Salts: Types, Preparation, Properties, Uses of Salts

Generally, Salts are formed when acids react with a base in the neutralization reaction. In salt formation, the positive part of the salt comes from the base, so it is called a basic radical, whereas the negative part comes from the acid and is called acid radical. A large number of reactions take place, forming salts.

The term “salt” is derived from the Latin word “sal,” which means “salt.” It was formerly a precious commodity that was utilised as a trading currency. The term “salary” is derived from the word “salt.” Salt has been used for seasoning and preserving food for centuries. It’s also used in tanning, dyeing, and bleaching, as well as ceramics, soap, and chlorine manufacture. In today’s chemical industry, it is widely used.

In this article, let’s learn everything about Salts in detail. Continue reading to know more.

Definition of Salts

Neutralisation reactions involving the complete or partial neutralisation of an acid by a base give rise to salt formation.

Salt is an electrovalent or ionic compound formed by the partial or complete replacement of the replaceable (ionisable) hydrogen atoms (i.e.,\({{\rm{H}}^ + }\) ions) of an acid by a metallic ion or ammonium ion. All salts are ionic in nature and strong electrolytes, i.e. they ionise completely on dissolution in water. Examples are, \({\rm{N}}{{\rm{H}}_4}{\rm{Cl,KCl,}}\,{\rm{N}}{{\rm{a}}_2}{\rm{S}}{{\rm{O}}_4}{\rm{Cl,}}\) etc.

Salts are regarded as compounds made up of positive and negative ions. The positive part comes from a base, while the negative part comes from an acid. Salts may taste salty, sour, bitter, astringent, sweet or tasteless. Solutions of salts may be acidic, basic or neutral.

(i) Hydrochloric acid \(({\rm{HCl}})\) being monobasic acid with only one replaceable (ionisable) hydrogen atom, reacts with an alkali to give a salt.
\({\rm{HCl}}\,{\rm{ + }}\,{\rm{NaOH}}\, \to {\rm{NaCl}}\,{\rm{ + }}\,{{\rm{H}}_2}{\rm{O}}\)

(ii) Sulphuric acid is a dibasic acid having two replaceable hydrogen atoms that react with alkalis, either showing partial or complete replacement of H-atoms forming two series of salts.
\({{\rm{H}}_2}{\rm{S}}{{\rm{O}}_4}\,{\rm{ + 2}}\,{\rm{NaOH}}\, \to {\rm{N}}{{\rm{a}}_2}{\rm{S}}{{\rm{O}}_4}\,{\rm{ + }}\,2{{\rm{H}}_2}{\rm{O}}\)

Classification of Salts

The salts are classified into different families based on the acids or based on the bases from which they are formed. For example, sodium chloride salt. Since it is obtained from \({\rm{Cl}}\) of \({\rm{HCl}}\) acid, it is called sodium chloride. Similarly,

1. The salts of acetic acid are called acetates,
2. The salts of carbonic acid are called carbonates,
3. The salts of nitric acid are called nitrates,
4. The salts of hydrochloric acids are called chlorides, and
5. The salts of sulphuric acid are called sulphates.

Types of Salts

The different types of salts are basic salt, normal salt, acidic salt, mixed salt, double salt, complex salt, and deliquescent salt.

1. Normal Salt

The salts formed by the loss of all possible protons of an acid (replaceable hydrogen atoms) are called normal salts. Such a salt does not contain a replaceable hydrogen atom, e.g.,\({\rm{NaCl,}}\,{\rm{NaN}}{{\rm{O}}_3},{{\rm{K}}_2}{\rm{S}}{{\rm{O}}_4},\) (one H-atom is not replaceable as \({{\rm{H}}_3}{\rm{P}}{{\rm{O}}_3}\) is a dibasic acid), \({\rm{Na}}{{\rm{H}}_2}{\rm{P}}{{\rm{O}}_2}\) (\({{\rm{H}}_3}{\rm{P}}{{\rm{O}}_2}\) is a monobasic acid), etc.

