Problem 52 - General Chemistry

Question

The following reactions occur in aqueous solution. Complete and balance the molecular equations using phase labels. Then write the net ionic equations. a. \(\mathrm{BaCO}_{3}+\mathrm{HNO}_{3} \longrightarrow\) b. \(\mathrm{K}_{2} \mathrm{~S}+\mathrm{HCl} \longrightarrow\) c. \(\mathrm{CaSO}_{3}(s)+\mathrm{HI} \longrightarrow\)

Step-by-Step Solution

Answer

Molecular: (a) Ba(NO₃)₂(aq) + H₂O(l) + CO₂(g), (b) H₂S(g) + KCl(aq), (c) CaI₂(aq) + H₂O(l) + SO₂(g). Net Ionic: (a) BaCO₃(s) + 2H⁺ → Ba²⁺ + H₂O + CO₂, (b) S²⁻ + 2H⁺ → H₂S, (c) CaSO₃(s) + 2H⁺ → Ca²⁺ + H₂O + SO₂.

Step 1: Write the molecular equations

Identify the reactants and products for each reaction, while considering the possible products of double displacement reactions.- (a) Barium carbonate reacts with nitric acid to produce barium nitrate, water, and carbon dioxide: \[ \mathrm{BaCO}_{3}(s) + 2 \mathrm{HNO}_{3}(aq) \rightarrow \mathrm{Ba(NO}_{3})_{2}(aq) + \mathrm{H}_{2}\mathrm{O}(l) + \mathrm{CO}_{2}(g) \]- (b) Potassium sulfide reacts with hydrochloric acid to produce hydrogen sulfide and potassium chloride: \[ \mathrm{K}_{2} \mathrm{S}(aq) + 2 \mathrm{HCl}(aq) \rightarrow \mathrm{H}_{2}\mathrm{S}(g) + 2\mathrm{KCl}(aq) \]- (c) Calcium sulfite reacts with hydroiodic acid to produce calcium iodide, water, and sulfur dioxide: \[ \mathrm{CaSO}_{3}(s) + 2\mathrm{HI}(aq) \rightarrow \mathrm{CaI}_{2}(aq) + \mathrm{H}_{2}\mathrm{O}(l) + \mathrm{SO}_{2}(g) \]

Step 2: Balance the molecular equations

Ensure each atom's count is the same on both sides of each reaction. The equations from Step 1 are already balanced with respect to the number of atoms for each element involved in the reactions:

Step 3: Write the full ionic equations

Break all the soluble compounds into ions. Solids, gases, and liquids remain unchanged in their molecular forms.- (a) \[ \mathrm{BaCO}_{3}(s) + 2 \mathrm{H^{+}}(aq) + 2 \mathrm{NO}_{3}^{-}(aq) \rightarrow \mathrm{Ba^{2+}}(aq) + 2\mathrm{NO}_{3}^{-}(aq) + \mathrm{H}_{2}\mathrm{O}(l) + \mathrm{CO}_{2}(g) \]- (b) \[ 2\mathrm{K^{+}}(aq) + \mathrm{S^{2-}}(aq) + 2 \mathrm{H^{+}}(aq) + 2 \mathrm{Cl^{-}}(aq) \rightarrow \mathrm{H}_{2}\mathrm{S}(g) + 2\mathrm{K^{+}}(aq) + 2\mathrm{Cl^{-}}(aq) \]- (c) \[ \mathrm{CaSO}_{3}(s) + 2 \mathrm{H^{+}}(aq) + 2\mathrm{I^{-}}(aq) \rightarrow \mathrm{Ca^{2+}}(aq) + 2\mathrm{I^{-}}(aq) + \mathrm{H}_{2}\mathrm{O}(l) + \mathrm{SO}_{2}(g) \]

Step 4: Identify and cancel spectator ions

Spectator ions appear on both sides of the full ionic equations without undergoing any change.- (a) Spectator ions: \( \mathrm{NO}_{3}^{-} \)- (b) Spectator ions: \( \mathrm{K^{+}} \), \( \mathrm{Cl^{-}} \)- (c) Spectator ions: \( \mathrm{I^{-}} \)

