Question

Antacids Magnesium hydroxide is an ingredient in some antacids. Antacids react with excess hydrochloric acid in the stomach to relieve indigestion. ___ $\mathrm{Mg}(\mathrm{OH}{)}_2+$ ___ $\mathrm{HCl}\to$ ___ ${\mathrm{MgCl}}_2+$ ___ ${\mathrm{H}}_2\mathrm{O}$ a. Balance the reaction of $\mathrm{Mg}(\mathrm{OH}{)}_2$ with $\mathrm{HCl}$ . b. Write the mole ratio that would be used to determine the number of moles of MgCl_ produced when HCl reacts with $\mathrm{Mg}(\mathrm{OH}{)}_2$

Short answer

a. The balanced chemical equation is: $Mg(OH{)}_2+2HCl\to MgC{l}_2+2H_{2}O$ b. The mole ratio for determining the number of moles of $MgC{l}_2$ produced when $HCl$ reacts with $Mg(OH{)}_2$ is: $1moleMg(OH{)}_2:2molesHCl:1moleMgC{l}_2:2moles{H}_{2}O$

Step-by-step solution

Balancing the Chemical Equation

Let's first write down the unbalanced chemical equation given: Mg(OH)₂ + HCl → MgCl₂ + H₂O Now, we will balance the equation by adjusting the coefficients of the reactants and products while conserving the number of atoms for each element. First, note that there are 2 hydroxides (OH⁻) in the magnesium hydroxide formula, so we need 2 HCl molecules to provide 2 H⁺ ions to react with the 2 OH⁻ ions in Mg(OH)₂. This balances the hydrogen (H) and chlorine (Cl) atoms: Mg(OH)₂ + 2HCl → MgCl₂ + H₂O Finally, we need to balance the oxygen (O) atoms. Since we already have two O atoms from Mg(OH)₂ on the left side, we need 2 H₂O molecules on the right side to balance the oxygen atoms: Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O Now, the chemical equation is balanced.

Writing the Mole Ratio

To find the mole ratio that would be used to determine the number of moles of MgCl₂ produced when HCl reacts with Mg(OH)₂, we need to compare the coefficients of the reactants and products in the balanced chemical equation: Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O From the balanced equation, we can see that: - 1 mole of Mg(OH)₂ reacts with 2 moles of HCl to produce - 1 mole of MgCl₂ and 2 moles of H₂O. The mole ratio for determining the number of moles of MgCl₂ produced when HCl reacts with Mg(OH)₂ is thus: 1 mole Mg(OH)₂ : 2 moles HCl : 1 mole MgCl₂ : 2 moles H₂O So, for every 1 mole of Mg(OH)₂ reacting, 1 mole of MgCl₂ is produced.

Key concepts

Stoichiometry

Stoichiometry is at the heart of chemical reactions. It is the area of chemistry that pertains to the quantitative relationships between the substances as they participate in various chemical reactions. When we speak of stoichiometry, we refer to the calculation of reactants (the starting materials) and products (the substances formed) in a chemical reaction.

To delve into the basics, stoichiometry is grounded on the law of conservation of mass, which states that matter is neither created nor destroyed during a chemical reaction. This means that the mass of the reactants must equal the mass of the products. Stoichiometry uses the mole concept (which represents a count of 6.022×10²³ particles of a substance) to facilitate these calculations, since masses at the atomic and molecular levels are inconveniently small and impractical to measure directly.

In practice, stoichiometry involves related calculations such as determining the amounts of reactants needed to produce a certain amount of product, or the expected yield of a product given specific quantities of reactants. It enables chemists to make predictions about the outcomes of chemical reactions and ensures the efficient use of reactants.

Mole Ratio

The mole ratio is a key concept tied to stoichiometry and is derived from a balanced chemical equation. It is the proportion of moles of one substance to the moles of another substance involved in a chemical reaction.

When balancing a chemical equation, the coefficients provide the mole ratios for the reactants and products. These ratios are essential for calculations involving chemical reactions, as they tell us how much of one substance reacts with or is produced from a certain amount of another substance. To illustrate, consider the balanced equation of the reaction between magnesium hydroxide and hydrochloric acid to form magnesium chloride and water:

$$Mg(OH{)}_2+2HCl\to MgC{l}_2+2H_{2}O$$
The coefficients of the balanced chemical equation become the mole ratios, indicating that 1 mole of $Mg(OH{)}_2$ reacts with 2 moles of $HCl$ to produce 1 mole of $MgC{l}_2$ and 2 moles of $H_{2}O$. Thus, a 1:2:1:2 ratio is established between $Mg(OH{)}_2$, $HCl$, $MgC{l}_2$, and $H_{2}O$, respectively. Understanding mole ratios is vital for converting between moles of different substances in a chemical reaction.

Acid-Base Reactions

Acid-base reactions are a type of chemical reaction that occur between an acid and a base. In the context of our exercise, hydrochloric acid ($HCl$) reacts with magnesium hydroxide ($Mg(OH{)}_2$), which is a base, in a classic acid-base reaction to relieve indigestion.

This particular type of reaction is called neutralization, where an acid and a base react to form a salt—in this case, magnesium chloride ($MgC{l}_2$)—and water ($H_{2}O$). Neutralization reactions follow the general formula: $$\text{Acid}+\text{Base}\to \text{Salt}+\text{Water}$$
An essential feature of acid-base reactions is that they tend to proceed to completion, meaning that the reactants are fully consumed to form the products. This is beneficial when trying to calculate the quantities involved because if we know the amount of one reactant, we can predict the amount of product formed using stoichiometry and mole ratios.

In our example, the reaction produces a salt that is soluble in water, and this is a common outcome for reactions involving hydrochloric acid and various bases. The balanced chemical equation for any acid-base reaction is crucial because it provides the stoichiometric coefficients that lead to correct mole ratios, allowing us to perform calculations such as determining the dosage of an antacid medication.