Problem 54 - Chemistry: An Atoms-Focused Approach

Question

Write a balanced molecular equation and a net ionic equation for the following reactions: a. Solid aluminum hydroxide reacts with a solution of hydrobromic acid. b. A solution of sulfuric acid reacts with solid sodium carbonate. c. A solution of calcium hydroxide reacts with a solution of nitric acid.

Step-by-Step Solution

Answer

Question: Write balanced molecular and net ionic equations for the following reactions: a. Solid aluminum hydroxide reacts with a solution of hydrobromic acid. b. A solution of sulfuric acid reacts with solid sodium carbonate. c. A solution of calcium hydroxide reacts with a solution of nitric acid. Answer: a. Balanced Molecular Equation: Al(OH)3 (s) + 3HBr (aq) → AlBr3 (aq) + 3H2O (l) Net Ionic Equation: Al(OH)3 (s) + 3H+ (aq) → Al3+ (aq) + 3H2O (l) b. Balanced Molecular Equation: H2SO4 (aq) + Na2CO3 (s) → Na2SO4 (aq) + H2O (l) + CO2 (g) Net Ionic Equation: 2H+ (aq) + CO3^2- (s) → H2O (l) + CO2 (g) c. Balanced Molecular Equation: Ca(OH)2 (aq) + 2HNO3 (aq) → Ca(NO3)2 (aq) + 2H2O (l) Net Ionic Equation: 2OH- (aq) + 2H+ (aq) → 2H2O (l)

Step 1: Write the unbalanced molecular equation.

Write the unbalanced molecular equation, indicating the correct reactants and products. Al(OH)3 (s) + HBr (aq) → AlBr3 (aq) + H2O (l)

Step 2: Balance the molecular equation.

Now, we need to balance the molecular equation by ensuring that the number of atoms for each element is equal on both sides of the equation. Al(OH)3 (s) + 3HBr (aq) → AlBr3 (aq) + 3H2O (l)

Step 3: Write the complete ionic equation.

We will then write the complete ionic equation, which shows all of the ions present in the reaction. Al(OH)3 (s) + 3H+ (aq) + 3Br- (aq) → Al3+ (aq) + 3Br- (aq) + 3H2O (l)

Step 4: Write the net ionic equation.

Finally, we can write the net ionic equation by removing the spectator ions and including only the ions that participate in the reaction. Al(OH)3 (s) + 3H+ (aq) → Al3+ (aq) + 3H2O (l) b. A solution of sulfuric acid reacts with solid sodium carbonate.

Step 1: Write the unbalanced molecular equation.

Write the unbalanced molecular equation for the reaction between sulfuric acid and solid sodium carbonate. H2SO4 (aq) + Na2CO3 (s) → Na2SO4 (aq) + H2O (l) + CO2 (g)

Step 2: Balance the molecular equation.

Balance the molecular equation by ensuring the number of atoms for each element is equal on both sides. H2SO4 (aq) + Na2CO3 (s) → Na2SO4 (aq) + H2O (l) + CO2 (g) (No changes needed as the equation is already balanced)

Step 3: Write the complete ionic equation.

Write the complete ionic equation for the reaction. 2H+ (aq) + SO4^2- (aq) + 2Na+ (aq) + CO3^2- (s) → 2Na+ (aq) + SO4^2- (aq) + H2O (l) + CO2 (g)

Step 4: Write the net ionic equation.

Write the net ionic equation, removing the spectator ions. 2H+ (aq) + CO3^2- (s) → H2O (l) + CO2 (g) c. A solution of calcium hydroxide reacts with a solution of nitric acid.

Step 1: Write the unbalanced molecular equation.

Write the unbalanced molecular equation for the reaction between calcium hydroxide and nitric acid. Ca(OH)2 (aq) + HNO3 (aq) → Ca(NO3)2 (aq) + H2O (l)

Step 2: Balance the molecular equation.

Balance the molecular equation ensuring the number of atoms for each element is equal on both sides. Ca(OH)2 (aq) + 2HNO3 (aq) → Ca(NO3)2 (aq) + 2H2O (l)

Step 3: Write the complete ionic equation.

Write the complete ionic equation for the reaction. Ca2+ (aq) + 2OH- (aq) + 2H+ (aq) + 2NO3- (aq) → Ca2+ (aq) + 2NO3- (aq) + 2H2O (l)

Step 4: Write the net ionic equation.

Write the net ionic equation, removing the spectator ions. 2OH- (aq) + 2H+ (aq) → 2H2O (l)

Key Concepts

Balanced Molecular Equation

When we talk about a balanced molecular equation, we're essentially presenting a chemical reaction where all reactants and products are represented by their molecular formulas. The key here is to ensure that the number of atoms for each element is equal on both sides of the equation. This reflects the law of conservation of mass.

Take, for example, the reaction between aluminum hydroxide and hydrobromic acid:

• Unbalanced: Al(OH)_3 (s) + HBr (aq) → AlBr_3 (aq) + H_2O (l)
• Balanced: Al(OH)_3 (s) + 3HBr (aq) → AlBr_3 (aq) + 3H_2O (l)

The balanced equation shows that three molecules of hydrobromic acid are needed to completely react with one molecule of aluminum hydroxide, producing aluminum bromide and water.

Remember, balancing equations is not about changing the compounds themselves, but adjusting the coefficients in front of them. This ensures mass is conserved across the entire reaction.

Net Ionic Equation

A net ionic equation focuses on the ions and molecules directly involved in the reaction. It removes the spectator ions, those that do not participate in the reaction, helping to clearly demonstrate the change occurring. This type of equation is particularly useful in reactions where ions in solution come together to form a precipitate or gas.

For example, consider the reaction between calcium hydroxide and nitric acid:

• Complete Ionic Equation: Ca^{2+} (aq) + 2OH^- (aq) + 2H^+ (aq) + 2NO_3^- (aq) → Ca^{2+} (aq) + 2NO_3^- (aq) + 2H_2O (l)
• Net Ionic Equation: 2OH^- (aq) + 2H^+ (aq) → 2H_2O (l)

Here, the spectator ions Ca^{2+} and NO_3^- are removed, simplifying the equation to show only what is actually happening: hydroxide ions react with hydrogen ions to form water.

This simplification helps in understanding the core interaction in a solution, making it a powerful tool for analyzing ionic reactions.

Ionic Reactions

Ionic reactions occur when ions in aqueous solutions interact, often resulting in the formation of a precipitate, water, or gas. These reactions are fundamental in chemistry, especially in fields like analytical chemistry and biochemistry.

Let's explore a common ionic reaction between sulfuric acid and sodium carbonate:

• Molecular Equation: H_2SO_4 (aq) + Na_2CO_3 (s) → Na_2SO_4 (aq) + H_2O (l) + CO_2 (g)
• Net Ionic Equation: 2H^+ (aq) + CO_3^{2-} (s) → H_2O (l) + CO_2 (g)

What’s interesting here is the carbonate reacting with hydrogen ions to produce water and carbon dioxide gas. The sodium and sulfate ions are not shown in the net ionic equation as they don’t partake directly in the formation of products.

Understanding ionic reactions can offer insights into solubility rules, the formation of complex ions, and acid-base chemistry. It's a foundational concept that helps predict product formation in various chemical processes.