Problem 112 - Chemistry: An Atoms-Focused Approach

Question

Antacid Tablets Antacids contain a variety of bases such as \(\mathrm{NaHCO}_{3}, \mathrm{MgCO}_{3}, \mathrm{CaCO}_{3},\) and \(\mathrm{Mg}(\mathrm{OH})_{2} .\) Only \(\mathrm{NaHCO}_{3}\) has appreciable solubility in water. a. Write a net ionic equation for the reaction of each base with aqueous HCl. b. Explain how substances sparingly soluble in water can act as effective antacids.

Step-by-Step Solution

Answer

Short Answer: Sparingly soluble antacids can effectively neutralize stomach acid due to their ability to react with hydrochloric acid (HCl) even in small amounts and produce harmless reaction products, such as water and carbon dioxide gas. The reaction continues as more of the sparingly soluble base becomes exposed to the stomach acid, and the production of harmless by-products allows for easy expulsion from the body.

Step 1: 1. Reaction of NaHCO3 with HCl

The balanced reaction equation of \(\mathrm{NaHCO}_{3}\) with aqueous HCl is given by: $$\mathrm{NaHCO}_{3}(s) + \mathrm{HCl}(aq) \rightarrow \mathrm{NaCl}(aq) + \mathrm{H}_{2}\mathrm{O}(l) + \mathrm{CO}_{2}(g)$$ All compounds are either in an aqueous or gaseous state already, so the net ionic equation would be the same as the balanced reaction equation. $$\mathrm{NaHCO}_{3}(s) + \mathrm{HCl}(aq) \rightarrow \mathrm{NaCl}(aq) + \mathrm{H}_{2}\mathrm{O}(l) + \mathrm{CO}_{2}(g)$$

Step 2: 2. Reaction of MgCO3 with HCl

The balanced reaction equation of \(\mathrm{MgCO}_{3}\) with aqueous HCl is given by: $$\mathrm{MgCO}_{3}(s) + 2\,\mathrm{HCl}(aq) \rightarrow \mathrm{MgCl}_{2}(aq) + \mathrm{H}_{2}\mathrm{O}(l) + \mathrm{CO}_{2}(g)$$ All compounds are either in an aqueous or gaseous state already, so the net ionic equation would be the same as the balanced reaction equation. $$\mathrm{MgCO}_{3}(s) + 2\,\mathrm{HCl}(aq) \rightarrow \mathrm{MgCl}_{2}(aq) + \mathrm{H}_{2}\mathrm{O}(l) + \mathrm{CO}_{2}(g)$$

Step 3: 3. Reaction of CaCO3 with HCl

The balanced reaction equation of \(\mathrm{CaCO}_{3}\) with aqueous HCl is given by: $$\mathrm{CaCO}_{3}(s) + 2\,\mathrm{HCl}(aq) \rightarrow \mathrm{CaCl}_{2}(aq) + \mathrm{H}_{2}\mathrm{O}(l) + \mathrm{CO}_{2}(g)$$ All compounds are either in an aqueous or gaseous state already, so the net ionic equation would be the same as the balanced reaction equation. $$\mathrm{CaCO}_{3}(s) + 2\,\mathrm{HCl}(aq) \rightarrow \mathrm{CaCl}_{2}(aq) + \mathrm{H}_{2}\mathrm{O}(l) + \mathrm{CO}_{2}(g)$$

Step 4: 4. Reaction of Mg(OH)2 with HCl

The balanced reaction equation of \(\mathrm{Mg}(\mathrm{OH})_{2}\) with aqueous HCl is given by: $$\mathrm{Mg}(\mathrm{OH})_{2}(s) + 2\,\mathrm{HCl}(aq) \rightarrow \mathrm{MgCl}_{2}(aq) + 2\,\mathrm{H}_{2}\mathrm{O}(l)$$ All compounds are either in an aqueous or gaseous state already, so the net ionic equation would be the same as the balanced reaction equation. $$\mathrm{Mg}(\mathrm{OH})_{2}(s) + 2\,\mathrm{HCl}(aq) \rightarrow \mathrm{MgCl}_{2}(aq) + 2\,\mathrm{H}_{2}\mathrm{O}(l)$$ b. Explanation of the effectiveness of sparingly soluble antacids

Step 5: Understanding solubility and reaction with HCl

Even though some of these bases are sparingly soluble in water, they can still react with the hydrochloric acid (HCl) present in the stomach. When the antacid tablets come into contact with the stomach acid, the soluble part of the base will dissolve and react with the acid to neutralize it. As it dissolves, more of the sparingly soluble base becomes exposed to the stomach acid, allowing the reaction to continue until either the base or the acid is used up.