\({{\rm{H}}_2}{\rm{S}}{{\rm{O}}_4}\, + \,{\rm{NaOH}}\, \to {\rm{N}}{{\rm{a}}_2}{\rm{S}}{{\rm{O}}_4}\, + \,{{\rm{H}}_2}{\rm{O}}\)

2. Acidic Salt

Salts formed by incomplete neutralization of polybasic acids are called acid salts. Such salts still contain at least one or more replaceable hydrogen atoms. Examples:

\({\rm{NaHS}}{{\rm{O}}_4},\,{\rm{Na}}{{\rm{H}}_2}{\rm{P}}{{\rm{O}}_4},\) and \({\rm{N}}{{\rm{a}}_2}{\rm{HP}}{{\rm{O}}_4},\,\) etc. These salts, when neutralized by bases, form normal salts. This is because \({\rm{NaHC}}{{\rm{O}}_3}\) (an acid salt) \( + \,{\rm{NaOH}}\) (base) cannot exist together in a mixture.

\({{\rm{H}}_2}{\rm{S}}{{\rm{O}}_4}\, + \,{\rm{NaOH}}\, \to \,{\rm{NaHS}}{{\rm{O}}_4}\, + \,{{\rm{H}}_{\rm{2}}}{\rm{O}}\)
\({\rm{NaHS}}{{\rm{O}}_4}\, + \,{\rm{NaOH}}\, \to \,{\rm{N}}{{\rm{a}}_2}{\rm{S}}{{\rm{O}}_4}\, + \,{{\rm{H}}_{\rm{2}}}{\rm{O}}\)

Each acid salt has at least one replaceable hydrogen atom of the acid, which could not be replaced during neutralisation reaction is present in the acid salt thus formed.

3. Basic Salt

Salts formed by incomplete neutralisation of polyacidic bases are called basic salts. Such salts contain at least one or more hydroxyl groups. These salts, when neutralized by acids, form normal salts.

Examples: \({\rm{Zn(OH)Cl,}}\,{\rm{Mg(OH)Cl,}}\,{\rm{Fe(OH}}{{\rm{)}}_2}{\rm{Cl,}}\,\,{\rm{Fe(OH)C}}{{\rm{l}}_2},\,{\rm{Bi(OH}}{{\rm{)}}_2}{\rm{Cl,}}\) etc.

Example: \(1\) mole of \({\rm{Pb(OH}}{{\rm{)}}_2}\) requires \(2\) moles of \({\rm{HCl}}\) for complete neutralization. But when \(1\) mole of \({\rm{Pb(OH}}{{\rm{)}}_2}\) is made to react with \(2\) mole of \({\rm{HCl}}\) some \({\rm{Pb(OH}}{{\rm{)}}_2}\) is left unreacted. The salt produced is not \({\rm{PbC}}{{\rm{l}}_2}\), but \({\rm{Pb(OH)Cl}}\).

\({\rm{Pb}}{\left( {{\rm{OH}}} \right)_{\rm{2}}}{\rm{ + HCl}} \to \mathop {{\rm{Pb}}\left( {{\rm{OH}}} \right){\rm{Cl}}}\limits_{{\rm{lead}}\,{\rm{oxychloride}}} \,{\rm{ + }}\,{{\rm{H}}_{\rm{2}}}{\rm{O}}\)

Similarly, when one mole of \({\rm{Bi(OH}}{{\rm{)}}_3}\) is reacted with \(1\) mole of \({\rm{HN}}{{\rm{O}}_3}\) the salt \({\rm{Bi}}{({\rm{OH}})_2}{\rm{N}}{{\rm{O}}_3}\) is formed.
\({\rm{Bi}}{({\rm{OH}})_3}\, + \,{\rm{HN}}{{\rm{O}}_3}\, \to {\rm{Bi(OH}}{{\rm{)}}_2}{\rm{N}}{{\rm{O}}_3}\, + \,{{\rm{H}}_2}{\rm{O}}\)

Thus, a basic salt is formed when a polyacid base reacts with a lesser amount of acid than is necessary to form a normal salt.

4. Double Salt

The addition compounds formed by combining two simple salts in a stoichiometric ratio are called double salts. Such salt is stable in solid-state only and lose their identity in the solution state.

