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

Step-by-Step Solution

Answer

The net ionic equations for the reaction of HCl(aq) with the given antacids are: (a) \(\mathrm{Al(OH)_{3}(s)} + 3\mathrm{H^+(aq)} \rightarrow \mathrm{Al^{3+}(aq)} + 3\mathrm{H_{2}O(l)}\) (b) \(\mathrm{Mg(OH)_{2}(s)} + 2\mathrm{H^+(aq)} \rightarrow \mathrm{Mg^{2+}(aq)} + 2\mathrm{H_{2}O(l)}\) (c) \(\mathrm{MgCO_{3}(s)} + 2\mathrm{H^+(aq)} \rightarrow \mathrm{Mg^{2+}(aq)} + \mathrm{H_{2}O(l)} + \mathrm{CO_{2}(g)}\) (d) \(2\mathrm{NaAl(CO_{3})(OH)_{2}(s)} + 6\mathrm{H^+(aq)} \rightarrow 2\mathrm{Na^+(aq)} + 2\mathrm{Al^{3+}(aq)} + 4\mathrm{H_{2}O(l)} + 2\mathrm{CO_{2}(g)}\) (e) \(\mathrm{CaCO_{3}(s)} + 2\mathrm{H^+(aq)} \rightarrow \mathrm{Ca^{2+}(aq)} + \mathrm{H_{2}O(l)} + \mathrm{CO_{2}(g)}\)

Step 1: 1. Write the balanced chemical equation

Here are the balanced chemical equations for each reaction: (a) \(\mathrm{Al(OH)_{3}(s)} + 3\mathrm{HCl(aq)} \rightarrow \mathrm{AlCl_{3}(aq)} + 3\mathrm{H_{2}O(l)}\) (b) \(\mathrm{Mg(OH)_{2}(s)} + 2\mathrm{HCl(aq)} \rightarrow \mathrm{MgCl_{2}(aq)} + 2\mathrm{H_{2}O(l)}\) (c) \(\mathrm{MgCO_{3}(s)} + 2\mathrm{HCl(aq)} \rightarrow \mathrm{MgCl_{2}(aq)} + \mathrm{H_{2}O(l)} + \mathrm{CO_{2}(g)}\) (d) \(2\mathrm{NaAl(CO_{3})(OH)_{2}(s)} + 6\mathrm{HCl(aq)} \rightarrow 2\mathrm{NaCl(aq)} + 2\mathrm{AlCl_{3}(aq)} + 4\mathrm{H_{2}O(l)} + 2\mathrm{CO_{2}(g)}\) (e) \(\mathrm{CaCO_{3}(s)} + 2\mathrm{HCl(aq)} \rightarrow \mathrm{CaCl_{2}(aq)} + \mathrm{H_{2}O(l)} + \mathrm{CO_{2}(g)}\)

Step 2: 2. Separate aqueous ions

Now, we break down each aqueous solution into their respective ions: (a) \(\mathrm{Al(OH)_{3}(s)} + 3\mathrm{H^+(aq)} + 3\mathrm{Cl^-(aq)} \rightarrow \mathrm{Al^{3+}(aq)} + 3\mathrm{Cl^-(aq)} + 3\mathrm{H_{2}O(l)}\) (b) \(\mathrm{Mg(OH)_{2}(s)} + 2\mathrm{H^+(aq)} + 2\mathrm{Cl^-(aq)} \rightarrow \mathrm{Mg^{2+}(aq)} + 2\mathrm{Cl^-(aq)} + 2\mathrm{H_{2}O(l)}\) (c) \(\mathrm{MgCO_{3}(s)} + 2\mathrm{H^+(aq)} + 2\mathrm{Cl^-(aq)} \rightarrow \mathrm{Mg^{2+}(aq)} + 2\mathrm{Cl^-(aq)} + \mathrm{H_{2}O(l)} + \mathrm{CO_{2}(g)}\) (d) \(2\mathrm{NaAl(CO_{3})(OH)_{2}(s)} + 6\mathrm{H^+(aq)} + 6\mathrm{Cl^-(aq)} \rightarrow 2\mathrm{Na^+(aq)} + 2\mathrm{Cl^-(aq)} + 2\mathrm{Al^{3+}(aq)} + 6\mathrm{Cl^-(aq)} + 4\mathrm{H_{2}O(l)} + 2\mathrm{CO_{2}(g)}\) (e) \(\mathrm{CaCO_{3}(s)} + 2\mathrm{H^+(aq)} + 2\mathrm{Cl^-(aq)} \rightarrow \mathrm{Ca^{2+}(aq)} + 2\mathrm{Cl^-(aq)} + \mathrm{H_{2}O(l)} + \mathrm{CO_{2}(g)}\)

