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?

Short answer

The balanced equations for the neutralization of hydrochloric acid by MgO, Mg(OH)₂, and Al(OH)₃ are: a. \(MgO + 2HCl \to MgCl_{2} + H_{2}O\) b. \(Mg(OH)_{2} + 2HCl \to MgCl_{2} + 2H_{2}O\) c. \(Al(OH)_{3} + 3HCl \to AlCl_{3} + 3H_{2}O\) Moles of HCl neutralized per gram: - MgO: 0.0496 moles HCl/g - Mg(OH)₂: 0.0343 moles HCl/g - Al(OH)₃: 0.0385 moles HCl/g The substance that neutralizes the greatest amount of HCl per gram is MgO, with 0.0496 moles HCl/g.

Step-by-step solution

Write balanced equations for the neutralization

Let's write balanced equations for the neutralization of hydrochloric acid by MgO, Mg(OH)₂, and Al(OH)₃. a. For MgO: \(MgO + 2HCl \to MgCl_{2} + H_{2}O\) b. For Mg(OH)₂: \(Mg(OH)_{2} + 2HCl \to MgCl_{2} + 2H_{2}O\) c. For Al(OH)₃: \(Al(OH)_{3} + 3HCl \to AlCl_{3} + 3H_{2}O\)

Calculate moles of HCl neutralized per gram

To find which of these substances can neutralize the greatest amount of 0.10 M HCl per gram, we'll first need to calculate the number of moles of HCl neutralized per gram of each substance. a. For MgO: Molar mass of MgO: Mg (24.31 g/mol) + O (16.00 g/mol) = 40.31 g/mol Moles of HCl neutralized per gram of MgO: (1 mole MgO / 40.31 g) * 2 moles HCl / 1 mole MgO = 0.0496 moles HCl/g b. For Mg(OH)₂: Molar Mass of Mg(OH)₂: Mg (24.31 g/mol) + 2 * O (16.00 g/mol) + 2 * H (1.01 g/mol) = 58.33 g/mol Moles of HCl neutralized per gram of Mg(OH)₂: (1 mole Mg(OH)₂ / 58.33 g) * 2 moles HCl / 1 mole Mg(OH)₂ = 0.0343 moles HCl/g c. For Al(OH)₃: Molar Mass of Al(OH)₃: Al (26.98 g/mol) + 3 * O (16.00 g/mol) + 3 * H (1.01 g/mol) = 78.01 g/mol Moles of HCl neutralized per gram of Al(OH)₃: (1 mole Al(OH)₃ / 78.01 g) * 3 moles HCl / 1 mole Al(OH)₃ = 0.0385 moles HCl/g

Determine the substance that neutralizes the greatest amount of HCl per gram

Now that we have the moles of HCl neutralized per gram for each substance, we can compare them: MgO: 0.0496 moles HCl/g Mg(OH)₂: 0.0343 moles HCl/g Al(OH)₃: 0.0385 moles HCl/g The substance that neutralizes the greatest amount of HCl per gram is MgO, with 0.0496 moles HCl/g.

Key concepts

Balanced Chemical Equations

A balanced chemical equation is essential for accurately representing a chemical reaction. It shows the exact ratio in which reactants combine to form products. Each chemical equation is like a recipe, ensuring we start with the right amounts to get the desired outcome.

This involves matching the number of atoms for each element on both sides of the equation. For instance, in the neutralization of hydrochloric acid (HCl) with magnesium oxide (MgO), the equation is: \(MgO + 2HCl \to MgCl_2 + H_2O\). Here, we see that one MgO molecule reacts with two HCl molecules.

In another example, neutralizing with magnesium hydroxide (Mg(OH)₂) requires the equation: \(Mg(OH)_2 + 2HCl \to MgCl_2 + 2H_2O\), again noting the two HCl molecules.

Lastly, aluminium hydroxide (Al(OH)₃) follows this balanced equation: \(Al(OH)_3 + 3HCl \to AlCl_3 + 3H_2O\), showing it requires three HCl molecules. Each equation demonstrates how to balance the reactants and products properly.

Stoichiometry

Stoichiometry is the heart of quantitative chemistry. It's the process of calculating the amounts of reactants and products involved in a chemical reaction. Using a balanced chemical equation, stoichiometry helps us determine how much of each reactant is needed and how much product is produced.

This process relies on mole-to-mole conversion from the coefficients in the balanced equations. For instance, consider the equations in our antacid reactions. Each formula, like \(Mg(OH)_2 + 2HCl \to MgCl_2 + 2H_2O\), plainly illustrates that two moles of HCl react with one mole of Mg(OH)₂.

These ratios allow us to translate a chemical reaction into usable data, predicting how much acid can be neutralized. Stoichiometry is incredibly useful in laboratory and industrial applications, as it guides chemists in scaling up reactions efficiently and accurately.

Molar Mass Calculations

Molar mass calculations are critical to understanding chemical reactions and their outcomes. The molar mass is the weight of one mole of a given substance, expressed in grams per mole (g/mol). It combines the atomic masses of each atom in the molecule.

For example, the molar mass of magnesium oxide (MgO) is calculated by adding the masses of magnesium (24.31 g/mol) and oxygen (16.00 g/mol), resulting in 40.31 g/mol.

Similarly, the molar mass of magnesium hydroxide (Mg(OH)₂) is 58.33 g/mol. This involves summing the atomic masses of magnesium, two oxygen atoms, and two hydrogen atoms.

Aluminium hydroxide (Al(OH)₃) has a molar mass of 78.01 g/mol, derived from the masses of aluminium, three oxygen atoms, and three hydrogen atoms.

Knowing these molar masses is crucial, as they allow us to calculate how many moles are in a given mass and predict how much acid a certain weight of antacid can neutralize.