Problem 30 - General Chemistry: Principles and Modern Applications

Question

Some baking powders contain the solids \(\mathrm{NaHCO}_{3}\) and \(\mathrm{NaAl}\left(\mathrm{SO}_{4}\right)_{2} .\) When water is added to this mixture of compounds, \(\mathrm{CO}_{2}(\mathrm{g})\) and \(\mathrm{Al}(\mathrm{OH})_{3}(\mathrm{s})\) are two of the products. Write plausible net ionic equations for the formation of these two products.

Step-by-Step Solution

Answer

The net ionic equations for the formation of \(CO_2(g)\) and \(Al(OH)_3(s)\) when \(NaHCO_3\) and \(NaAl(SO_4)_2\) are dissolved in water are:1. \(HCO_3^- (aqueous) + H_2O (l) \rightarrow OH^- (aqueous) + CO_2 (g)\)2. \(Al^{3+} (aqueous) + 3H_2O (l) \rightarrow Al(OH)_3 (s)\

Step 1: Identify the Reaction of NaHCO3 with Water

When sodium bicarbonate (\(NaHCO_3\)) dissolves in water, it breaks down into its constituent ions, \(Na^+\) and \(HCO_3^-\). This bicarbonate ion reacts with water to form hydroxide ion, \(OH^-\), and carbon dioxide gas, \(CO_2\). This can be written as follows:\(HCO_3^- (aqueous) + H_2O (l) \rightarrow OH^- (aqueous) + CO_2 (g)\)Ensure this equation is balanced.

Step 2: Identify the Reaction of NaAl(SO4)2 with Water

When sodium alum (\(NaAl(SO_4)_2\)) dissolves in water, it dissociates into it's constituent ions: \(Na^+\), \(Al^{3+}\), and \(SO_4^{2-}\). The \(Al^{3+}\) ions react with water to form \(Al(OH)_3\). This reaction can be written as:\(Al^{3+} (aqueous) + 3H_2O (l) \rightarrow Al(OH)_3 (s)\)Ensure this equation is balanced.

Step 3: Construct Net Ionic Equations

Now we can construct the net ionic equations by eliminating the spectator ions. As a reminder, net ionic equations don't include ions that don’t participate in the reaction (spectator ions). In these reactions, the \(Na^+\) ions and \(SO_4^{2-}\) ions in the second reaction are the spectator ions.Net Ionic Equation 1:\(HCO_3^- (aqueous) + H_2O (l) \rightarrow OH^- (aqueous) + CO_2 (g)\)Net Ionic Equation 2:\(Al^{3+} (aqueous) + 3H_2O (l) \rightarrow Al(OH)_3 (s)\)

Key Concepts

Baking Powder Chemistry

Baking powder is a hallmark in the culinary world when it comes to baking fluffy and soft treats like cakes and bread. It is a leavening agent that causes dough to expand by releasing gas. Baking powder typically contains sodium bicarbonate (\(\text{NaHCO}_3\)) and an acid like sodium aluminum sulfate (\(\text{NaAl(SO}_4)_2\)). When water is added, a chemical reaction occurs.

• Sodium bicarbonate (\(\text{NaHCO}_3\)), a basic compound, reacts with the acidic component.
• This reaction results in the production of carbon dioxide gas (\(\text{CO}_2\)), leading to the expansion of the batter or dough.
• The carbon dioxide gas forms bubbles within the dough, making it rise.

These reactions are essential in understanding the physics and chemistry behind baking powder's effectiveness in raising the mixture, and enhancing product volume and texture.

Ionic Reactions

Ionic reactions involve the exchange of ions between two compounds, often leading to the formation of a gas, solid, or other reaction products. For baking powder, the ionic reactions are intriguing.

When sodium bicarbonate dissolves in water, it separates into its ions:

• \(\text{Na}^+\) (sodium ion)
• \(\text{HCO}_3^-\) (bicarbonate ion)

The bicarbonate ion further reacts with water:\[\text{HCO}_3^- (aqueous) + \text{H}_2\text{O} (l) \rightarrow \text{OH}^- (aqueous) + \text{CO}_2 (g)\]This step results in the creation of hydroxide ions and carbon dioxide gas, explaining the bubbles we see in rising dough.

Regarding sodium aluminum sulfate, when it interacts with water:

• \(\text{Na}^+\), \(\text{Al}^{3+}\), and \(\text{SO}_4^{2-}\) ions are produced.

The aluminum ions engage with water forming:\[\text{Al}^{3+} (aqueous) + 3\text{H}_2\text{O} (l) \rightarrow \text{Al(OH)}_3 (s)\]This reaction results in the formation of aluminum hydroxide, a solid precipitate.

Chemical Equilibrium

Chemical equilibrium plays a crucial role in understanding how ionic reactions behave in the context of baking powder chemistry. When these reactions reach equilibrium, the rate of the forward reaction is equal to the rate of the reverse reaction, meaning the amounts of reactants and products remain constant over time.

• The decomposition of sodium bicarbonate to produce carbon dioxide is initially fast, balancing the reactions quickly to give a perfect rise to the baked goods.
• Equilibrium ensures that enough carbon dioxide is provided just before the baking process is complete, aiding in maintaining structure and texture.
• Understanding equilibrium helps bakers to perfect baking conditions to maximize the effectiveness of baking powder.

By optimizing conditions such as temperature and ingredient proportions, bakers can control the extent to which these ionic reactions and equilibrium influence their final product. This resembles a dance between science and art, showing how precise changes can affect the outcome of baking.