What salt is formed when acid reacts with metal hydroxide?

Short Answer

When an acid reacts with a metal hydroxide, the salt formed depends on the type of acid and metal hydroxide used. In general, the reaction produces salt and water. For example, when hydrochloric acid reacts with sodium hydroxide, the salt formed is sodium chloride (NaCl).
The general reaction is:
Acid + Metal Hydroxide → Salt + Water

This reaction is a type of neutralization, where the acid’s hydrogen ions combine with the hydroxide ions to form water, and the remaining ions form the salt.

Detailed Explanation :

Salt Formed When Acid Reacts with Metal Hydroxide

A reaction between an acid and a metal hydroxide is a classic example of a neutralization reaction, where the acidic and basic properties of the reactants are cancelled out. Metal hydroxides are bases that contain hydroxide ions (OH⁻), while acids provide hydrogen ions (H⁺). When these ions react, they form water. The metal ion from the hydroxide then combines with the remaining part of the acid to form a salt.

The type of salt formed depends entirely on the combination of acid and metal hydroxide used. Understanding this reaction is important in chemistry because it explains many processes in laboratories, industry, environmental science, and daily life.

General Reaction Between Acid and Metal Hydroxide

The chemical reaction can be written as:

Acid + Metal Hydroxide → Salt + Water

This follows the neutralization pattern:

  • H⁺ (from acid) + OH⁻ (from metal hydroxide) → H₂O (water)
  • Remaining ions → form the salt

This simple but powerful concept explains how different salts are produced from different reactants.

Example Reactions and Their Salts

To understand the salt formation better, consider the following examples:

  1. Reaction of Hydrochloric Acid (HCl) with Sodium Hydroxide (NaOH)

HCl + NaOH → NaCl + H₂O

Salt formed: Sodium chloride (NaCl)
This is common table salt. The sodium ion (Na⁺) comes from sodium hydroxide, and the chloride ion (Cl⁻) comes from hydrochloric acid.

  1. Reaction of Sulphuric Acid (H₂SO₄) with Potassium Hydroxide (KOH)

H₂SO₄ + 2KOH → K₂SO₄ + 2H₂O

Salt formed: Potassium sulphate (K₂SO₄)
Here, the sulphate ion from sulphuric acid combines with potassium ions from potassium hydroxide.

  1. Reaction of Nitric Acid (HNO₃) with Calcium Hydroxide (Ca(OH)₂)

2HNO₃ + Ca(OH)₂ → Ca(NO₃)₂ + 2H₂O

Salt formed: Calcium nitrate (Ca(NO₃)₂)

  1. Reaction of Acetic Acid (CH₃COOH) with Sodium Hydroxide (NaOH)

CH₃COOH + NaOH → CH₃COONa + H₂O

Salt formed: Sodium acetate (CH₃COONa)

This example shows that organic acids also form salts during neutralization.

How Salt Formation Occurs

Salt formation during the reaction can be explained step by step:

  1. Dissociation of Acid

Acid breaks into hydrogen ions and its anion.
Example:
HCl → H⁺ + Cl⁻

  1. Dissociation of Metal Hydroxide

Metal hydroxide releases metal ions and hydroxide ions.
Example:
NaOH → Na⁺ + OH⁻

  1. Combination of H⁺ and OH⁻

These ions react to form water:
H⁺ + OH⁻ → H₂O

  1. Formation of Salt

Remaining ions combine:
Na⁺ + Cl⁻ → NaCl

This process is the same for all acid–metal hydroxide reactions.

Why Metal Hydroxides Act as Bases

Metal hydroxides contain OH⁻ ions, which neutralize hydrogen ions (H⁺). Because of this, they behave as bases according to the Arrhenius theory. They reduce acidity when mixed with acids, leading to salt formation.

Common metal hydroxides include:

  • Sodium hydroxide (NaOH)
  • Potassium hydroxide (KOH)
  • Calcium hydroxide (Ca(OH)₂)
  • Magnesium hydroxide (Mg(OH)₂)

Each produces a different salt depending on the acid used.

Importance of Salt Formation in Daily Life and Industry

Neutralization reactions between acids and metal hydroxides are used widely in:

  1. Medicine

Antacids contain metal hydroxides (like Mg(OH)₂) to neutralize stomach acid.

  1. Agriculture

Soil acidity is treated with bases that react with acidic components to form neutral salts.

  1. Water Treatment

Acidic industrial waste is neutralized using metal hydroxides.

  1. Chemical Manufacturing

Salts like sodium chloride, potassium nitrate, and calcium sulphate are produced through acid–base reactions.

  1. Food Industry

Some salts produced by neutralization are used in food preservation and flavouring.

These applications show the importance of salt formation through neutralization.

Factors Affecting the Salt Formed

The nature of the salt depends on:

  • Type of acid (hydrochloric, nitric, sulphuric, acetic, etc.)
  • Type of metal hydroxide (NaOH, KOH, Ca(OH)₂, etc.)
  • Number of hydrogen ions the acid can donate
  • Number of hydroxide ions the base can provide

For example, sulphuric acid forms salts with different metal hydroxides depending on the number of hydroxide ions available.

Conclusion

When an acid reacts with a metal hydroxide, the products are always salt and water. The exact salt depends on the specific acid and metal hydroxide involved. This reaction is an important type of neutralization and is widely used in laboratories, industries, agriculture, medicine, and household applications. Understanding this reaction helps us learn how different salts are formed and why neutralization is useful in so many fields.