Problem 46 - Chemistry and Chemical Reactivity

Question

Balance each of the following equations, and then write the net ionic equation. Show states for all reactants and products (s, \(\ell, \mathrm{g},\) aq). (a) the reaction of sodium hydroxide and iron(II) chloride to give iron(II) hydroxide and sodium chloride (b) the reaction of barium chloride with sodium carbonate to give barium carbonate and sodium chloride (c) the reaction of ammonia with phosphoric acid

Step-by-Step Solution

Answer

(a) Fe²⁺(aq) + 2OH⁻(aq) → Fe(OH)₂(s); (b) Ba²⁺(aq) + CO₃²⁻(aq) → BaCO₃(s); (c) 3NH₃(aq) + 3H⁺(aq) → 3NH₄⁺(aq).

Step 1: Write the Unbalanced Chemical Equation for Reaction (a)

The reactants are sodium hydroxide (NaOH) and iron(II) chloride (FeClext{2}). The products are iron(II) hydroxide (Fe(OH)ext{2}) and sodium chloride (NaCl). We start by writing the unbalanced equation:$$\text{NaOH (aq)} + \text{FeCl}_2 \text{(aq)} \rightarrow \text{Fe(OH)}_2 \text{(s)} + \text{NaCl (aq)}$$.

Step 2: Balance the Chemical Equation for Reaction (a)

Balance the equation by ensuring the same number of each type of atom appears on both sides. For this reaction, two sodiums, two hydroxides, and two chlorides are needed. The balanced equation is:$$2\; \text{NaOH (aq)} + \text{FeCl}_2 \text{(aq)} \rightarrow \text{Fe(OH)}_2 \text{(s)} + 2\; \text{NaCl (aq)}$$.

Step 3: Determine the Net Ionic Equation for Reaction (a)

Write the total ionic equation and cancel out the spectator ions (Nae^{+} and Cle^{-}):The total ionic equation is:$$2\;\text{Na}^{+}\text{(aq)} + 2\;\text{OH}^{-}\text{(aq)} + \text{Fe}^{2+}\text{(aq)} + 2\;\text{Cl}^{-}\text{(aq)} \rightarrow \text{Fe(OH)}_2\text{(s)} + 2\;\text{Na}^{+}\text{(aq)} + 2\;\text{Cl}^{-}\text{(aq)}.$$The net ionic equation is:$$\text{Fe}^{2+}\text{(aq)} + 2\;\text{OH}^{-}\text{(aq)} \rightarrow \text{Fe(OH)}_2 \text{(s)}.$$.

Step 4: Write the Unbalanced Chemical Equation for Reaction (b)

The reactants are barium chloride (BaCle_{2}) and sodium carbonate (Nae_2COe_{3}). The products are barium carbonate (BaCOe_3) and sodium chloride (NaCl). The unbalanced equation is:$$\text{BaCl}_2 (\text{aq}) + \text{Na}_2\text{CO}_3 (\text{aq}) \rightarrow \text{BaCO}_3 (\text{s}) + \text{NaCl} (\text{aq})$$.

Step 5: Balance the Chemical Equation for Reaction (b)

Ensure the number of each type of atom on both sides is the same. The balanced equation is:$$\text{BaCl}_2 (\text{aq}) + \text{Na}_2\text{CO}_3 (\text{aq}) \rightarrow \text{BaCO}_3 (\text{s}) + 2\; \text{NaCl} (\text{aq})$$.

Step 6: Determine the Net Ionic Equation for Reaction (b)

Write the total ionic equation and cancel the spectator ions (Nae^{+} and Cle^{-}):The total ionic equation is:$$\text{Ba}^{2+}\text{(aq)} + 2\;\text{Cl}^{-}\text{(aq)} + 2\;\text{Na}^{+}\text{(aq)} + \text{CO}_3^{2-}\text{(aq)} \rightarrow \text{BaCO}_3\text{(s)} + 2\;\text{Na}^{+}\text{(aq)} + 2\;\text{Cl}^{-}\text{(aq)}$$.The net ionic equation is:$$\text{Ba}^{2+}\text{(aq)} + \text{CO}_3^{2-}\text{(aq)} \rightarrow \text{BaCO}_3 \text{(s)}.$$.