Some Example of Double Salts

5. Mixed Salt

A mixed salt contains more than one acid or basic ions other than hydrogen or hydroxyl ions.

Examples: sodium-potassium sulphate, disodium potassium phosphate.

6. Complex Salt

A complex salt is formed by the crystallisation from saturated salt solutions of two simple salts.

Examples: sodium argento cyanide, potassium mercuric iodide.

Deliquescent Salts

Some salts on exposure to the atmosphere absorb moisture from the atmosphere, dissolve in it and change into a liquid, such salts are called deliquescent salts.

Examples: Calcium chloride, magnesium chloride, zinc chloride, etc.

Properties of Salts

1. When dissolved in water, they furnish all the ions present in the simple salts from which it has been constituted.
2. When a double salt is dissolved in water, it dissociates into the constituent ions. For example, Mohr’s salt dissociates in solution as follows:

\({\rm{FeS}}{{\rm{O}}_4}{({\rm{N}}{{\rm{H}}_4})_2}{\rm{S}}{{\rm{O}}_4}.6{{\rm{H}}_2}{\rm{O}}{\mkern 1mu} {\rm{ + }}{\mkern 1mu} {\mkern 1mu} {\rm{water}}{\mkern 1mu} {\mkern 1mu}  \leftrightarrow {\mkern 1mu} {\rm{F}}{{\rm{e}}^{2 + }} + {\mkern 1mu} {\mkern 1mu} 2{\rm{NH}}_4^ +  + {\mkern 1mu} {\mkern 1mu} 2{\rm{SO}}_4^{2 – } + {\mkern 1mu} {\mkern 1mu} 6{{\rm{H}}_2}{\rm{O}}\)

Thus, an aqueous solution of Mohr’s salt gives the usual test of \({\rm{F}}{{\rm{e}}^{2 + }},{\mkern 1mu} {\rm{NH}}_4^ + ,\,{\mkern 1mu} {\rm{SO}}_4^{2 – }\) ions.

The solution of double salt, if present in the solution from which it has been constituted, shows all the properties of the simple salts. Double salts are obtained by mixing the saturated solutions of two simple salts followed by the crystallisation of their resultant saturated solution.

Preparation of Salts

1. By the reaction between acid and metal: \({\rm{HCl}}\) reacts with certain metals (such as zinc and magnesium) to produce salt and water.

\({\rm{Zn}}\,\,{\rm{ + }}\,\,{\rm{2HCl}}\,\, \to \,\,{\rm{ZnC}}{{\rm{l}}_2}\, + \,{{\rm{H}}_2} \uparrow \)

\({\rm{Zn}}\,\,{\rm{ + }}\,\,{{\rm{H}}_2}{\rm{S}}{{\rm{O}}_4}\,\, \to \,\,{\rm{ZnS}}{{\rm{O}}_4}\, + \,{{\rm{H}}_2} \uparrow \)

2. By the reaction between a base and acid: All acid-base reactions (neutralization reactions) produce salts.

\({\rm{NaOH}}\,\,{\rm{ + }}\,\,{\rm{HCl}}\,\, \to \,\,{\rm{NaCl}}\,\, + \,\,{{\rm{H}}_2}{\rm{O}}\)

\({\rm{CuO}}\,\,{\rm{ + }}\,\,2{\rm{HCl}}\,\, \to \,\,{\rm{CuC}}{{\rm{l}}_2}\,\, + \,\,{{\rm{H}}_2}{\rm{O}}\)

General Properties of Salts

1. Reaction with an acid: When a salt reacts with an acid, it produces another salt and acid. When sodium chloride is heated in the presence of sulphuric acid, sodium hydrogen sulphate (at low temperature) and sodium sulphate (at high temperature) are formed, and hydrogen chloride gas is evolved.

