Problem 95 - Chemistry: The Central Science

Question

Antacids are often used to relieve pain and promote healing in the treatment of mild ulcers. Write balanced net ionic equations for the reactions between the \(\mathrm{HCl}(a q)\) in the stomach and each of the following substances used in various antacids: (a) \(\mathrm{Al}(\mathrm{OH})_{3}(\mathrm{~s})\), (b) \(\mathrm{Mg}(\mathrm{OH})_{2}(\mathrm{~s})\), (c) \(\mathrm{MgCO}_{3}(s)\) (d) \(\mathrm{NaAl}\left(\mathrm{CO}_{3}\right)(\mathrm{OH})_{2}(s)\), (e) \(\mathrm{CaCO}_{3}(s)\)

Step-by-Step Solution

Answer

The balanced net ionic equations for the reactions between HCl and the given antacid substances are: (a) \(\mathrm{Al(OH)_3(s) + 3H^+(aq) \rightarrow Al^{3+}(aq) + 3H_2O(l)}\) (b) \(\mathrm{Mg(OH)_2(s) + 2H^+(aq) \rightarrow Mg^{2+}(aq) + 2H_2O(l)}\) (c) \(\mathrm{MgCO_3(s) + 2H^+(aq) \rightarrow Mg^{2+}(aq) + H_2O(l) + CO_2(g)}\) (d) \(\mathrm{NaAl(CO3)(OH)_2(s) + 6H^+(aq) \rightarrow Al^{3+}(aq) + 3H_2O(l) + 2CO_2(g)}\) (e) \(\mathrm{CaCO_3(s) + 2H^+(aq) \rightarrow Ca^{2+}(aq) + H_2O(l) + CO_2(g)}\)

Step 1: Write the balanced chemical equation

The balanced equation for the reaction between \(\mathrm{HCl}\) and \(\mathrm{Al}(\mathrm{OH})_{3}\) is: $$\mathrm{Al(OH)_3(s) + 3HCl(aq) \rightarrow AlCl_3(aq) + 3H_2O(l)}$$

Step 2: Write the total ionic equation

In the total ionic equation, we break the soluble compounds into their constituent ions: $$\mathrm{Al(OH)_3(s) + 3H^+(aq) + 3Cl^-(aq) \rightarrow Al^{3+}(aq) + 3Cl^-(aq) + 3H_2O(l)}$$

Step 3: Find the net ionic equation

Removing the spectator ions (the ions that are unchanged in the reaction) gives the net ionic equation: $$\mathrm{Al(OH)_3(s) + 3H^+(aq) \rightarrow Al^{3+}(aq) + 3H_2O(l)}$$ (b) Reaction with \(\mathrm{Mg(OH)_2(s)}\)

Step 1: Write the balanced chemical equation

The balanced equation for the reaction between \(\mathrm{HCl}\) and \(\mathrm{Mg(OH)_2}\) is: $$\mathrm{Mg(OH)_2(s) + 2HCl(aq) \rightarrow MgCl_2(aq) + 2H_2O(l)}$$

Step 2: Write the total ionic equation

In the total ionic equation, we break the soluble compounds into their constituent ions: $$\mathrm{Mg(OH)_2(s) + 2H^+(aq) + 2Cl^-(aq) \rightarrow Mg^{2+}(aq) + 2Cl^-(aq) + 2H_2O(l)}$$

Step 3: Find the net ionic equation

Removing the spectator ions gives the net ionic equation: $$\mathrm{Mg(OH)_2(s) + 2H^+(aq) \rightarrow Mg^{2+}(aq) + 2H_2O(l)}$$ (c) Reaction with \(\mathrm{MgCO_3(s)}\)

Step 1: Write the balanced chemical equation

The balanced equation for the reaction between \(\mathrm{HCl}\) and \(\mathrm{MgCO_3(s)}\) is: $$\mathrm{MgCO_3(s) + 2HCl(aq) \rightarrow MgCl_2(aq) + H_2O(l) + CO_2(g)}$$

Step 2: Write the total ionic equation

In the total ionic equation, we break the soluble compounds into their constituent ions: $$\mathrm{MgCO_3(s) + 2H^+(aq) + 2Cl^-(aq) \rightarrow Mg^{2+}(aq) + 2Cl^-(aq) + H_2O(l) + CO_2(g)}$$