Step 3: 3. Cancel out spectator ions

We proceed to cancel out the spectator ions in each equation: (a) \(\cancel{3\mathrm{Cl^-(aq)}}\) (b) \(\cancel{2\mathrm{Cl^-(aq)}}\) (c) \(\cancel{2\mathrm{Cl^-(aq)}}\) (d) \(\cancel{2\mathrm{Cl^-(aq)}}\) and \(\cancel{6\mathrm{Cl^-(aq)}}\) (e) \(\cancel{2\mathrm{Cl^-(aq)}}\)

Step 4: 4. Write net ionic equations

Finally, we write the net ionic equations for each reaction: (a) \(\mathrm{Al(OH)_{3}(s)} + 3\mathrm{H^+(aq)} \rightarrow \mathrm{Al^{3+}(aq)} + 3\mathrm{H_{2}O(l)}\) (b) \(\mathrm{Mg(OH)_{2}(s)} + 2\mathrm{H^+(aq)} \rightarrow \mathrm{Mg^{2+}(aq)} + 2\mathrm{H_{2}O(l)}\) (c) \(\mathrm{MgCO_{3}(s)} + 2\mathrm{H^+(aq)} \rightarrow \mathrm{Mg^{2+}(aq)} + \mathrm{H_{2}O(l)} + \mathrm{CO_{2}(g)}\) (d) \(2\mathrm{NaAl(CO_{3})(OH)_{2}(s)} + 6\mathrm{H^+(aq)} \rightarrow 2\mathrm{Na^+(aq)} + 2\mathrm{Al^{3+}(aq)} + 4\mathrm{H_{2}O(l)} + 2\mathrm{CO_{2}(g)}\) (e) \(\mathrm{CaCO_{3}(s)} + 2\mathrm{H^+(aq)} \rightarrow \mathrm{Ca^{2+}(aq)} + \mathrm{H_{2}O(l)} + \mathrm{CO_{2}(g)}\)

Key Concepts

Antacids

Antacids are essential medications used to neutralize excess stomach acid, providing relief from discomfort and healing minor ulcers. These substances work by neutralizing gastric acidity, primarily by increasing the pH level in the stomach. This reduction in acidity can alleviate symptoms such as heartburn, indigestion, and stomach pain. Some common compounds used in antacids include:

• Aluminum hydroxide,
• Magnesium hydroxide,
• Calcium carbonate.

These compounds react with hydrochloric acid (HCl), which is the main component of stomach acid, to form salts and water. This neutralization reaction is fundamental in the functioning of antacids. Understanding the chemical process behind these reactions will help you appreciate how antacids alleviate symptoms associated with excess stomach acid.

Acid-Base Reactions

Acid-base reactions are chemical processes that involve the transfer of hydrogen ions (H^+). An acid is a substance that can donate a hydrogen ion, while a base is one that can accept it. When acids and bases react, they often produce a salt and water. In a typical antacid reaction, the base (a component of the antacid) reacts with the hydrochloric acid (HCl) in the stomach.For example, when magnesium hydroxide reacts with HCl, the reaction is as follows:\( \text{Mg(OH)}_2 + \text{2HCl} \rightarrow \text{MgCl}_2 + \text{2H}_2\text{O} \)The magnesium hydroxide acts as a base, accepting hydrogen ions from the hydrochloric acid, resulting in the formation of water, a neutral substance, and magnesium chloride, the salt. This type of reaction characterizes the neutralization process provided by antacids.

Chemical Equations

Chemical equations are symbolic representations of chemical reactions. They show the substances involved in the reaction (reactants) and the substances produced (products). Balancing these equations is crucial because it respects the law of conservation of mass, meaning the number of atoms of each element must be the same on both sides of the equation.Consider the reaction between aluminum hydroxide and hydrochloric acid:\( \text{Al(OH)}_3 + \text{3HCl} \rightarrow \text{AlCl}_3 + \text{3H}_2\text{O} \)Here, the equation is balanced as each element has the same number of atoms on both the reactant and product sides. Balancing the chemical equation ensures that we accurately capture the process occurring on a molecular level during the reaction, allowing us to predict the outcome of the reaction precisely.

Spectator Ions

In chemical reactions that occur in aqueous solutions, not all ions participate directly in the reaction. Ions that do not change their oxidation state and remain in the solution unchanged are called spectator ions. They are present to maintain electrical neutrality but do not participate in the chemical change.When writing net ionic equations, spectator ions are removed since they do not influence the reaction. For example, in the reaction between magnesium hydroxide and hydrochloric acid:\( \text{Mg(OH)}_2 + \text{2H}^+ + 2\text{Cl}^- \rightarrow \text{Mg}^{2+} + 2\text{Cl}^- + \text{2H}_2\text{O} \)Chloride ions (Cl^-) are spectator ions because they appear on both sides of the equation and do not affect the reaction significantly. By omitting them, we simplify the equation to reflect only the reacting ions, providing clearer insight into the essential changes.