Step 5: Write the net ionic equations

Remove the spectator ions from the full ionic equations to yield the net ionic equations.- (a) \[ \mathrm{BaCO}_{3}(s) + 2 \mathrm{H^{+}}(aq) \rightarrow \mathrm{Ba^{2+}}(aq) + \mathrm{H}_{2}\mathrm{O}(l) + \mathrm{CO}_{2}(g) \]- (b) \[ \mathrm{S^{2-}}(aq) + 2 \mathrm{H^{+}}(aq) \rightarrow \mathrm{H}_{2}\mathrm{S}(g) \]- (c) \[ \mathrm{CaSO}_{3}(s) + 2 \mathrm{H^{+}}(aq) \rightarrow \mathrm{Ca^{2+}}(aq) + \mathrm{H}_{2}\mathrm{O}(l) + \mathrm{SO}_{2}(g) \]

Key Concepts

Molecular Equations

Molecular equations offer a complete look at the reactants and products taking part in a chemical reaction. These formulas present substances using their chemical formulas, showing how compounds transform during the reaction. Importantly, the molecular equation does not break down compounds into ions but keeps them whole.

• In the reaction between barium carbonate and nitric acid, the molecular equation is: \[ \mathrm{BaCO}_{3}(s) + 2 \mathrm{HNO}_{3}(aq) \rightarrow \mathrm{Ba(NO}_{3})_{2}(aq) + \mathrm{H}_{2}\mathrm{O}(l) + \mathrm{CO}_{2}(g) \]


• These equations serve as a crucial starting point in identifying participants of the reaction. This helps predict the possible outcomes of chemical interactions.

Understanding molecular equations helps you see the big picture of how different substances interact during a chemical reaction.

Balancing Chemical Equations

Balancing chemical equations ensures that the number of atoms for each element is the same on both sides of the equation. This is a vital step because it adheres to the Law of Conservation of Mass, which states that mass cannot be created or destroyed in a chemical reaction.

• In balancing reactions, coefficients are adjusted to assure each kind of atom appears equally on both sides.


• For instance, in the equation for barium carbonate reacting with nitric acid, notice that there are two molecules of \( \mathrm{HNO}_{3} \) balancing hydrogen and nitrate ions in the reaction: \[ \mathrm{BaCO}_{3}(s) + 2 \mathrm{HNO}_{3}(aq) \rightarrow \mathrm{Ba(NO}_{3})_{2}(aq) + \mathrm{H}_{2}\mathrm{O}(l) + \mathrm{CO}_{2}(g) \]

Proper balance ensures the reactants fully transform into products, providing accurate predictions in experimental settings.

Spectator Ions

Spectator ions are those ions present in a chemical reaction that don’t get involved in the chemical change. While they appear in the full ionic equation, they are unchanged. This makes them non-participants in the true chemical change occurring.

• Spectator ions are useful to identify because they help simplify ionic equations to net ionic equations, showing just the reactive species.


• For example, in the reaction where \( \mathrm{K}_{2} \mathrm{S} \) reacts with \( \mathrm{HCl} \), \( \mathrm{K^{+}} \) and \( \mathrm{Cl^{-}} \) serve as spectator ions. They appear in the same form on both sides of the full ionic equation.

By focusing solely on changes, spectator ions provide a clearer understanding of the core chemical transformations within reactions.

Double Displacement Reactions

Double displacement reactions, also known as metathesis reactions, involve the exchange of ions between two compounds to form two new compounds. This exchange often results in the formation of a precipitate, water, or gas, driving the reaction to completion.

• Common in aqueous solutions, these reactions have the general formula: \( AB + CD \rightarrow AD + CB \).


• In our example, barium carbonate reacting with nitric acid is a double displacement process, leading to products like barium nitrate and carbon dioxide gas.


• Recognizing this type of reaction helps in predicting the products and understanding the driving forces behind chemical processes.

By grasping the fundamentals of double displacement reactions, you improve your skill in anticipating outcomes of chemical interactions, an invaluable tool in chemistry exploration.