Problem 102 - Chemistry An Atoms First Approach

Question

Some of the substances commonly used in stomach antacids are \(\mathrm{MgO}, \mathrm{Mg}(\mathrm{OH})_{2},\) and \(\mathrm{Al}(\mathrm{OH})_{3}\) a. Write a balanced equation for the neutralization of hydrochloric acid by each of these substances. b. Which of these substances will neutralize the greatest amount of 0.10 \(M\) HCl per gram?

Step-by-Step Solution

Answer

a. The balanced equations for the neutralization of hydrochloric acid by MgO, Mg(OH)₂, and Al(OH)₃ are: 1. MgO + 2HCl → MgCl₂ + H₂O 2. Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O 3. Al(OH)₃ + 3HCl → AlCl₃ + 3H₂O b. Comparing moles of HCl neutralized per gram of each substance: - MgO: 0.0496 mol HCl/g - Mg(OH)₂: 0.0343 mol HCl/g - Al(OH)₃: 0.0385 mol HCl/g MgO neutralizes the greatest amount of 0.10 M HCl per gram and is therefore the most effective antacid among these three substances.

Step 1: Write balanced chemical equations for the antacid substances with HCl

To write the balanced equations, we need to combine each antacid substance with hydrochloric acid (HCl) and balance the resulting equation. a. The reactions are: 1. Magnesium oxide (MgO) + hydrochloric acid (HCl): MgO + 2HCl → MgCl₂ + H₂O 2. Magnesium hydroxide (Mg(OH)₂) + hydrochloric acid (HCl): Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O 3. Aluminum hydroxide (Al(OH)₃) + hydrochloric acid (HCl): Al(OH)₃ + 3HCl → AlCl₃ + 3H₂O

Step 2: Calculate the moles of HCl neutralized per gram of each substance

To do this, we need to analyze the previously balanced equations and find out the ratio of moles of HCl neutralized to the moles of each antacid substance. Then, we will find the molar mass of each substance and calculate the moles of HCl neutralized per gram of the substance. 1. MgO: - The balanced equation shows that 1 mole of MgO neutralizes 2 moles of HCl. - Molar mass of MgO = (24.31 g/mol for Mg) + (16.00 g/mol for O) = 40.31 g/mol - Moles of HCl neutralized per gram of MgO = (2 moles HCl)/(40.31 g MgO) = 0.0496 mol HCl/g 2. Mg(OH)₂: - The balanced equation shows that 1 mole of Mg(OH)₂ neutralizes 2 moles of HCl. - Molar mass of Mg(OH)₂ = (24.31 g/mol for Mg) + (2 x 17.01 g/mol for OH) = 58.33 g/mol - Moles of HCl neutralize per gram of Mg(OH)₂ = (2 moles HCl)/(58.33 g Mg(OH)₂) = 0.0343 mol HCl/g 3. Al(OH)₃: - The balanced equation shows that 1 mole of Al(OH)₃ neutralizes 3 moles of HCl. - Molar mass of Al(OH)₃ = (26.98 g/mol for Al) + (3 x 17.01 g/mol for OH) = 78.00 g/mol - Moles of HCl neutralize per gram of Al(OH)₃ = (3 moles HCl)/(78.00 g Al(OH)₃) = 0.0385 mol HCl/g

Step 3: Determine which substance neutralizes the greatest amount of 0.10 M HCl per gram

Now that we have the moles of HCl neutralized per gram of each substance, we can compare the values and determine the most effective antacid. Moles of HCl neutralized per gram: - MgO: 0.0496 mol HCl/g - Mg(OH)₂: 0.0343 mol HCl/g - Al(OH)₃: 0.0385 mol HCl/g MgO neutralizes the greatest amount of 0.10 M HCl per gram. Therefore, MgO is the most effective antacid among the three substances.

Key Concepts

Chemical Equations

Chemical equations are expressions that describe the chemical reactions between different substances. In these equations, reactants are the substances that interact, while products are the new substances formed. Writing a chemical equation involves identifying the reactants and products and balancing the equation so that the same number of each type of atom appears on both sides of the equation.
Balancing chemical equations is crucial for demonstrating the Law of Conservation of Mass, which states that mass is neither created nor destroyed in a chemical reaction.

• For instance, the reaction between magnesium oxide and hydrochloric acid is: \[ \text{MgO} + 2\text{HCl} \rightarrow \text{MgCl}_2 + \text{H}_2\text{O} \] This is balanced because the same number of each type of atom is on both sides.
• Similarly, the reaction involving magnesium hydroxide is: \[ \text{Mg(OH)}_2 + 2\text{HCl} \rightarrow \text{MgCl}_2 + 2\text{H}_2\text{O} \]
• Lastly, the equation for aluminum hydroxide is: \[ \text{Al(OH)}_3 + 3\text{HCl} \rightarrow \text{AlCl}_3 + 3\text{H}_2\text{O} \]

Each equation must be carefully balanced, ensuring that both sides reflect the same quantity of atoms, illustrating how substances transform during reactions.

Molar Mass Calculation

Molar mass is the weight of one mole of a substance and is measured in grams per mole (g/mol). It is an essential concept in chemistry because it allows us to relate the mass of a substance to the number of particles it contains.
To calculate the molar mass, one must sum the atomic masses of each element in the formula of a compound.

• For magnesium oxide (MgO), the molar mass is the sum of magnesium (24.31 g/mol) and oxygen (16.00 g/mol), resulting in a molar mass of 40.31 g/mol.
• Magnesium hydroxide (Mg(OH)₂) requires calculating magnesium and two hydroxide groups, each consisting of oxygen and hydrogen, leading to a molar mass of 58.33 g/mol.
• For aluminum hydroxide (Al(OH)₃), the molar masses of aluminum and three hydroxide groups are added together, resulting in 78.00 g/mol.

Understanding how to compute molar mass enables one to convert between grams and moles, facilitating stoichiometric calculations in chemical reactions.

Antacids

Antacids are medications that counteract stomach acid, providing relief from heartburn and indigestion. They function by neutralizing the hydrochloric acid (HCl) present in the stomach, increasing the pH level to relieve discomfort.
Common antacid substances include magnesium oxide, magnesium hydroxide, and aluminum hydroxide. Each of these compounds engages in a chemical reaction with hydrochloric acid as follows:

• Magnesium oxide: Reacts with hydrochloric acid to form magnesium chloride and water.
• Magnesium hydroxide: Converts to magnesium chloride and water upon reaction.
• Aluminum hydroxide: Transforms to aluminum chloride and water during its reaction with HCl.

These reactions highlight the ability of antacids to neutralize stomach acid effectively, making them a useful tool in managing symptoms related to excess stomach acid.

HCl Neutralization

HCl neutralization is an important process, typically involving a reaction between hydrochloric acid and a base or antacid. The objective is to lower the acidity by forming a salt and water, thereby increasing the pH.
The effectiveness of an antacid in neutralizing HCl is determined by calculating the moles of HCl that a certain mass of antacid can neutralize.

• Magnesium oxide: One mole neutralizes two moles of HCl, leading to a neutralization capability of 0.0496 mol HCl per gram.
• Magnesium hydroxide: Similarly neutralizes two moles of HCl per mole, with a neutralization capacity of 0.0343 mol HCl per gram.
• Aluminum hydroxide: With its ability to neutralize three moles of HCl per mole, it neutralizes 0.0385 mol HCl per gram.

These calculations demonstrate that magnesium oxide is the most effective, neutralizing the greatest amount of HCl per gram, emphasizing the practical applications of these principles in choosing effective antacids.