Step 6: Importance of the reaction products

The reaction products in most cases are water and a gas (CO2), which helps to decrease the acidity of the stomach contents without adding any significant volume or creating harmful by-products. This is one of the reasons for using sparingly soluble bases as antacids, as they not only neutralize the acid but also produce harmless products that can be easily expelled from the body. Overall, sparingly soluble antacids can effectively neutralize stomach acid due to their ability to react with HCl even in small amounts, and their production of harmless reaction products.

Key Concepts

Net Ionic Equations

Net ionic equations focus on the active participants in a chemical reaction. In acid-base reactions, these equations help illustrate which ions are involved in forming new substances. This provides a clearer picture of the chemical changes occurring during the reaction.
Antacids often contain bases that react with stomach acid, typically hydrochloric acid (HCl). As shown in equations with \(\mathrm{NaHCO}_3\), \(\mathrm{MgCO}_3\), and \(\mathrm{CaCO}_3\), these reactions produce water, carbon dioxide, and salts like \(\mathrm{NaCl}\) or \(\mathrm{MgCl}_2\). The consistent net ionic equations demonstrate how different bases neutralize \(\mathrm{HCl}\) by primarily involving the release of carbonate ions to form carbonic acid, then decomposing into carbon dioxide and water.
For example: The net ionic equation for the reaction of \(\mathrm{CaCO}_3\) with HCl shows only the important players: - \(\mathrm{CaCO}_3(s)\) + 2\(\mathrm{H}^+(aq)\) \(\rightarrow\) \(\mathrm{Ca}^{2+}(aq)\) + \(\mathrm{H}_2\mathrm{O}(l)\) + \(\mathrm{CO}_2(g)\).
This simplicity allows chemists to understand reactions efficiently without the complexity of spectator ions.

Sparingly Soluble Bases

Some antacids contain sparingly soluble bases like \(\mathrm{MgCO}_3\) or \(\mathrm{CaCO}_3\), meaning they don't dissolve completely in water. Despite this, they are effective in neutralizing stomach acid due to their basic properties. The partial solubility allows these bases to gradually dissolve and react with stomach acids like \(\mathrm{HCl}\).
As these bases contact the acidic environment of the stomach, they begin to dissolve. The acid reacts with available base ions, reducing its own acidity. The reaction continues as more base dissolves until all the soluble content is utilized or the stomach's acid is neutralized.

• The reaction with \(\mathrm{HCl}\) generates salt, water, and carbon dioxide.
• This gas release can be noticed as burps, aiding in discomfort relief.

The controlled dissolution is beneficial, ensuring a steady release and action, making these antacids an efficient choice even with limited solubility.

Antacid Effectiveness

The effectiveness of antacids in countering excess stomach acid is a key concern. Antacids attack the root cause of acidity by neutralizing \(\mathrm{HCl}\) in the stomach. This neutralization not only reduces acidity but also minimizes symptoms like heartburn.
Sparingly soluble bases in antacids provide several advantages:

• They allow for a gradual neutralization process, which is gentler on the stomach.
• They produce harmless byproducts like carbon dioxide and water, avoiding complications associated with other treatments.

These reactions involve the conversion of harmful excess acid into benign substances, making antacids a safe and effective treatment option. The choice of particular bases, such as \(\mathrm{NaHCO}_3\), \(\mathrm{MgCO}_3\), and \(\mathrm{CaCO}_3\), ensures a range of dissolution rates and acid-neutralizing capacities, tailored to different needs and preferences. This versatile approach addresses not just the symptoms but also the underlying excess acid, providing comprehensive relief and protection for the digestive system.