Question

What is a salt? Give two balanced chemical equations showing how a salt is formed when an acid reacts with a base.

Short answer

A salt is an ionic compound formed when an acid reacts with a base, in which the hydrogen ions (H+) from the acid are replaced by metal ions (or other positively charged ions) from the base. For example, the reaction between Hydrochloric acid (HCl) and Sodium Hydroxide (NaOH) produces Sodium Chloride (NaCl) and water: \[ HCl(aq) + NaOH(aq) \rightarrow NaCl(aq) + H_2O(l) \] Another example is the reaction between Sulfuric acid (H2SO4) and Magnesium Hydroxide (Mg(OH)2) which forms Magnesium Sulfate (MgSO4) and water: \[ H2SO4(aq) + Mg(OH)2(s) \rightarrow MgSO4(aq) + 2H_2O(l) \]

Step-by-step solution

Definition of a Salt

A salt is an ionic compound formed when an acid reacts with a base, and the hydrogen ions (H+) from the acid are replaced by metal ions (or other positively charged ions) from the base. The general formula for a salt is M+A-, where M is a metal (or another positively charged ion) and A is an anion.

Example 1: Formation of Sodium Chloride (NaCl)

In this example, we will consider the reaction between Hydrochloric acid (HCl) and Sodium Hydroxide (NaOH): HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) This is a balanced chemical equation since there is an equal number of atoms of each element on both sides of the equation.

Example 2: Formation of Magnesium Sulfate (MgSO4)

In this example, we will consider the reaction between Sulfuric acid (H2SO4) and Magnesium Hydroxide (Mg(OH)2): H2SO4(aq) + Mg(OH)2(s) → MgSO4(aq) + 2H2O(l) This is a balanced chemical equation since there is an equal number of atoms of each element on both sides of the equation.

Key concepts

Ionic Compounds

Ionic compounds are formed through the chemical reaction between two ions: a positively charged ion known as a cation, and a negatively charged ion known as an anion.
In a salt formation, the cation is usually a metal, and the anion comes from the decomposed acid.
These opposite charges attract each other, which leads to the formation of a stable, neutral ionic compound.

• Cations are often metals like Sodium (Na⁺) or Magnesium (Mg²⁺).
• Anions might be non-metallic ions like Chloride (Cl⁻) or Sulfate (SO₄²⁻).

When combined, these ions form a solid structure known as a crystal lattice, where ions are arranged in a repeating pattern. This structure makes salts typically hard and brittle, and many are highly soluble in water.
When dissolved, salts disassociate into their individual ions, enabling them to conduct electricity.

Acid-Base Reaction

An acid-base reaction is a fundamental chemical process that occurs when an acid and a base interact and exchange ions.
The process results in the neutralization of the acid's hydrogen ions ( H⁺ ) by the base’s hydroxide ions ( OH⁻ ), forming water ( H₂O ), and usually a salt.

• Acids are substances that can donate hydrogen ions ( H⁺ ) in a chemical reaction, like Hydrochloric acid (HCl) or Sulfuric acid ( H₂SO₄ ).
• Bases are compounds that can accept hydrogen ions, often dissociating into ions in water, such as Sodium hydroxide (NaOH) and Magnesium hydroxide ( Mg(OH)₂ ).

This exchange is an essential chemical process not just in laboratory reactions, but also in food science, pharmaceuticals, and even our own biological systems. It leads to a balanced chemical equation, as witnessed in the formation of sodium chloride ( NaCl ) or magnesium sulfate ( MgSO₄ ).

Balanced Chemical Equations

Balanced chemical equations are central to understanding chemical reactions as they depict how matter is conserved.
Each balanced equation illustrates that the number of atoms for each element involved remains constant throughout the reaction.
This balancing follows from the Law of Conservation of Mass, which states that matter cannot be created or destroyed.

• The left side of the equation (reactants) should have the same number of atoms of each type as the right side (products).
• For instance, the balanced equation: HCl + NaOH → NaCl + H₂O shows equal amounts of each element.

To achieve a balance, coefficients are adjusted, but never the subscripts in compounds, as this changes the actual substances involved.
Balancing equations ensures accuracy in representing the chemical process and allows for proper determination of reactant-product ratios.