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.

Short answer

Examples: (a) Na + Cl₂ → NaCl, (b) Mg + 2HCl → MgCl₂, (c) HCl + NaOH → NaCl + H₂O, (d) CaCO₃ + 2HCl → CaCl₂ + CO₂ + H₂O, (e) AgNO₃ + NaCl → AgCl↓ + NaNO₃.

Step-by-step solution

Direct Combination

In a direct combination reaction, a metal reacts with molecular chlorine gas to form a metal chloride. For example, sodium reacting with chlorine gas.Example Reaction: \[ 2\text{Na} + \text{Cl}_2 \rightarrow 2\text{NaCl} \] This reaction forms sodium chloride (NaCl).

Reaction with Hydrochloric Acid

A metal can react with hydrochloric acid to produce a metal chloride and hydrogen gas. For example, magnesium reacting with hydrochloric acid.Example Reaction:\[ \text{Mg} + 2\text{HCl} \rightarrow \text{MgCl}_2 + \text{H}_2 \] This reaction forms magnesium chloride (MgCl₂).

Acid-Base Neutralization

An acid-base neutralization involves an acid and a base reacting to form a salt and water. For example, hydrochloric acid reacting with sodium hydroxide.Example Reaction:\[ \text{HCl} + \text{NaOH} \rightarrow \text{NaCl} + \text{H}_2\text{O} \] This reaction forms sodium chloride (NaCl).

Metal Carbonate with Hydrochloric Acid

When a metal carbonate reacts with hydrochloric acid, it produces a metal chloride, carbon dioxide, and water. For example, calcium carbonate reacting with hydrochloric acid.Example Reaction:\[ \text{CaCO}_3 + 2\text{HCl} \rightarrow \text{CaCl}_2 + \text{CO}_2 + \text{H}_2\text{O} \] This reaction forms calcium chloride (CaCl₂).

Precipitation Reaction

In a precipitation reaction, two aqueous solutions react to form an insoluble solid (precipitate) and a solution. For example, mixing silver nitrate solution with sodium chloride solution.Example Reaction:\[ \text{AgNO}_3 + \text{NaCl} \rightarrow \text{AgCl} \downarrow + \text{NaNO}_3 \] This reaction forms silver chloride (AgCl) as a precipitate.

Key concepts

Direct Combination Reaction

Direct combination, also known as synthesis, is one of the simplest ways to prepare metal chlorides. In this method, a metal reacts directly with chlorine gas. This type of reaction involves combining two or more reactants to form a single product, often quite exothermic. A classic example is the reaction of sodium (Na) with chlorine gas (Cl_2) to produce sodium chloride (NaCl).
When sodium and chlorine react, they form sodium chloride as a result of the transfer of electrons from sodium to chlorine. The reaction can be represented by the equation: \[2\text{Na} + \text{Cl}_2 \rightarrow 2\text{NaCl}\]
This process highlights the tendency of reactive metals like sodium to form stable ionic compounds with nonmetals like chlorine.

Reaction with Hydrochloric Acid

The reaction of metals with hydrochloric acid (HCl) is another common method to prepare metal chlorides. This reaction typically results in the formation of a metal chloride and the evolution of hydrogen gas. For example, magnesium (Mg) reacts with hydrochloric acid to form magnesium chloride (MgCl_2) and hydrogen gas.
The general equation for this type of reaction is:\[\text{Metal} + 2\text{HCl} \rightarrow \text{Metal chloride} + \text{H}_2\]
Taking magnesium as an example, the reaction can be shown as:\[\text{Mg} + 2\text{HCl} \rightarrow \text{MgCl}_2 + \text{H}_2\]
This shows how reactive metals can displace hydrogen from acids to form salts like metal chlorides.

Acid-Base Neutralization

In an acid-base neutralization, an acid and a base chemically react to form a salt and water. This is an example of a double displacement reaction where the cations and anions of the reactants switch places to form new compounds. A simple and familiar reaction is between hydrochloric acid (HCl) and sodium hydroxide (NaOH), producing sodium chloride (NaCl) and water.
The reaction can be written as:\[\text{HCl} + \text{NaOH} \rightarrow \text{NaCl} + \text{H}_2\text{O}\]
This process exemplifies how an acid-base reaction can result in the formation of neutral products - a salt (sodium chloride in this case) and water. Such reactions are fundamental to various fields, including chemistry and biology.

Metal Carbonate Reaction

When a metal carbonate reacts with hydrochloric acid, the reaction results in the formation of a metal chloride, along with the release of carbon dioxide (CO_2) and water (H_2O). Calcium carbonate (CaCO_3) is a common example used in such reactions, often resulting in effervescence due to CO_2 evolution.
The general reaction can be expressed as:\[\text{Metal carbonate} + \text{HCl} \rightarrow \text{Metal chloride} + \text{CO}_2 + \text{H}_2\text{O}\]
For instance, with calcium carbonate and hydrochloric acid, the balanced equation becomes:\[\text{CaCO}_3 + 2\text{HCl} \rightarrow \text{CaCl}_2 + \text{CO}_2 + \text{H}_2\text{O}\]
This process is a key reaction in fields such as geology and environmental science, highlighting the interaction between acid rain and carbonate rocks.

Precipitation Reaction

In a precipitation reaction, two solutions combine to form an insoluble solid, or precipitate, along with another solution. The solid forms when the product is insoluble in water. A typical example is the reaction between silver nitrate (AgNO_3) and sodium chloride (NaCl) solutions, forming silver chloride (AgCl) as a precipitate.
The reaction can be written as:\[\text{AgNO}_3 + \text{NaCl} \rightarrow \text{AgCl} \downarrow + \text{NaNO}_3\]
The down arrow next to AgCl indicates the formation of a precipitate. This reaction showcases how ionic compounds dissolve to form an aqueous solution and then recombine to form an insoluble product. This type of reaction is fundamental in analytical chemistry for the qualitative analysis of ions.