<div class="fusion-layout-column fusion_builder_column fusion-builder-column-41 fusion_builder_column_1_1 1_1 fusion-flex-column" style="--awb-bg-size:cover;--awb-width-large:100%;--awb-margin-top-large:0px;--awb-spacing-right-large:1.92%;--awb-margin-bottom-large:20px;--awb-spacing-left-large:1.92%;--awb-width-medium:100%;--awb-order-medium:0;--awb-spacing-right-medium:1.92%;--awb-spacing-left-medium:1.92%;--awb-width-small:100%;--awb-order-small:0;--awb-spacing-right-small:1.92%;--awb-spacing-left-small:1.92%;"> Salts are ionic compounds formed when an acid reacts with a base, typically producing salt and water.

More About Salts

Introduction

Salts are an important class of chemical compounds that are formed when acids react with bases. They are widely used in everyday life and industry, from table salt to chemical compounds used in construction and food preservation. Salts are ionic compounds made up of positively charged ions (cations) from a base and negatively charged ions (anions) from an acid.

Formation of Salts

Salts are typically formed in neutralization reactions, where an acid reacts with a base to form a salt and water. This reaction cancels out the acidic and basic properties of the reactants.

Neutralization Reaction:

$\boldsymbol{\textbf{Acid} + \textbf{Base} \rightarrow \textbf{Salt} + \textbf{Water}}$
- Example: When hydrochloric acid ( $\boldsymbol{\textbf{HCl}}$ ) reacts with sodium hydroxide ( $\boldsymbol{\textbf{NaOH}}$ ), they neutralize each other to form sodium chloride ( $\boldsymbol{\textbf{NaCl}}$ ) and water ( $\boldsymbol{\textbf{H}_2\textbf{O}}$ ).
- $\boldsymbol{\textbf{HCl} + \textbf{NaOH} \rightarrow \textbf{NaCl} + \textbf{H}_2\textbf{O}}$

Salts can also be formed by other types of reactions, such as:

Reaction of acids with metals (produces salt and hydrogen gas).
- Example: Zinc reacts with hydrochloric acid to form zinc chloride ( $\boldsymbol{\textbf{ZnCl}_2}$ ) and hydrogen gas.
- $\boldsymbol{\textbf{Zn} + 2\textbf{HCl} \rightarrow \textbf{ZnCl}_2 + \textbf{H}_2}$

Reaction of acids with metal carbonates (produces salt, carbon dioxide, and water).
- Example: Calcium carbonate reacts with hydrochloric acid to form calcium chloride ( $\boldsymbol{\textbf{CaCl}_2}$ ), carbon dioxide ( $\boldsymbol{\textbf{CO}_2}$ ), and water ( $\boldsymbol{\textbf{H}_2\textbf{O}}$ ).
- $\boldsymbol{\textbf{CaCO}_3 + 2\textbf{HCl} \rightarrow \textbf{CaCl}_2 + \textbf{CO}_2 + \textbf{H}_2\textbf{O}}$

Types of Salts

Normal Salts
- These salts are formed when all hydrogen ions ( $\boldsymbol{\textbf{H}^+}$ ) of an acid are replaced by metal ions or ammonium ions.
- Example: Sodium chloride ( $\boldsymbol{\textbf{NaCl}}$ ) is a normal salt formed from hydrochloric acid and sodium hydroxide.

Acidic Salts
- These salts are formed when an acid is partially neutralized by a base, and there are still replaceable hydrogen ions ( $\boldsymbol{\textbf{H}^+}$ ) in the salt.
- Example: Sodium bisulphate ( $\boldsymbol{\textbf{NaHSO}_4}$ ) is formed by the partial neutralization of sulfuric acid with sodium hydroxide.
  $\boldsymbol{\textbf{H}_2\textbf{SO}_4 + \textbf{NaOH} \rightarrow \textbf{NaHSO}_4 + \textbf{H}_2\textbf{O}}$

Basic Salts
- These salts are formed when a base is partially neutralized by an acid, and there are still hydroxide ions ( $\boldsymbol{\textbf{OH}^-}$ ) in the salt.
- Example: Zinc hydroxide chloride ( $\boldsymbol{\textbf{Zn(OH)Cl}}$ ) is a basic salt formed by the partial neutralization of zinc hydroxide with hydrochloric acid.

