Problem 95 - Chemistry The Central Science In Si Units

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 aqueous HCl in the stomach and each of the following substances used in various antacids: \((\mathbf{a}) \mathrm{Al}(\mathrm{OH})_{3}(s),(\mathbf{b}) \mathrm{Mg}(\mathrm{OH})_{2}(s),(\mathbf{c}) \mathrm{MgCO}_{3}(s),\) (d) \(\mathrm{NaAl}\left(\mathrm{CO}_{3}\right)(\mathrm{OH})_{2}(s)\) (e) \(\mathrm{CaCO}_{3}(s)\)

Step-by-Step Solution

Answer

Net ionic equations: (a) \( \mathrm{Al(OH)_3} + 3 \mathrm{H}^{+} \rightarrow \mathrm{Al}^{3+} + 3 \mathrm{H_2O} \), (b) \( \mathrm{Mg(OH)_2} + 2 \mathrm{H}^{+} \rightarrow \mathrm{Mg}^{2+} + 2 \mathrm{H_2O} \), (c) \( \mathrm{MgCO_3} + 2 \mathrm{H}^{+} \rightarrow \mathrm{Mg}^{2+} + \mathrm{CO_2} + \mathrm{H_2O} \), (d) \( \mathrm{NaAl(CO_3)(OH)_2} + 4 \mathrm{H}^{+} \rightarrow \mathrm{Na}^{+} + \mathrm{Al}^{3+} + \mathrm{CO_2} + 3 \mathrm{H_2O} \), (e) \( \mathrm{CaCO_3} + 2 \mathrm{H}^{+} \rightarrow \mathrm{Ca}^{2+} + \mathrm{CO_2} + \mathrm{H_2O} \).

Step 1: Understand the Problem

We need to write balanced net ionic equations for the reactions between stomach hydrochloric acid, HCl(aq), and different antacid substances, each provided in solid form. Net ionic equations focus on the ions involved in the reaction and exclude the spectator ions.

Step 2: Dissolve HCl in Water

In aqueous solution, HCl dissociates completely into its ions: \[ \mathrm{HCl(aq)} \rightarrow \mathrm{H}^{+}(aq) + \mathrm{Cl}^{-}(aq) \] This dissociation applies to all reactions in the stomach involving HCl.

Step 3: Reaction with Aluminum Hydroxide

Aluminum hydroxide, \( \mathrm{Al(OH)_3(s)} \), reacts with HCl(aq). The primary reaction is: \[ \mathrm{Al(OH)_3(s)} + 3 \mathrm{H}^{+}(aq) \rightarrow \mathrm{Al}^{3+}(aq) + 3 \mathrm{H_2O}(l) \] The net ionic equation shows the reactants and products directly involved in the reaction.

Step 4: Reaction with Magnesium Hydroxide

Magnesium hydroxide, \( \mathrm{Mg(OH)_2(s)} \), reacts similarly: \[ \mathrm{Mg(OH)_2(s)} + 2 \mathrm{H}^{+}(aq) \rightarrow \mathrm{Mg}^{2+}(aq) + 2 \mathrm{H_2O}(l) \] Here, the net ionic equation highlights the transformation of the solid base and dissolved acid to aqueous ions and water.

Step 5: Reaction with Magnesium Carbonate

Magnesium carbonate, \( \mathrm{MgCO_3(s)} \), not only neutralizes the acid but also releases \( \mathrm{CO_2} \) gas: \[ \mathrm{MgCO_3(s)} + 2 \mathrm{H}^{+}(aq) \rightarrow \mathrm{Mg}^{2+}(aq) + \mathrm{CO_2(g)} + \mathrm{H_2O}(l) \] This net ionic equation accounts for the water and carbon dioxide produced.

