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: (a) \(\mathrm{Al}(\mathrm{OH})_{3}(\mathrm{s}),\) (b) \(\mathrm{Mg}(\mathrm{OH})_{2}(\mathrm{s})\), \((\mathbf{c}) \mathrm{MgCO}_{3}(s)\), \((\mathbf{d}) \mathrm{NaAl}\left(\mathrm{CO}_{3}\right)(\mathrm{OH})_{2}(s),\) (e) \(\mathrm{CaCO}_{3}(\mathrm{s}).\)

Short answer

The balanced net ionic equations for the reactions between aqueous HCl and the given antacid substances are: (a) Al(OH)\(_3\)(s) + 3H\(^+\)(aq) → Al\(^{3+}\)(aq) + 3H\(_2\)O(l) (b) Mg(OH)\(_2\)(s) + 2H\(^+\)(aq) → Mg\(^{2+}\)(aq) + 2H\(_2\)O(l) (c) MgCO\(_3\)(s) + 2H\(^+\)(aq) → Mg\(^{2+}\)(aq) + H\(_2\)O(l) + CO\(_2\)(g) (d) NaAl(CO\(_3\))(OH)\(_2\)(s) + 6H\(^+\)(aq) → 3H\(_2\)O(l) + Al\(^{3+}\)(aq) + 2CO\(_2\)(g) (e) CaCO\(_3\)(s) + 2H\(^+\)(aq) → Ca\(^{2+}\)(aq) + H\(_2\)O(l) + CO\(_2\)(g)

Step-by-step solution

Write the Balanced Overall Chemical Equations

First, we will write the balanced overall chemical equations for the reaction between each antacid substance and the aqueous HCl in the stomach. (a) Al(OH)\(_3\)(s) + 3HCl(aq) → AlCl\(_3\)(aq) + 3H\(_2\)O(l) (b) Mg(OH)\(_2\)(s) + 2HCl(aq) → MgCl\(_2\)(aq) + 2H\(_2\)O(l) (c) MgCO\(_3\)(s) + 2HCl(aq) → MgCl\(_2\)(aq) + H\(_2\)O(l) + CO\(_2\)(g) (d) NaAl(CO\(_3\))(OH)\(_2\)(s) + 6HCl(aq) → 3H\(_2\)O(l) + 2NaCl(aq) + AlCl\(_3\)(aq) + 2CO\(_2\)(g) (e) CaCO\(_3\)(s) + 2HCl(aq) → CaCl\(_2\)(aq) + H\(_2\)O(l) + CO\(_2\)(g)

Write the Net Ionic Equations

Now we will identify and remove the spectator ions (ions that do not participate in the chemical reaction) from the balanced overall chemical equations and write the net ionic equations for each reaction. (a) Net Ionic Equation: Al(OH)\(_3\)(s) + 3H\(^+\)(aq) → Al\(^{3+}\)(aq) + 3H\(_2\)O(l) (b) Net Ionic Equation: Mg(OH)\(_2\)(s) + 2H\(^+\)(aq) → Mg\(^{2+}\)(aq) + 2H\(_2\)O(l) (c) Net Ionic Equation: MgCO\(_3\)(s) + 2H\(^+\)(aq) → Mg\(^{2+}\)(aq) + H\(_2\)O(l) + CO\(_2\)(g) (d) Net Ionic Equation: NaAl(CO\(_3\))(OH)\(_2\)(s) + 6H\(^+\)(aq) → 3H\(_2\)O(l) + Al\(^{3+}\)(aq) + 2CO\(_2\)(g) (e) Net Ionic Equation: CaCO\(_3\)(s) + 2H\(^+\)(aq) → Ca\(^{2+}\)(aq) + H\(_2\)O(l) + CO\(_2\)(g)

Key concepts

Chemical Reactions

Understanding chemical reactions is a foundational concept in chemistry. A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the movement of electrons in the forming and breaking of chemical bonds.

During these reactions, the reactants are converted to products, and these changes are represented by chemical equations. Chemical reactions can be further categorized into types, such as synthesis, decomposition, single replacement, double replacement, and combustion. The transformation involves the rearrangement of atoms, and no new atoms are created or destroyed in the process. For students, visualizing the process through balanced equations and pictorial representations can help in grasping the fundamental concept of conservation of mass in chemical reactions.

Antacids and HCl Reaction

The reaction between antacids and hydrochloric acid (HCl) in the stomach is an important chemical reaction that helps neutralize stomach acidity. Antacids are substances that counteract the acidity of the stomach by increasing the pH.

Antacids typically contain basic compounds like Al(OH)₃, Mg(OH)₂, MgCO₃, NaAl(CO₃)(OH)₂, or CaCO₃, which can neutralize stomach acid by reacting with HCl to produce salts, water, and sometimes carbon dioxide. For instance, Mg(OH)₂ reacts with HCl to produce MgCl₂ and water. This helps to alleviate symptoms associated with high stomach acidity like heartburn or gastric ulcers.

Balancing Chemical Equations

The process of balancing chemical equations is crucial to accurately represent a chemical reaction. A balanced chemical equation ensures the law of conservation of mass is obeyed; that is, the same number of atoms for each element is present on both the reactant and the product side of the equation.

When balancing an equation, one must adjust the coefficients (the numbers before the chemical formulas) to ensure this balance. For example, if the reaction involves one aluminum atom on the reactant side, then there should be one aluminum atom on the product side as well. Balancing equations is a skill that requires practice. It's worthwhile to start with individual elements that appear in only one reactant and one product before moving on to those that are in multiple substances.

Aqueous Solutions and Solubility

In chemistry, an aqueous solution is a solution in which the solvent is water. It's usually shown in a chemical equation by appending (aq) to the relevant formula. Solubility is a property referring to the ability for a given substance, the solute, to dissolve in a solvent.

The concept of solubility is particularly important when writing net ionic equations, which often involve the reaction of substances initially dissolved in water. For instance, when salts dissolve in water they dissociate into ions, which can then participate in chemical reactions. The solubility rules help predict whether a compound will dissolve in water, and this is essential for determining the complete ionic equation from which the net ionic equation is derived. By understanding solubility, students can better grasp how and why certain reactions occur in aqueous solutions.