Salt Definition

A carbon atom that contains one cation (positively charged) and one anion (negatively charged) is known as salt. Salt is an essential component found in seawater in large quantities. Salts are naturally occurring solid compounds available in their pure form. It can be categorized as an ionic compound because it has a cation of acid and an anion of the base.

Salts are the products of the neutralized reaction between acids and bases. The ionic bonding between sodium and chloride ions leads to the formation of Sodium chloride salt. The term 'salt' is most commonly known for the chemical compound sodium chloride (NaCl), representing a 1:1 ratio of sodium and chloride ions.

Properties of Salts

Salt usually consists of OH- and H+ ions that are attracted to each other because they are oppositely charged ions and have an electrostatic attraction force between them.

Saltwater is a superconductor of electricity because sodium chloride ions are separated into charged sodium and chloride ions. These ions are as free to move in water as positively and negatively charged ions.
Salts have an equal number of positively and negatively charged ions. Therefore, salts are neutral compounds with no charge.
Salts are brittle and crystalline solids in an isometric system.
All salts, such as potassium, ammonium, and calcium, are soluble in water. It is because both salt compounds and water are polar in nature. Also, the electrical charges are located on opposite sides of the molecule.
The salts that are purely composed of sodium and chloride are typically white in color because there are no other elements present in them.
Salts are odorless and salty because they are nonvolatile.
Salts show no chemical reaction with oxygen. Therefore, they are non-combustible and have low toxicity.

Note- It is a dangerous substance that must be stored in cold surroundings. If it comes in contact with acidic substances, it can produce toxic fumes of chlorine.

Origin of Salt (NaCl)

Around 600 BC, the first salt harvesting took place at Lake Yuncheng, located in China.
According to historical accounts, salt (NaCl) was first discovered by the North Americans around 500 years before the arrival of colonizers, and it was extracted from the Salt Valley.
In 1812, it was produced by the boiling of brine water when the wars were taking place.
Salt has been produced in India from the Rann of Kutch for the last 5000 years.

Types of Salts

Salts are categorized into five major types, such as:

1. Acidic Salts

The salts that are formed by the neutralization of strong acid and a weak base are known as acidic salt. In other words, salts that are produced through the partial neutralization of polybasic (compounds that donate more than one proton per acidic molecule) are acidic salts. During the formation of acidic salts, H+ ions that mostly act as an anion are iodized with another cation. An example of acidic salt is ammonium chloride (NH?Cl), which is produced through the neutralization reaction (given below) between aqueous ammonia and hydrogen chloride (a strong acid).

NH3 + HCl -> NH4Cl

2. Alkali Salts

The salts that are produced by the incomplete reaction between a strong base and a weak acid are known as alkali salts. In this reaction, the hydrolysis of the basic solution produces the salt. These salts are not neutral in nature and show basic properties. Alkali salts are beneficial for purposes such as industrial cleaning and preserving food items. Examples of alkali salts are potassium hydroxide and sodium hydroxide.

3. Double Salt

The salts composed of more than one anion or cation are known as double salts. These salts are formed by the mixing of two salts that are crystallized in the common regular ionic lattice. An example of double salt is Mohr's salt, also known as ammonium iron (II) sulfate, which is comprised of ammonium sulfate and ferrous sulfate. It is used as a laboratory reagent that helps form crystals. Other instances of double salts are potash alum, alstonite, carnallite, and dolomite.

4. Mixed Salt

The salts that are constituted of a fixed proportion of salts and mostly share an anion or a cation with one another are known as mixed salts. These salts contain more than one basic radical or acidic radical. The crystallization of mixed slats is a slow process and produces a mixture of a saturated solution. Mixed salts are usually available in the form of cubes, and these are used for treating ADHD (Attention-deficit/hyperactivity disorder) patients.

5. Complex Salts

A compound that is comprised of a central metal atom that forms coordination bonds with ligands surrounding it is known as complex salt. The cations and anions in these compounds bond with each other forming a complex structure. The saturated solutions of two different salts are mixed with each other before the final solution gets crystallized to produce mixed salts. Examples of complex salt solids are sodium potassium ferrocyanide and potassium argentocyanide.

Hydrolysis of Salts

When the salt is formed as an ionic compound, the acidic and alkaline radicals neutralize each other. The solution that is formed as a product seems like it is neutral. However, in most cases, they are either acidic or basic in character. A reaction in which an ion that is present in salt reacts with water to produce an acidic or basic solution as a product is known as salt hydrolysis. It is the reverse reaction of the neutralization process.

Hydrolysis of Weak Acids and Strong Bases

When a weak acid such as hydrofluoric acid is combined with a strong base such as sodium hydroxide, a salt called sodium fluoride is produced along with water. In the neutralization reaction, sodium ion acts as a spectator ion because sodium fluoride is soluble in water. The fluoride ion that functions as a weak base reacts with water and accepts a proton. The hydroxide ion is produced as a product of this reaction, and therefore, the solution that is produced at last is basic in nature.

Hydrolysis of Strong Acids and Strong Bases

The salts that are formed by the neutralized reaction between a strong acid and a strong base are of neutral character because, in the salt solution, bonds cannot be broken. Acidic salts mostly absorb water but do not get hydrolyzed. Hence, these salts are characterized as neutral salts.

For example- Sodium chloride is the product of a strong acid (HCl) and a strong base (NaOH) neutralization reaction. Hence, it is neutral in nature. For hydrolysis to take place, one of the reactants or both reactants should be weak. Therefore, sodium chloride, which is a neutral salt, does not undergo hydrolysis and doesn't show any reaction with water.