Step 7: Write the Unbalanced Chemical Equation for Reaction (c)

The reactants are ammonia (NH₃) and phosphoric acid (H₃PO₄). The product will include ammonium phosphate ((NH₄)₃PO₄):$$\text{NH}_3(\text{aq}) + \text{H}_3\text{PO}_4(\text{aq}) \rightarrow \text{(NH}_4)_3\text{PO}_4 (\text{aq})$$. Note that ammonia will react with each hydrogen in phosphoric acid.

Step 8: Balance the Chemical Equation for Reaction (c)

For balancing this equation, we need 3 ammonia molecules for each phosphoric acid to form 1 molecule of ammonium phosphate:$$3\; \text{NH}_3(\text{aq}) + \text{H}_3\text{PO}_4(\text{aq}) \rightarrow \text{(NH}_4)_3\text{PO}_4(\text{aq})$$.

Step 9: Determine the Net Ionic Equation for Reaction (c)

Ammonia reacts with the hydrogen ions from phosphoric acid to form ammonium ions. The net ionic equation considering dissolution in solution is:$$3\; \text{NH}_3(\text{aq}) + 3\; \text{H}^+(\text{aq}) \rightarrow 3\; \text{NH}_4^+(\text{aq}).$$

Key Concepts

Net Ionic Equations

Net ionic equations simplify chemical reactions by only showing the species that actively participate in the reaction. This method hones in on the essence of the chemical change, removing all the ions that don't alter during the reaction. These are called spectator ions.
For a net ionic equation, start by writing the full ionic equation, which reveals all the ions present in the solution. Then, identify and eliminate the spectator ions.

• Example: In the reaction between sodium hydroxide (\( \text{NaOH} \)) and iron(II) chloride (\( \text{FeCl}_2 \)), the net ionic equation is only concerned with the formation of iron(II) hydroxide (\( \text{Fe(OH)}_2 \)). The sodium (\( \text{Na}^+ \)) and chloride ions (\( \text{Cl}^- \)) don't change and are thus spectator ions. The net ionic equation simplifies to: \[ \text{Fe}^{2+}(\text{aq}) + 2\, \text{OH}^-(\text{aq}) \rightarrow \text{Fe(OH)}_2(\text{s}) \]

This approach is a crucial skill because it highlights the essential action in chemical equations, focusing on the key transformation in reactions.

Chemical Reactants and Products

In a chemical reaction, reactants are the starting substances, and products are the substances formed by the reaction. Understanding the reactants and products is key to predicting what happens in a chemical process.
Chemical Reactants:

• The starting materials in a chemical reaction.
• For example, the reactants in the reaction between barium chloride (\( \text{BaCl}_2 \)) and sodium carbonate (\( \text{Na}_2\text{CO}_3 \)) are the ions that form in solution: \( \text{Ba}^{2+}, \text{Cl}^-, \text{Na}^+, \text{CO}_3^{2-} \).

Chemical Products:

• The new substances produced by the reaction.
• In the aforementioned barium reaction, the products are barium carbonate (\( \text{BaCO}_3 \), a solid precipitate) and aqueous sodium chloride (\( \text{NaCl} \)).

Knowing reactants and products allows chemists to balance equations and predict reaction outcomes.

Precipitation Reactions

Precipitation reactions occur when two aqueous solutions mix to form a solid, known as a precipitate. These reactions are an essential type of chemical reaction that transforms dissolved substances into an insoluble product.
To predict and understand them, consider the solubility rules, which help determine if a compound will remain dissolved.
Key Points about Precipitation Reactions:

• Occurs when ions in solution form an insoluble product.
• In the example of the reaction between barium chloride (\( \text{BaCl}_2 \)) and sodium carbonate (\( \text{Na}_2\text{CO}_3 \)), barium carbonate (\( \text{BaCO}_3 \)) is the precipitate.
• Recognizable by the formation of a solid in a previously clear solution.

This type of reaction is invaluable in analytical chemistry for identifying the presence of particular ions in a solution.