Question

Every antacid contains one or more ingredients capable of reacting with excess stomach acid (HCl). The essential neutralization products are \(\mathrm{CO}_{2}\) and/ or \(\mathrm{H}_{2} \mathrm{O} .\) Write net ionic equations to represent the neutralizing action of the following popular antacids. (a) Alka-Seltzer (sodium bicarbonate) (b) Tums (calcium carbonate) (c) milk of magnesia (magnesium hydroxide) (d) Maalox (magnesium hydroxide, aluminum hydroxide) (e) Rolaids \(\left[\mathrm{NaAl}(\mathrm{OH})_{2} \mathrm{CO}_{3}\right]\)

Short answer

The net ionic equations for the antacids are: (a) \(\mathrm{HCO}_{3}^{-}(aq) + \mathrm{H}^{+}(aq) \rightarrow \mathrm{H}_{2}\mathrm{O}(l) + \mathrm{CO}_{2}(g)\), (b) \(\mathrm{CO}_{3}^{2-}(aq) + 2 \mathrm{H}^{+}(aq) \rightarrow \mathrm{H}_{2}\mathrm{O}(l) + \mathrm{CO}_{2}(g)\), (c) \(\mathrm{OH}^{-}(aq) + \mathrm{H}^{+}(aq) \rightarrow \mathrm{H}_{2}\mathrm{O}(l)\), (d) \(\mathrm{OH}^{-}(aq) + \mathrm{H}^{+}(aq) \rightarrow \mathrm{H}_{2}\mathrm{O}(l)\), (e) The reaction could be broken into two steps and result in neutralization with water and carbon dioxide. In all of them, stomach acid is neutralized producing water and in some cases carbon dioxide.

Step-by-step solution

Writing Net Ionic Equation for Alka-Seltzer

Alka-Seltzer contains sodium bicarbonate (NaHCO3). The reaction of sodium bicarbonate and hydrochloric acid (HCl) can be written as follows: \[ \mathrm{NaHCO}_{3}(s) + \mathrm{HCl}(aq) \rightarrow \mathrm{NaCl}(aq) + \mathrm{H}_{2}\mathrm{O}(l) + \mathrm{CO}_{2}(g) \] The net ionic equation, showing only species that actually participate in the reaction, will therefore be: \[ \mathrm{HCO}_{3}^{-}(aq) + \mathrm{H}^{+}(aq) \rightarrow \mathrm{H}_{2}\mathrm{O}(l) + \mathrm{CO}_{2}(g) \]

Writing Net Ionic Equation for Tums

Tums contains calcium carbonate (CaCO3). The reaction of calcium carbonate and hydrochloric acid can be written as follows: \[ \mathrm{CaCO}_{3}(s) + 2 \mathrm{HCl}(aq) \rightarrow \mathrm{CaCl}_{2}(aq) + \mathrm{H}_{2}\mathrm{O}(l) + \mathrm{CO}_{2}(g) \] The net ionic equation will therefore be: \[ \mathrm{CO}_{3}^{2-}(aq) + 2 \mathrm{H}^{+}(aq) \rightarrow \mathrm{H}_{2}\mathrm{O}(l) + \mathrm{CO}_{2}(g) \]

Writing Net Ionic Equation for Milk of Magnesia

Milk of Magnesia contains magnesium hydroxide (Mg(OH)2). The reaction of magnesium hydroxide and hydrochloric acid is: \[ \mathrm{Mg(OH)}_{2}(s) + 2 \mathrm{HCl}(aq) \rightarrow \mathrm{MgCl}_{2}(aq) + 2 \mathrm{H}_{2}\mathrm{O}(l) \] The net ionic equation is reduced to: \[ \mathrm{OH}^{-}(aq) + \mathrm{H}^{+}(aq) \rightarrow \mathrm{H}_{2}\mathrm{O}(l) \]