Step 3: Find the net ionic equation

Removing the spectator ions gives the net ionic equation: $$\mathrm{MgCO_3(s) + 2H^+(aq) \rightarrow Mg^{2+}(aq) + H_2O(l) + CO_2(g)}$$ (d) Reaction with \(\mathrm{NaAl(CO_3)(OH)_2(s)}\)

Step 1: Write the balanced chemical equation

The balanced equation for the reaction between \(\mathrm{HCl}\) and \(\mathrm{NaAl(CO_3)(OH)_2}\) is: $$\mathrm{NaAl(CO3)(OH)_2(s) + 6HCl(aq) \rightarrow AlCl_3(aq) + NaCl(aq) + 3H_2O(l) + 2CO_2(g)}$$

Step 2: Write the total ionic equation

In the total ionic equation, we break the soluble compounds into their constituent ions: $$\mathrm{NaAl(CO3)(OH)_2(s) + 6H^+(aq) + 6Cl^-(aq) \rightarrow Al^{3+}(aq) + 6Cl^-(aq) + 3H_2O(l) + 2CO_2(g)}$$

Step 3: Find the net ionic equation

Removing the spectator ions gives the net ionic equation: $$\mathrm{NaAl(CO3)(OH)_2(s) + 6H^+(aq) \rightarrow Al^{3+}(aq) + 3H_2O(l) + 2CO_2(g)}$$ (e) Reaction with \(\mathrm{CaCO_3(s)}\)

Step 1: Write the balanced chemical equation

The balanced equation for the reaction between \(\mathrm{HCl}\) and \(\mathrm{CaCO_3}\) is: $$\mathrm{CaCO_3(s) + 2HCl(aq) \rightarrow CaCl_2(aq) + H_2O(l) + CO_2(g)}$$

Step 2: Write the total ionic equation

In the total ionic equation, we break the soluble compounds into their constituent ions: $$\mathrm{CaCO_3(s) + 2H^+(aq) + 2Cl^-(aq) \rightarrow Ca^{2+}(aq) + 2Cl^-(aq) + H_2O(l) + CO_2(g)}$$

Step 3: Find the net ionic equation

Removing the spectator ions gives the net ionic equation: $$\mathrm{CaCO_3(s) + 2H^+(aq) \rightarrow Ca^{2+}(aq) + H_2O(l) + CO_2(g)}$$

Key Concepts

Chemical Reactions

Understanding chemical reactions is crucial for students grappling with the complexities of chemistry. A chemical reaction involves the transformation of substances through the breaking of bonds in reactants and the formation of new bonds to create products. In the context of antacids, these reactions typically occur between an acid and a base. Antacids, which contain basic substances, react with hydrochloric acid (HCl) in the stomach to produce salt, water, and sometimes gas.

For instance, when aluminum hydroxide, \(\mathrm{Al(OH)_3}\), reacts with HCl, they produce aluminum chloride and water as products. While the molecular equation provides a straightforward picture, the total ionic and net ionic equations give a deeper insight into the specifics of the reaction, illustrating exactly which ions and compounds participate directly in the reaction process.

Acid-Base Neutralization

Acid-base neutralization is a specific type of chemical reaction where an acid and a base react to form water and a salt. This is particularly interesting in the context of antacids, which are basic substances designed to neutralize stomach acid and alleviate discomfort.

When we look at the reaction between magnesium hydroxide, \(\mathrm{Mg(OH)_2}\), and HCl, the products are magnesium chloride and water, demonstrating a typical neutralization reaction. By understanding these reactions through net ionic equations, students gain insight into the stoichiometry and the actual exchange of ions that lead to the relief from acidity. The careful balancing of these equations reflects the law of conservation of mass, ensuring that the number of atoms for each element is the same on both sides of the reaction.

Solubility Rules

Solubility rules are a set of guidelines used to predict whether an ionic compound will dissolve in water. These rules are essential when writing total and net ionic equations, as they inform us which compounds break down into ions in aqueous solution and which remain intact. These rules help elucidate the reactants and products in a state they would be found in a natural setting, like the stomach.

For example, calcium carbonate, \(\mathrm{CaCO_3}\), does not dissolve in water and is thus written as a solid in the total ionic equation. Solubility rules tell us that most carbonate compounds are insoluble except when paired with alkali metal cations or ammonium, which is why \(\mathrm{CaCO_3}\) reacts with HCl to form a soluble \(\mathrm{Ca}^{2+}\) ion, carbon dioxide, and water. This understanding is not only critical for solving net ionic equations but also helps in predicting the outcomes of reactions and in the design of pharmaceuticals such as antacids.