\({\rm{NaCl}}\,\,{\rm{ + }}\,\,{{\rm{H}}_2}{\rm{S}}{{\rm{O}}_4}\,\, \to \,\,{\rm{N}}{{\rm{a}}_2}{\rm{S}}{{\rm{O}}_4}\,\, + \,\,{\rm{HCl}}\,{\rm{(at }}\,{\rm{low }}\,{\rm{temperature)}}\)
\({\rm{2NaCl}}\,\,{\rm{ + }}\,\,{{\rm{H}}_2}{\rm{S}}{{\rm{O}}_4}\,\, \to \,\,{\rm{N}}{{\rm{a}}_2}{\rm{S}}{{\rm{O}}_4}\,\, + \,\,2{\rm{HCl}}\,{\rm{(at }}\,{\rm{high }}\,{\rm{temperature)}}\)

2. Reaction with a base: When salt reacts with a base, it produces a new salt and base.

\({({\rm{N}}{{\rm{H}}_4})_2}{\rm{S}}{{\rm{O}}_4}{\mkern 1mu} {\mkern 1mu}  + {\mkern 1mu} {\mkern 1mu} 2{\rm{NaOH}}{\mkern 1mu} {\mkern 1mu} \, \to {\mkern 1mu} \,{\mkern 1mu} {\rm{N}}{{\rm{a}}_2}{\rm{S}}{{\rm{O}}_4}{\mkern 1mu}  + {\mkern 1mu} {\mkern 1mu} 2{\rm{N}}{{\rm{H}}_4}{\rm{OH}}\)

3. Reaction with a metal: For example, when an iron nail is dipped into an aqueous solution of \({\rm{CuS}}{{\rm{O}}_4},\,{\rm{Cu}}\) gets deposited on the surface of the nail and the \({\rm{FeS}}{{\rm{O}}_4}\) formed remains in the solution.

\({\rm{CuS}}{{\rm{O}}_4}\, + \,\,{\rm{Fe}}\,\, \to \,{\rm{FeS}}{{\rm{O}}_4}\, + \,{\rm{Cu}}\, \downarrow \)

The fact that Fe is more reactive than Cu is demonstrated by this reaction.

4. The Behaviour of salts towards water: When a salt is dissolved in \({{\rm{H}}_2}{\rm{O}}\) the solution may be acidic or alkaline, neutral. It is dependent on the type of salt used.

(i) A neutral solution is produced by a normal salt formed from a strong base and a strong acid. For example, the aqueous solutions of sodium chloride and potassium sulphate are neutral.

(ii) A normal salt derived from a strong base and a weak acid gives an alkaline solution. For example, the aqueous solutions of sodium carbonate \(({\rm{N}}{{\rm{a}}_2}{\rm{C}}{{\rm{O}}_3})\) and sodium acetate \(({\rm{C}}{{\rm{H}}_3}{\rm{COONa}})\) are alkaline.

\({\rm{N}}{{\rm{a}}_2}{\rm{C}}{{\rm{O}}_3} + \,2{{\rm{H}}_2}{\rm{O}}\, \to \,{\rm{2NaOH}}\,{\rm{ + }}\,{{\rm{H}}_2}{\rm{C}}{{\rm{O}}_3}\)
\({\rm{C}}{{\rm{H}}_3}{\rm{COONa}}\,\, + \,{{\rm{H}}_2}{\rm{O}}\,\, \to \,\,{\rm{C}}{{\rm{H}}_3}{\rm{COOH}}\, + \,{\rm{NaOH}}\)

(iii) A salt derived from a weak base and a strong acid gives an acidic solution. For example, aluminium chloride \(({\rm{AlC}}{{\rm{l}}_3})\) and ammonium chloride \(({\rm{N}}{{\rm{H}}_4}{\rm{Cl}})\) make acidic aqueous solutions.

\({\rm{AlC}}{{\rm{l}}_3}\, + \,3{{\rm{H}}_2}{\rm{O}}\,\, \to \,{\rm{Al(OH}}{{\rm{)}}_3}\, + \,3\,{\rm{HCl}}\)
\({\rm{N}}{{\rm{H}}_4}{\rm{Cl}}\,{\rm{ + }}\,{{\rm{H}}_2}{\rm{O}}\,\,\, \to \,\,{\rm{N}}{{\rm{H}}_4}{\rm{OH}}\,\,{\rm{ + }}\,\,{\rm{HCl}}\)

Acidic salt solutions are acidic to litmus, causing the blue litmus paper to turn red. For example, a solution of \({\rm{NaHS}}{{\rm{O}}_4}\) turns blue litmus paper red. Sodium hydrogen carbonate \({\rm{(NaHC}}{{\rm{O}}_3}{\rm{)}}\) solution, however, is slightly alkaline.