Double Salts
- Double salts are formed when two different salts crystallize together in a definite ratio.
- Example: Potash alum ( $\boldsymbol{\textbf{K}_2\textbf{SO}_4 \cdot \textbf{Al}_2(\textbf{SO}_4)_3 \cdot 24\textbf{H}_2\textbf{O}}$ ) is a double salt used in water purification.

Complex Salts
- Complex salts contain a metal ion bonded to multiple ligands (atoms or molecules that donate electrons to the metal ion).
- Example: Potassium ferrocyanide ( $\boldsymbol{\textbf{K}_4[\textbf{Fe(CN)}_6]}$ ) is a complex salt used in the steel industry.

Important Salts and Their Uses

Sodium Chloride ( $\boldsymbol{\textbf{NaCl}}$ ) – Common Salt
- Use: Used as table salt for seasoning food, as a preservative, and in the chemical industry to produce chlorine gas and sodium hydroxide.
- Source: Obtained from seawater or salt mines.

Sodium Bicarbonate ( $\boldsymbol{\textbf{NaHCO}_3}$ ) – Baking Soda
- Use: Used in baking to make dough rise, as an antacid to neutralize stomach acid, and as a mild cleaning agent.
- Reaction in Baking: When heated, sodium bicarbonate decomposes to release carbon dioxide gas, which causes dough to rise.
  $\boldsymbol{2\textbf{NaHCO}_3 \rightarrow \textbf{Na}_2\textbf{CO}_3 + \textbf{CO}_2 + \textbf{H}_2\textbf{O}}$

Calcium Carbonate ( $\boldsymbol{\textbf{CaCO}_3}$ )
- Use: Used in the construction industry to make cement and lime, as well as in antacid tablets to neutralize stomach acid.
- Source: Found in limestone, marble, and chalk.

Gypsum ( $\boldsymbol{\textbf{CaSO}_4 \cdot 2\textbf{H}_2\textbf{O}}$ )
- Use: Used in the manufacture of plaster of Paris ( $\displaystyle {\boldsymbol{\textbf{CaSO}_4\cdot\frac{1}{2}\textbf{H}_2\textbf{O}}}$ ), which is used for making casts and sculptures.
- Plaster of Paris Formation: $\displaystyle {\boldsymbol{\textbf{CaSO}_4 \cdot 2\textbf{H}_2\textbf{O} \xrightarrow{\textbf{Heat}} \textbf{CaSO}_4 \cdot \frac{1}{2}\textbf{H}_2\textbf{O} + \textbf{H}_2\textbf{O}}}$
- Source: Naturally occurring as gypsum rock.

Potassium Nitrate ( $\boldsymbol{\textbf{KNO}_3}$ )
- Use: Used in fertilizers and fireworks.
- Source: Extracted from the earth and synthesized in chemical processes.

Water of Crystallization

Some salts contain water molecules as part of their crystalline structure. This water is called water of crystallization, and it is essential for maintaining the structure of the salt.

Example: Copper sulfate pentahydrate ( $\boldsymbol{\textbf{CuSO}_4\cdot5\textbf{H}_2\textbf{O}}$ ) contains five molecules of water in its structure. When heated, it loses water and turns from blue to white.
$\boldsymbol{\textbf{CuSO}_4\cdot5\textbf{H}_2\textbf{O} \xrightarrow{\textbf{Heat}} \textbf{CuSO}_4 + 5\textbf{H}_2\textbf{O}}$

Salts that contain water of crystallization are referred to as hydrated salts, while those that do not are called anhydrous salts.

pH of Salts

Salts can have different pH values depending on the nature of the acid and base used to form them:

Neutral Salts: Formed from the reaction of a strong acid and a strong base. These salts have a pH close to 7.
- Example: Sodium chloride ( $\boldsymbol{\textbf{NaCl}}$ ) is a neutral salt.

