Problem 53 - Chemistry Matter and Change

Question

Antacids Magnesium hydroxide is an ingredient in some antacids. Antacids react with excess hydrochloric acid in the stomach to relieve indigestion. \begin{equation} \underline\ \mathrm{Mg}(\mathrm{OH})_{2}+\longrightarrow \mathrm{HCl} \rightarrow \underline{} \mathrm{MgCl}_{2}+\underline{} \mathrm{H}_{2} \mathrm{O} \end{equation} \begin{equation} \begin{array}{l}{\text { a. Balance the reaction of Mg }(\mathrm{OH})_{2} \text { with HCl. }} \\ {\text { b. Write the mole ratio that would be used to determine }} \\ {\text { the number of moles of MgCl produced when HCl }} \\\ {\text { reacts with } \mathrm{Mg}(\mathrm{OH})_{2} \text { . }}\end{array} \end{equation}

Step-by-Step Solution

Answer

a) The balanced equation: \( \mathrm{Mg}(\mathrm{OH})_{2} + 2 \mathrm{HCl} \rightarrow \mathrm{MgCl}_{2} + 2 \mathrm{H}_{2}\mathrm{O} \). b) Mole ratio: 2:1 (HCl:MgCl\(_2\)).

Step 1: Write the Unbalanced Equation

The given chemical reaction is: \( \mathrm{Mg}(\mathrm{OH})_{2} + \underline{} \mathrm{HCl} \rightarrow \underline{} \mathrm{MgCl}_{2} + \underline{} \mathrm{H}_{2}\text{O} \). Right now, it is not balanced.

Step 2: Balance Magnesium and Chlorine

Mg from Mg(OH)\(_2\) reacts to form MgCl\(_2\). There is 1 Mg on each side, so they are already balanced. Chlorine on the right (MgCl\(_2\)) has 2 Cl atoms, so the left side must also have 2 Cl atoms, leading to 2 HCl: \( \mathrm{Mg}(\mathrm{OH})_{2} + 2 \mathrm{HCl} \rightarrow \mathrm{MgCl}_{2} + \mathrm{H}_{2}\mathrm{O} \).

Step 3: Balance Hydrogen and Oxygen

With 2 HCl, we have 2 H atoms from HCl. Mg(OH)\(_2\) provides 2 additional H atoms and 2 O atoms on the left, giving us 4 total H atoms (2 from HCl and 2 from 1 mole of hydroxide groups) and 2 O atoms. On the right, the 2 H\(_2\)O required must also match with the same 4 H atoms and 2 O atoms, fulfilling both the Hydrogen and Oxygen balance: \( \mathrm{Mg}(\mathrm{OH})_{2} + 2 \mathrm{HCl} \rightarrow \mathrm{MgCl}_{2} + 2 \mathrm{H}_{2}\mathrm{O} \).

Step 4: Write the Mole Ratio

The balanced reaction is \( \mathrm{Mg}(\mathrm{OH})_{2} + 2 \mathrm{HCl} \rightarrow \mathrm{MgCl}_{2} + 2 \mathrm{H}_{2}\mathrm{O} \). From this, the mole ratio of \( \mathrm{HCl} \) to \( \mathrm{MgCl}_{2} \) is 2:1.

Key Concepts

Mole Ratio

To understand chemical reactions, it's essential to grasp the concept of the mole ratio. This term describes the proportionate relationship between the elements or compounds involved in a reaction. A balanced chemical equation is crucial in deriving these ratios because it shows the quantities of reactants and products that are involved. For example, in our balanced reaction \( \mathrm{Mg}(\mathrm{OH})_{2} + 2 \mathrm{HCl} \rightarrow \mathrm{MgCl}_{2} + 2 \mathrm{H}_{2}\mathrm{O} \), the mole ratio derived from this equation for \( \mathrm{HCl} \) to \( \mathrm{MgCl}_{2} \) is 2:1. This means that 2 moles of hydrochloric acid react with 1 mole of magnesium hydroxide to form 1 mole of magnesium chloride. This ratio helps in calculating the amount of products formed or reactants consumed in a reaction.

• Mole ratios are derived from the coefficients of a balanced chemical equation.
• They provide a conversion factor between reactants and products.
• Knowing the mole ratio is essential to solve stoichiometry problems.

Chemical Reaction

A chemical reaction involves the transformation of reactants into products, through processes involving breaking and forming chemical bonds. Reactions change the chemical structure and energy states of the substances involved. In this exercise, the reaction between magnesium hydroxide and hydrochloric acid is a perfect example of a chemical change. Here, magnesium hydroxide neutralizes hydrochloric acid, forming magnesium chloride and water. Every chemical reaction adheres to the law of conservation of mass, which means the mass and number of atoms of the reactants must be equal to that of the products.

• Reactants are the starting substances, and products are the substances formed.
• Equations must be balanced to accurately reflect the conservation of mass.
• Chemical reactions involve energy changes, often in the form of heat.

Magnesium Hydroxide

Magnesium hydroxide is an important compound in chemistry, often used as an antacid or laxative due to its ability to neutralize acids. In the given exercise, magnesium hydroxide reacts with hydrochloric acid, showcasing its role in neutralization reactions. The chemical formula for magnesium hydroxide is \( \mathrm{Mg}(\mathrm{OH})_{2} \). In the stomach, it reacts with excess hydrochloric acid to form water and magnesium chloride. This reaction helps relieve symptoms of indigestion by neutralizing stomach acid.

• Formula: \( \mathrm{Mg}(\mathrm{OH})_{2} \)
• Neutralizes acids to relieve discomfort.
• Commonly used in medicine and chemistry.

Hydrochloric Acid

Hydrochloric acid is a strong, corrosive acid that plays a crucial role in various chemical reactions and industrial processes. In our stomachs, it aids digestion by breaking down food and killing bacteria. The chemical formula for hydrochloric acid is \( \mathrm{HCl} \). When used in the exercise's context, it reacts with magnesium hydroxide to produce magnesium chloride and water. This reaction is a classic example of how acids interact with bases, showcasing the broader principles of acid-neutralization reactions.

• Formula: \( \mathrm{HCl} \)
• Strong acid used in many industrial and laboratory processes.
• Vital for digestive processes in the human body.