Problem 81 - Chemistry

Question

Metal chlorides can be prepared in a number of ways: (a) direct combination of metal and molecular chlorine, (b) reaction between metal and hydrochloric acid, (c) acid-base neutralization, (d) metal carbonate treated with hydrochloric acid, (e) precipitation reaction. Give an example for each type of preparation.

Step-by-Step Solution

Answer

Direct Combination: \(2Na + Cl_{2} \rightarrow 2NaCl\), Reaction with Acid: \(Mg + 2HCl \rightarrow MgCl_{2} + H_{2}\), Acid-Base Neutralization: \(NaOH + HCl \rightarrow NaCl + H_{2}O\), Treated Metal Carbonate with acid: \(CaCO_{3} + 2HCl \rightarrow CaCl_{2} + CO_{2} + H_{2}O\), Precipitation Reaction: \(AgNO_{3} + NaCl \rightarrow AgCl + NaNO_{3}\).

Step 1: Direct Combination

A direct combination example could be the reaction between sodium (Na) and chlorine (Cl) to form sodium chloride (NaCl). The balanced equation for this reaction would be: \(2Na + Cl_{2} \rightarrow 2NaCl\)

Step 2: Reaction with Acid

A reaction between a metal and hydrochloric acid could be the reaction between magnesium (Mg) and hydrochloric acid (HCl) to form magnesium chloride (MgCl2) and hydrogen (H2). The balanced equation for this reaction is: \(Mg + 2HCl \rightarrow MgCl_{2} + H_{2}\)

Step 3: Acid-Base Neutralization

An example of acid-base neutralization could be the reaction between sodium hydroxide (NaOH) and hydrochloric acid (HCl) to form sodium chloride (NaCl) and water (H2O). The balanced equation would be: \(NaOH + HCl \rightarrow NaCl + H_{2}O\)

Step 4: Metal Carbonate Treated with Hydrochloric Acid

An example of treating a metal carbonate with hydrochloric acid could be the reaction between calcium carbonate (CaCO3) and hydrochloric acid (HCl) to form calcium chloride (CaCl2), carbon dioxide (CO2), and water (H2O). The balanced equation for this reaction would be: \(CaCO_{3} + 2HCl \rightarrow CaCl_{2} + CO_{2} + H_{2}O\)

Step 5: Precipitation Reaction

An example of a precipitation reaction could be mixing solutions of silver nitrate (AgNO3) and sodium chloride (NaCl) to form a precipitate of silver chloride (AgCl) and a solution of sodium nitrate (NaNO3). The balanced equation for this reaction is: \(AgNO_{3} + NaCl \rightarrow AgCl + NaNO_{3}\).

Key Concepts

Direct Combination Reaction

Sometimes called a synthesis reaction, the direct combination reaction involves two or more substances, usually a metal and a non-metal, interacting to form a new compound. A straightforward example of this is when sodium (\textbf{Na}) combines with chlorine (\textbf{Cl}\(_2\)) gas. These react under the right conditions to form sodium chloride (\textbf{NaCl}), commonly known as table salt, according to the equation:
\[2Na + Cl_{2} \rightarrow 2NaCl\]
In this type of reaction, the simplicity of the products—a single compound from elemental reactants—makes it easy to identify. The formation of sodium chloride showcases this concept perfectly, where the highly reactive metal sodium bonds with the non-metal chlorine, resulting in a more stable ionic compound.

Reaction Between Metal and Acid

This process illustrates how a metal reacts with an acid to produce a salt and hydrogen gas. For instance, when magnesium (\textbf{Mg}) reacts with hydrochloric acid (\textbf{HCl}), magnesium chloride (\textbf{MgCl}\(_2\)) is formed alongside the release of hydrogen gas (\textbf{H}\(_2\)). This can be represented as:
\[Mg + 2HCl \rightarrow MgCl_{2} + H_{2}\]
During this reaction, we observe that magnesium replaces hydrogen in hydrochloric acid, demonstrating the reactivity of metals. This type of reaction also provides a practical method for producing salts, such as metal chlorides.

Acid-Base Neutralization Reaction

Neutralization is a particular chemical reaction where an acid and a base interact to form a salt and water, essentially 'neutralizing' each other. An everyday example happens when sodium hydroxide (\textbf{NaOH}), a base, reacts with hydrochloric acid (\textbf{HCl}), an acid. They combine to yield sodium chloride (\textbf{NaCl}) and water (\textbf{H}\(_2\)\textbf{O}), as shown in this balanced equation:
\[NaOH + HCl \rightarrow NaCl + H_{2}O\]
Sodium chloride, the salt formed, is the same compound produced in a direct combination reaction, but the process to achieve it is markedly different. This neutralization reaction is fundamental to understanding acid-base chemistry and has various applications, from industrial processes to medicine.

Treatment of Metal Carbonate with Acid

When a metal carbonate reacts with hydrochloric acid, a metal chloride, carbon dioxide, and water are produced. A prime example is when calcium carbonate (\textbf{CaCO}\(_3\)), which is a common component of seashells and limestone, interacts with hydrochloric acid (\textbf{HCl}). This reaction is essential in geology and environmental science, often being responsible for the erosion of carbonate rocks. The reaction looks like this:
\[CaCO_{3} + 2HCl \rightarrow CaCl_{2} + CO_{2} + H_{2}O\]
The evolution of carbon dioxide is a visual indicator of this chemical response. Such reactions also have industrial significance, like in the treatment of waste or the manufacturing of building materials.

Precipitation Reaction

The precipitation reaction is a type of chemical process where two solutions, containing dissolved ions, react and form an insoluble ionic compound that precipitates out of the solution. A classic demonstration is when silver nitrate (\textbf{AgNO}\(_3\)) solution mixes with sodium chloride (\textbf{NaCl}) solution. The reaction yields a solid precipitate of silver chloride (\textbf{AgCl}) and soluble sodium nitrate (\textbf{NaNO}\(_3\)) remains in solution, as per the balanced chemical equation:
\[AgNO_{3} + NaCl \rightarrow AgCl + NaNO_{3}\]
This reaction is crucial for understanding ionic interactions in aqueous solutions and is widely used in qualitative analysis and in purifying water to remove undesired ions.