Acidic Salts: Formed from the reaction of a strong acid and a weak base. These salts have a pH less than 7.
- Example: Ammonium chloride ( $\boldsymbol{\textbf{NH}_4\textbf{Cl}}$ ) is an acidic salt.

Basic Salts: Formed from the reaction of a weak acid and a strong base. These salts have a pH greater than 7.
- Example: Sodium carbonate ( $\boldsymbol{\textbf{Na}_2\textbf{CO}_3}$ ) is a basic salt.

Real-life Applications of Salts

Food Preservation:

Sodium chloride ( $\boldsymbol{\textbf{NaCl}}$ ) is widely used in the preservation of food. It prevents the growth of bacteria and other microorganisms by drawing water out of their cells through osmosis.

Fertilizers:

Ammonium nitrate ( $\boldsymbol{\textbf{NH}_4\textbf{NO}_3}}$ ) and potassium nitrate ( $\boldsymbol{\textbf{KNO}_3}}$ ) are used in agriculture as fertilizers to provide essential nutrients (nitrogen and potassium) for plant growth.

Medicine:

Sodium bicarbonate ( $\boldsymbol{\textbf{NaHCO}_3}$ ) is used in antacids to neutralize excess stomach acid, providing relief from indigestion and heartburn.
Calcium sulfate ( $\boldsymbol{\textbf{CaSO}_4}$ ) is used in plaster of Paris, which is applied to make casts for broken bones.

Water Purification:

Alum (potassium aluminum sulfate, $\boldsymbol{\textbf{KAl(SO}_4)_2}$ ) is used in water purification to remove suspended particles by coagulating them.

Industrial Uses:

Sodium carbonate ( $\boldsymbol{\textbf{Na}_2\textbf{CO}_3}$ ) is used in the manufacture of glass, soap, and paper.
Calcium chloride ( $\boldsymbol{\textbf{CaCl}_2}$ ) is used for de-icing roads and as a drying agent in laboratories.

Practice Questions with Answers

Q1. How is sodium chloride (NaCl) formed?

Answer: Sodium chloride is formed when hydrochloric acid reacts with sodium hydroxide in a neutralization reaction.
- Equation: $\boldsymbol{\textbf{HCl} + \textbf{NaOH} \rightarrow \textbf{NaCl} + \textbf{H}_2O}$

Q2. What is the difference between an acidic salt and a basic salt?

Answer: An acidic salt is formed from a strong acid and a weak base, and has a pH less than 7 (e.g., ammonium chloride, $\boldsymbol{{NH}_4C}$ ). A basic salt is formed from a weak acid and a strong base, and has a pH greater than 7 (e.g., sodium carbonate, $\boldsymbol{{Na}_2{CO}_3}$ ).

Q3. What is plaster of Paris and how is it formed?

Answer: Plaster of Paris is calcium sulphate hemihydrate ( $\boldsymbol{\textbf{CaSO}_4 \cdot \frac{1}{2}\textbf{H}_2\textbf{O}}$ ). It is formed by heating gypsum ( $\boldsymbol{\textbf{CaSO}_4 \cdot 2\textbf{H}_2\textbf{O}}$ ) to remove part of its water of crystallization.
- Equation: $\boldsymbol{\textbf{CaSO}_4 \cdot 2\textbf{H}_2\textbf{O} \xrightarrow{\text{Heat}} \textbf{CaSO}_4 \cdot \frac{1}{2}\textbf{H}_2\textbf{O} + \textbf{H}_2\textbf{O}}$
This equation represents the process where gypsum is heated to form plaster of Paris by removing water from its structure.

Q4. What is the role of alum in water purification?

Answer: Alum ( $\boldsymbol{\textbf{KAl(SO}_4)_2}$ ) is used in water purification to coagulate and remove suspended particles from the water, making it clearer.