\({\rm{pH}}\) of Salts

We know that an aqueous solution of sodium chloride is neutral; an aqueous solution of ammonium chloride \({\rm{N}}{{\rm{H}}_4}{\rm{Cl}}\) is acidic, whereas an aqueous solution of sodium carbonate \({\rm{N}}{{\rm{a}}_2}{\rm{C}}{{\rm{O}}_3}\) is basic or alkaline in nature. Though the aqueous solution of many salts is neutral, having a \({\rm{pH}}\) of \(7\) some salts produce acidic or basic solutions when dissolved in water. Based on the hydrolysis of salts, the acidic nature and basic nature of some salts are explained as follows:

(a) Salts of Strong Acid and Strong Base

Sodium chloride, potassium sulphate, sodium sulphate, sodium nitrate, etc., are the salts formed by strong acids and strong bases. The aqueous solutions of such types of salts are neutral, having a \({\rm{pH}}\) equal to \(7\). These do not undergo hydrolysis.
Example: Sodium chloride

\({\rm{NaOH  + }}\,{\rm{HCl }} \to \,{\rm{NaCl}}\,{\rm{ + }}\,{{\rm{H}}_2}{\rm{O}}\)

Since \({\rm{NaCl}}\) is formed from a strong \({\rm{HCl}}\) acid and a strong \({\rm{NaOH}}\) base, an aqueous solution of sodium chloride is neutral in nature.

(b) Salts of Strong Acid and Weak Bases

These salts, when dissolved in water, produces strong acid and weak bases. Thus, the aqueous solution of these salts is acidic in nature, having a \({\rm{pH}}\) of less than \(7\).

Example: Reaction of copper sulphate with water

\({\rm{CuS}}{{\rm{O}}_4}\,\, + \,\,{{\rm{H}}_2}{\rm{O}}\,\,\, \leftrightarrow \,\,{\rm{Cu}}\,{({\rm{OH}})_2}\, + \,{{\rm{H}}_2}{\rm{S}}{{\rm{O}}_4}\)

In this reaction, the copper sulphate is formed from a strong acid sulphuric acid and a weak base of copper hydroxide \({\rm{(Cu(OH}}{{\rm{)}}_2})\,\). An aqueous solution of copper sulphate is acidic in nature.

(c) Salts of Weak Acid and Strong Base

On dissolving in water, these salts produce a strong base and a weak acid having a pH of more than \(7\).
Example: Hydrolysis of sodium carbonate

\({\rm{N}}{{\rm{a}}_2}{\rm{C}}{{\rm{O}}_3}\, + \,2{{\rm{H}}_2}{\rm{O}}\,\, \leftrightarrow \,\,2\,{\rm{NaOH}}\,{\rm{ + }}\,{{\rm{H}}_2}{\rm{C}}{{\rm{O}}_3}\)

In this reaction, salt sodium carbonate is formed from a strong base sodium hydroxide and a weak acid, carbonic acid. An aqueous solution of sodium carbonate is basic in nature.

Sodium Chloride (Common Salt)

Chemically, the common salt is sodium chloride. It has the formula \({\rm{NaCl}}.\) It is a neutral salt. It is also called table salt. This is because it is used as an important food material. But actually, the table salt which we use is not pure sodium chloride; it also contains a small amount of potassium iodide. The table salt sold in the market contains iodine, and so it is labelled as iodized salt.

Occurrence

Common salt occurs naturally in seawater and as rock salt. Seawater contains several salts along with sodium chloride. Therefore, deposits of solid common salt are found in several parts of the world due to the solar evaporation of water.