Step 6: Reaction with Sodium Aluminum Carbonate Hydroxide

For \( \mathrm{NaAl(CO_3)(OH)_2(s)} \), the reaction is more complex but follows similar principles: \[ \mathrm{NaAl(CO_3)(OH)_2(s)} + 4 \mathrm{H}^{+}(aq) \rightarrow \mathrm{Na}^{+}(aq) + \mathrm{Al}^{3+}(aq) + \mathrm{CO_2(g)} + 3 \mathrm{H_2O}(l) \] Even though \( \mathrm{NaCl} \) forms, sodium is a spectator ion.

Step 7: Reaction with Calcium Carbonate

When \( \mathrm{CaCO_3(s)} \) reacts with the acid, carbon dioxide and water are also formed: \[ \mathrm{CaCO_3(s)} + 2 \mathrm{H}^{+}(aq) \rightarrow \mathrm{Ca}^{2+}(aq) + \mathrm{CO_2(g)} + \mathrm{H_2O}(l) \] The key ions and resulting products are illustrated in this net ionic equation.

Key Concepts

Acid-Base Reactions

Acid-base reactions are chemical processes where an acid and a base interact to form water and sometimes a salt. These reactions are fundamental in chemistry and are commonly seen in our daily lives.
In these reactions, acids release hydrogen ions (\( \mathrm{H^+} \)) in solution, while bases contribute hydroxide ions (\( \mathrm{OH^-} \)). When an acid and a base react, the hydrogen ions from the acid combine with the hydroxide ions from the base to create water (\( \mathrm{H_2O} \)). This neutralization process reduces the acidity or basicity of the solution.
Notably, in the stomach, hydrochloric acid (\( \mathrm{HCl} \)) often reacts with antacid bases to relieve discomfort and maintain a neutral pH. Focusing on the ions that participate directly in the acid-base reaction is a critical part of writing net ionic equations. It highlights only the essential participants, ignoring any spectator ions which do not take part in the chemical change.

Antacids

Antacids are substances that help neutralize stomach acid and provide relief from indigestion, heartburn, or ulcers. These compounds are usually weak bases that react with hydrochloric acid in the stomach.
Common antacids include aluminum hydroxide, magnesium hydroxide, and calcium carbonate. Each of these substances, when ingested, reacts with the acid to form water and neutral salts. For example:

• Aluminum hydroxide forms aluminum ions and water.
• Magnesium hydroxide yields magnesium ions and water.
• Calcium carbonate produces calcium ions, water, and carbon dioxide gas, which may lead to burping.

Understanding how these antacids work can help in selecting the right one for specific digestive issues. Furthermore, they demonstrate practical examples of how acid-base reactions function.

Chemical Reactions

Chemical reactions are processes where substances, called reactants, change into new substances, called products. These transformations involve the breaking and forming of chemical bonds, often resulting in visible changes such as gas production, color change, or temperature shift.
A great example is the reaction of antacids with hydrochloric acid in the stomach. These reactions often result in the formation of new compounds and sometimes gases, like carbon dioxide in the case of carbonate antacids.
Most importantly, understanding chemical reactions requires knowledge of the reactants involved, the conditions under which they react, and the products that are formed. The net ionic equations focus on the actual particles that change during the reaction, excluding the so-called 'spectator ions' that remain unaltered. This streamlined view highlights the core of the chemical process.

Balanced Equations

Balanced equations are a representation of chemical reactions where the number of atoms for each element in the reactants equals the number of atoms in the products. This balance adheres to the Law of Conservation of Mass, which states that mass cannot be created or destroyed in a chemical reaction.
Writing balanced equations is crucial to accurately describe chemical processes, ensuring that the same number of each type of atom appears on both sides of the equation.

• For acid-base reactions, balancing equations ensures that all hydrogen or hydroxide ions are accounted for, resulting in correct stoichiometry.
• Balancing can involve adjusting coefficients (the numbers before compounds) but never changing the actual chemical formulas of the substances involved.

A balanced equation ensures clear communication of what exactly occurs in a reaction, valuable both for theoretical work and practical applications like determining the amount of antacid needed to neutralize a certain amount of stomach acid.