Hydrolysis of a Weak Acid and Weak Base

Salts that are formed by the combination of weak acids and weak bases can be acidic, basic, or neutral based on the reactants used in their formation. After hydrolysis, if the dissociation constant of one product is higher than the dissociation constant of another, the final solution might show the properties of the one that is stronger in nature (acidic or basic).

Examples

1. Hydrolysis of salt formed by combining weak acid with the weak base when the end product is basic due to its higher dissociation.

Let's take the hydrolysis of ammonium cyanide (NH4CN) as an example:

NH4 + CN- + H2O -> NH4OH + HCN

The dissociation constant of HCN (weak acid) is less than that of NH4OH (a weak base). Hence, the solution would show the properties of a base than an acid after hydrolysis.

2. Hydrolysis of salt formed through weak acid and weak base when the end product is more acidic than basic.

In this case, let's take the hydrolysis of ammonium fluoride (NH4F) as an example:

NH4 + F- + H2O -> NH4OH + HF

The dissociation constant of acidic HF (7.2 x 10-4) is greater than that of a basic NH4OH (1.8 x 10-5). Therefore, the solution shows the properties of acid rather than the base.

3. Hydrolysis of salt formed by combining weak base and weak acid with the same dissociation energy.

In this case, hydrolysis of ammonium acetate will display the required results.

CH3COO- + NH4+ + H2O -> CH3COOH + NH4OH

The dissociation constants of aqueous CH3COOH and NH4OH are almost equal. Therefore, the solution obtained after the hydrolysis would show a neutral character.

Hydrolysis of Weak Bases with Strong Acids

After the neutralization of the weak base with strong acid, the solution shows acidic properties. For example- NH4Cl is formed by the combination of NH3 (a weak base) and HCl (strong acid). Ammonia accepts a proton from other hydrogen atoms and partially dissociates in water. Therefore, an acidic solution is yielded as a product.

NH4Cl -> Cl- + NH4+

Hydrolysis of NH4+ ion

NH4+ + H2O -> NH4OH + H+

Ammonium hydroxide and hydrogen ions are formed when ammonium ions undergo hydrolysis. Ammonium hydroxide is a weak base. Therefore, it does not get ionized. On the other hand, due to the high concentration of H+ ions, the solution would show an acidic character. However, its pH would be less than 7.

Uses of Salts

Salts are used for many purposes due to their properties. Some of the major salts, their properties, and their uses are mentioned below:

1. Sodium Carbonate (Na2CO3. 10H2O)

Uses

This salt is commonly known as washing soda.
It is available in the form of monohydrated salts.
It is of greyish white color and odorless.

It acts as a cleansing agent.
The permanent hardness of water is removed by using washing soda.
Washing soda is used for glass, soap, and industrial paper.

2. Sodium Bicarbonate (NaHCO3)

This salt is commonly known as baking soda.
It is in the form of a white crystalline solid.
It does not get dissolved in ethanol.
In a monoclinic crystal lattice, the sodium bicarbonate forms crystals.

Uses

It is used for cooking and baking.
It is used as a pest-controlling substance.
It is used to clean teeth and the mouth.
It is used to prepare fire extinguishers.

3. Sodium Chloride (NaCl)

The common name of sodium chloride is table salt.
It can get easily dissolved in water and acts as partially soluble or insoluble in other liquids.
When it is mixed in liquid, electrolysis can take place, and electricity can pass through salt water easily.
It is obtained through the evaporation of seawater in the form of crystals.

Uses

It is used by many food companies as a food preservative and increases the flavor of food.
It is used to melt the snow on the roads to avoid roadblocks in the winter season in countries with cold climates.
It is used in the manufacturing of glass.
It is used in the industrial production of other salts, such as washing and baking soda.
It is used by soap manufacturing industries.

4. Hemihydrate Calcium Sulphate (CaSO4. ½ H2O)

Although it is basic salt, it is generally known as the Plaster of Paris.
It is the dehydrated form of gypsum (CaSO4.2H2O).
It shows an exothermic reaction with water and moist air and hardens to form gypsum.
It decomposes in surroundings with high temperatures and produces toxic sulfur oxides.
It is a non-combustible compound.

Uses

A protective coating of POP is applied on walls and ceilings for quick finishing.
It is used as a fire-resistant material to prevent buildings and houses from burning.
It is used in hospitals in the form of casts that provide support to broken bones so that they can heal properly. The hardened casts give shape and support to fractured bones.
The molds for the replacement of teeth are prepared by using POP.

5. Calcium Chloride (CaCl2)

It is an acidic salt that is acquired from natural brines.
It is produced through the reaction between hydrochloric acid and limestone.
It is a strong electrolyte.
It participates in exothermic reactions when combined with water and produces heat.

Uses

It is used to keep the tissues of canned vegetables and fruits firm and crispy.
It is used as an electrolyte in energy drinks and packaged water.
It is used for dust control while making roads and de-icing them (as it acts as de-icing agent).
It is used in wastewater treatment plants to get rid of impurities in water.

6. Calcium hypochlorite [Ca (ClO)2]

It is commonly called Bleaching powder, and it is a neutral compound.
It is a powerful oxidizing agent, and in reaction with water, it produces heat, chlorine, and oxygen gases.
At room temperature, it is a white and grey solid substance.
It decomposes slowly in a moist environment, giving off a characteristic 'chlorine' odor.
It is partially insoluble in hard water.

Uses