Writing Net Ionic Equation for Maalox

Maalox contains magnesium hydroxide and aluminum hydroxide (Al(OH)3). However, for the purpose of this exercise and to keep it straightforward, the net ionic equation, as with magnesium hydroxide in milk of magnesia, for the reaction with stomach acid is: \[ \mathrm{OH}^{-}(aq) + \mathrm{H}^{+}(aq) \rightarrow \mathrm{H}_{2}\mathrm{O}(l) \]

Writing Net Ionic Equation for Rolaids

Rolaids contains sodium aluminate (NaAl(OH)2CO3). The net ionic equation for its reaction with hydrochloric acid is somewhat complex due to the presence of three different ions in the formula. However, for simplicity, this could be broken down into two steps with the resulting net ionic equation being similar to the one in Step 1 related to sodium bicarbonate and in Step 4 related to hydroxide ions.

Key concepts

Antacids

Antacids are over-the-counter medications that help relieve symptoms of heartburn, indigestion, or an upset stomach. They work by neutralizing excess gastric acid in the stomach, which helps to alleviate discomfort.

• The primary function of antacids is to reduce acidity in the stomach, preventing acid reflux and soothing the stomach lining.


• Common ingredients in antacids include substances like sodium bicarbonate, calcium carbonate, magnesium hydroxide, and aluminum hydroxide.


• These compounds target hydrochloric acid (HCl) in the stomach, reacting with it to form neutral products, such as water and carbon dioxide.

Different antacids vary in their composition and effectiveness. Some provide immediate relief, while others are intended for longer-lasting effects. Understanding which ingredients are present in specific antacids can help you select the right product for your needs.

Stomach Acid Neutralization

Stomach acid neutralization is the process by which antacids decrease the acidity of the gastric juices in your stomach. This is done through a chemical reaction with hydrochloric acid (HCl), the main component of stomach acid.

• The gastric juices in the stomach contain HCl, which has a very low pH, making them highly acidic and crucial for digesting food.


• During digestion, if excessive acid is produced, it can lead to discomfort; this is where stomach acid neutralization comes into play.

When an antacid is ingested, it reacts with the excess HCl:

• This reaction generally produces a salt, water, and in some cases carbon dioxide.


• The result is a less acidic environment in the stomach, which eases symptoms of indigestion and heartburn.

Stomach acid neutralization is a straightforward solution for immediate relief from acid-related discomforts.

Hydrochloric Acid Reactions

Reactions involving hydrochloric acid are central to the function of antacids. Each reaction involves a proton exchange where the HCl donates a hydrogen ion (H⁺) to a base found within the antacid.

• For instance, when HCl reacts with sodium bicarbonate (NaHCO₃), it forms sodium chloride (NaCl), water ( H₂O), and carbon dioxide ( CO₂).


• In the case of calcium carbonate ( CaCO₃), HCl combines to form calcium chloride ( CaCl₂), with water and carbon dioxide as by-products.

These reactions are double displacement reactions in aqueous solutions. The products are more neutral compared to the acidic reactants, supporting the neutralization process. Through these interactions, the antacids successfully perform their role of reducing stomach acidity by turning corrosive acid into harmless substances.

Chemical Reactions in Aqueous Solutions

Chemical reactions that occur in aqueous solutions involve reactants dissolved in water, making ions available to participate in reactions. These types of reactions include acid-base reactions, which antacids utilize to neutralize stomach acid.

• In aqueous solutions, ionic compounds break apart into individual ions. For instance, HCl dissociates to form H⁺ and Cl⁻ ions.


• The key feature of these reactions is the combination and recombination of ions to form new products.

In the context of antacid reactions:

• The neutralization reactions occur when hydroxide ions ( OH⁻) or carbonate ions ( CO₃²⁻) from the antacid join with the hydrogen ions ( H⁺) from the stomach acid.


• These interactions form neutral water molecules ( H₂O) or neutral gases like carbon dioxide ( CO₂).

Understanding these types of reactions helps in grasping how antacids are effective in treating symptoms related to high stomach acidity.