HNO}_{3}\), an acid, to form aluminum nitrate, \(\mathrm{Al}(\mathrm{NO}_{3})_{3}\), and water. The balanced molecular equation is: \[ \mathrm{Al}(\mathrm{OH})_{3} + 3 \mathrm{HNO}_{3} \rightarrow \mathrm{Al}(\mathrm{NO}_{3})_{3} + 3\mathrm{H}_{2}\mathrm{O} \]. The net ionic equation is: \[ \mathrm{Al}(\mathrm{OH})_{3} + 3\mathrm{H}^{+} \rightarrow \mathrm{Al}^{3+} + 3\mathrm{H}_{2}\mathrm{O} \].

Step 3: Reaction Analysis - Part b

The reaction between \(\mathrm{NaBr}+\mathrm{HClO}_{4}\) involves a strong acid, perchloric acid \(\mathrm{HClO}_{4}\), and a salt \(\mathrm{NaBr}\). However, no driving force such as precipitate formation, gas evolution, or weak electrolyte is present as all products remain ions in solution. The equation is: \[ \mathrm{NaBr} + \mathrm{HClO}_{4} \rightarrow \mathrm{Na}^+ + \mathrm{ClO}_{4}^- + \mathrm{HBr} \]. However, as no significant change occurs, write `NR` for 'No Reaction'.

Step 4: Reaction Analysis - Part c

The reaction \(\mathrm{CaCl}_{2} + \mathrm{NaNO}_{3}\) involves two soluble salts, calcium chloride and sodium nitrate. Upon mixing, no precipitate, gas, or unsustainable ion forms. All ions remain in solution. Thus, write `NR` for 'No Reaction'.

Step 5: Reaction Analysis - Part d

Mixing \(\mathrm{MgSO}_{4}\) and \(\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}\) offers a reaction potential as barium sulfate \(\mathrm{BaSO}_{4}\) is an insoluble precipitate. The balanced molecular equation is: \[ \mathrm{MgSO}_{4} + \mathrm{Ba}(\mathrm{NO}_{3})_{2} \rightarrow \mathrm{BaSO}_{4} \downarrow + \mathrm{Mg}(\mathrm{NO}_{3})_{2} \]. The net ionic equation involves only species that change state: \[ \mathrm{Ba}^{2+} + \mathrm{SO}_{4}^{2-} \rightarrow \mathrm{BaSO}_{4} \downarrow \].

Key Concepts

Acid-Base Reactions

Acid-base reactions are fundamental chemical processes that occur when an acid and a base react to form water and a salt. This is a type of double displacement reaction and is often referred to as neutralization. In the context of the exercise, the reaction between aluminum hydroxide, a base, and nitric acid, an acid, results in the formation of aluminum nitrate and water.
The balanced molecular equation is shown as:

• \( \mathrm{Al}(\mathrm{OH})_{3} + 3 \mathrm{HNO}_{3} \rightarrow \mathrm{Al}(\mathrm{NO}_{3})_{3} + 3\mathrm{H}_{2}\mathrm{O} \)

The net ionic equation focuses on the ions that participate directly in the reaction:

• \( \mathrm{Al}(\mathrm{OH})_{3} + 3\mathrm{H}^{+} \rightarrow \mathrm{Al}^{3+} + 3\mathrm{H}_{2}\mathrm{O} \)

This results from the direct interaction of \( \mathrm{H}^{+} \) ions from the acid and the aluminum hydroxide, which forms aluminum ions and water in the solution.

Precipitation Reactions

Precipitation reactions occur when two soluble ionic compounds in aqueous solution react to form an insoluble solid known as a precipitate. These reactions are driven by the formation of a solid substance from the solution. An example from the exercise is the reaction between magnesium sulfate and barium nitrate, where barium sulfate is formed as an insoluble precipitate.

• The balanced molecular equation is: \( \mathrm{MgSO}_{4} + \mathrm{Ba}(\mathrm{NO}_{3})_{2} \rightarrow \mathrm{BaSO}_{4} \, \downarrow + \mathrm{Mg}(\mathrm{NO}_{3})_{2} \)
• The net ionic equation focuses only on the species that form the precipitate: \( \mathrm{Ba}^{2+} + \mathrm{SO}_{4}^{2-} \rightarrow \mathrm{BaSO}_{4} \, \downarrow \)

In this net ionic equation, only the barium and sulfate ions are involved, illustrating the simplicity and usefulness of net ionic equations to show the actual chemical change.

Net Ionic Equations

Net ionic equations are a simplified form of chemical equations that show only the ions and molecules directly involved in the reaction. This form is useful to eliminate spectator ions, which do not participate in the chemical change. For instance, when considering the acid-base reaction given in the exercise, the net ionic equation retains only the \( \mathrm{H}^{+} \) and \( \mathrm{Al}(\mathrm{OH})_{3} \) reactant ions, and the resulting products \( \mathrm{Al}^{3+} \) and \( \mathrm{H}_{2}\mathrm{O} \).To write a net ionic equation:

• First, start with the balanced molecular equation.
• Separate all aqueous substances into their constituent ions.
• Eliminate any spectator ions, which appear unchanged on both sides of the equation.

By focusing only on the ions that change their state, net ionic equations provide a clearer view of the actual chemical transformations taking place.

Molecular Equations

Molecular equations provide a complete overview of the reactants and products involved in a chemical reaction as intact molecules instead of their ionic forms. They are balanced to ensure that matter is conserved and can be crucial for understanding all substances involved in the reactions.For example, in the assessment of the magnesium sulfate and barium nitrate reaction, the molecular equation is:

• \( \mathrm{MgSO}_{4} + \mathrm{Ba}(\mathrm{NO}_{3})_{2} \rightarrow \mathrm{BaSO}_{4} \, \downarrow + \mathrm{Mg}(\mathrm{NO}_{3})_{2} \)

This equation reflects the stoichiometry of the reaction, showing full compounds rather than ions. Therefore, these equations help to ensure all mass and charge are balanced in chemical equations, providing the framework from which information about the reaction can be derived more easily, such as constituent ions or whether a reaction forms a precipitate or not.