Problem 51 - Chemistry The Central Science

Question

Magnesium ions are removed in water treatment by the addition of slaked lime, \(\mathrm{Ca}(\mathrm{OH})_{2}\). Write a balanced chemical equation to describe what occurs in this process.

Step-by-Step Solution

Answer

The balanced chemical equation for the removal of magnesium ions in water treatment by the addition of slaked lime is: \[ \mathrm{Mg}^{2+} + \mathrm{Ca}(\mathrm{OH})_{2} \rightarrow \mathrm{Mg}(\mathrm{OH})_{2} + \mathrm{Ca}^{2+} \]

Step 1: Write the unbalanced chemical equation

Write the unbalanced chemical equation for the removal of magnesium ions (Mg²⁺) in water treatment by the addition of slaked lime (Ca(OH)₂). \[ \mathrm{Mg}^{2+} + \mathrm{Ca}(\mathrm{OH})_{2} \rightarrow \]

Step 2: Identify the products of the reaction

The reaction between magnesium ions and slaked lime will produce magnesium hydroxide (Mg(OH)₂), a solid precipitate, and calcium ions (Ca²⁺): \[ \mathrm{Mg}^{2+} + \mathrm{Ca}(\mathrm{OH})_{2} \rightarrow \mathrm{Mg}(\mathrm{OH})_{2} + \mathrm{Ca}^{2+} \]

Step 3: Balance the chemical equation

To balance the chemical equation, make sure the number of atoms of each element is equal on both the reactant and product side of the equation. The unbalanced equation is \[ \mathrm{Mg}^{2+} + \mathrm{Ca}(\mathrm{OH})_{2} \rightarrow \mathrm{Mg}(\mathrm{OH})_{2} + \mathrm{Ca}^{2+} \] Looking at the equation, we have one Mg²⁺ ion, one Ca²⁺ ion, and two OH⁻ ions on both sides of the equation, so the equation is already balanced: Balanced chemical equation: \[ \mathrm{Mg}^{2+} + \mathrm{Ca}(\mathrm{OH})_{2} \rightarrow \mathrm{Mg}(\mathrm{OH})_{2} + \mathrm{Ca}^{2+} \]

Key Concepts

Chemical Reactions in Water Treatment

Ensuring that water is clean and safe for consumption is essential, and chemical reactions play a fundamental role in the treatment process.

During water treatment, various contaminants are removed, including bacteria, organic compounds, and inorganic minerals such as magnesium. The removal of magnesium ions (Mg²⁺) involves a chemical reaction where a reagent, such as slaked lime (Ca(OH)₂), is added to the water. This reaction is vital for softening water, as magnesium can cause hardness, which is undesirable for many everyday uses.

By understanding the chemistry behind water treatment, we improve the efficiency and effectiveness of the purification process, making it not only a technical endeavor but also a scientific one that hinges on precise chemical changes.

Precipitation Reaction

A precipitation reaction is a vital type of chemical reaction where soluble ions in a solution react to form insoluble compounds that precipitate out of the solution as a solid.

In our example, when slaked lime is added to water containing magnesium ions, magnesium hydroxide (Mg(OH)₂) is formed. This new compound is not soluble in water and hence precipitates out as a solid. This process can be visually observed and is a critical step in water treatment for removing certain ions, such as magnesium.

Precipitation reactions are not only important in environmental applications but are also extensively used in various industries, including pharmaceuticals and metallurgy. By identifying the insoluble compounds that form, we can predict and utilize precipitation reactions for numerous practical applications.

Stoichiometry

Stoichiometry is the part of chemistry that deals with the quantities of substances involved in reactions.

It enables us to understand the proportions in which different substances react and to predict the amounts of products formed. For a balanced chemical equation, such as the one between magnesium ions and slaked lime, stoichiometry tells us that one mole of Mg²⁺ reacts with one mole of Ca(OH)₂ to produce one mole of Mg(OH)₂ and one mole of Ca²⁺.

This stoichiometric relationship is key to designing processes with the correct amounts of reactants, ensuring that the reaction proceeds efficiently and that resources are not wasted. For students tackling chemistry problems, a strong grasp of stoichiometry is indispensable for solving quantitative exercises and understanding the fundamental principles underlying chemical reactions.