Seawater

We know that seawater contains several salts dissolved in it. But how many of you know that most of the seawater is sodium chloride. To extract the salt from the seawater, it is trapped in the large shallow pools where the water is allowed to evaporate in the presence of sunlight and wind. The common salt is left behind. Since this salt obtained contains impurities of other salts like magnesium chloride and magnesium sulphate, the salt is therefore purified by removing these impurities by suitable methods. Thus, the common salt is obtained from seawater by the evaporation process.

Rock salt

Common salt is found in the form of solid deposits in Mandi of Himachal Pradesh in India and Khewra of Punjab in Pakistan. Beds of rock salts are formed due to the drying up of the sea of very olden times. Generally, the salt is dug out or pumped out by dissolving in water by sinking several concentric pipes into the salt bed. Due to the presence of impurities, it is often brown in colour and is called rock salt.

Properties of Common Salt

(i) It is a colourless crystalline substance.

(ii) Its melting point is \(801\,^\circ {\rm{C}}{\rm{.}}\)

(iii) Its solubility at room temperature is about \(35.8\,{\rm{g}}\) per \(100\,{\rm{g}}\) of water.

(iv) On heating, it produces a crackling sound.

(v) It is slightly hygroscopic in nature, i.e. it takes up moisture from the air and becomes wet due to the presence of magnesium chloride and calcium chloride.

Uses of Common Salt

Some of the important uses of common salt are as follows: It is used:

1. As an essential constituent of our diet.
2. As raw material for making many chemicals such as sodium hydroxide, sodium carbonate, hydrochloric acid, etc., in industries.
3. As a preservative for several food materials such as pickles, in curing meat and fish etc.
4. In the manufacture of soap.
5. In the preparation of pottery glaze.
6. To melt ice collected on the roads during winter in cold countries.
7. In cooking food, to improve the flavour of food.

Summary

Salts are ionic compounds consisting of two parts, namely, positively charged ions or cations, negatively charged ions or anions. In salts, the net charge of positive ions and the negative ions are equal, so salt is electrically neutral. The positive ion is usually a metal ion. In this article, we learned about types of salts, pH of salt solution, preparation, properties of salt, and uses of salts.

FAQs

We have provided some frequently asked questions about Salts here:

Q.1. How do you identify a salt?
Ans: A salt is defined as a compound that contains a cation and an anion. The simplest salts are compounds of one type of metal cation and one type of non-metal anion.
In chemistry, salt is a product of an acid-base reaction. Salt is made up of a positive ion from a base and a negative ion from an acid.

Q.2. Do salts conduct electricity?
Ans: Yes, salts conduct electricity in a molten state. Salts are mostly solids. They have a high melting point and boiling point. Salts are usually soluble in water. Just like acids and bases, solutions of salt in water conduct electricity. That is, salts are electrolytes. Salt solutions conduct electricity due to the presence of ions in them. Salts are ionic compounds. Every salt consists of a positively charged ion(cation) and a negatively charged ion (called anion). For example, sodium chloride salt consists of positively charged sodium ions and negatively charged chloride ions.

Q.3. What are the uses of salt?
Ans: Some of the important uses of common salt are as follows: It is used:
1. As an essential constituent of our diet.
2. As raw material for making many chemicals such as sodium hydroxide, sodium carbonate, hydrochloric acid etc., in industries.
3. As a preservative for many food materials such as pickles, curing meat and fish etc.
4. In the manufacture of soap.
5. In the preparation of pottery glaze.
6. To melt ice collected on the roads during winter in cold countries.
7. In cooking food, to improve the flavour of food.
8. It is used inzing mixture (i.e. \({\rm{NaCl}}\,{\rm{ + }}\) ice mixture) to attain less than \({0^ \circ }{\rm{C}}\) temperature.

Q.4. What are the types of salts?
Ans: A salt is a compound formed from an acid by the replacement of the hydrogen in the acid by a metal. A neutralisation reaction occurs when an acid and a base react. The term salt is also used to refer to common table salt, also known as sodium chloride.

Q.5. What are the types of salts?
Ans: The different types of salts are normal salt, acid salt, basic salt, mixed salt, complex salt and double salt.

Q.6. What is the formula of salt?
Ans: Sodium chloride, also known as salt, is a chemical compound with the formula \({\rm{NaCl}}\).

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