Learn about the basics of acids, bases, and salts in a simple and easy-to-understand way. Discover their properties and how they interact to form various chemical reactions. Get a solid foundation in chemistry with our user-friendly guide.
Acid-Base and Salt
Acid: The word acid is derived from the Latin word acids which means sour. Those substances that give Hydrogen ions (H+ )in an aqueous solution are called acids.
Base: Those substances that give hydroxyl ions (OH¯) in an aqueous solution are called a base.
Salt: The chemical compound that is formed due to the neutralization reaction of acid and base is called salt. A salt consists of positive ions from the base and negative ions from an acid, both positive and negative ions combine and form is salt.
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Properties of Acid
The following are some important properties of acid.
(i) Acids have a sour taste.
(ii) It turns blue litmus paper into the red.
(iii) It changes the color of acid-base indicators.
(iv) Aqueous solution of acid conducts electric current.
(v) Strong acids are corrosive and have a skin-burning effect.
(vi) They have a pH value of less than 7.0.
(vii) They react with metals from salt and hydrogen gas.
Properties of Bases
The following are some important properties of bases.
(i) Bases are bitter in taste.
(ii) They have a soapy or slippery feel.
(iii) It turns red litmus paper into the blue.
(iv) It changes the color of acid-base indicators.
(v) Aqueous solution of bases conducts electric current.
(vi) Strong bases are very corrosive.
(vii) They have a pH value greater than 7.0.
Alkalis: A water-soluble base is called alkalis, all alkalis are bases but all bases are not alkalis.
Various concepts about Acid and Bases
Arrhenius's concept of acid and bases
Arrhenius's concept of acids:- according to this concept those substances that ionize in an aqueous solution and produce (H+) ions are called acids. Example:- HCl, HNO3, H2SO4, HCN, CH3COOH, etc.
Arrhenius's concept of bases: Those substances that are ionized in an aqueous solution and produce hydroxyl ions (OH¯) are called acids. Example:- KOH, NaOH, NH4OH, Ca(OH)2, etc.
Limitation of Arrhenius's concept
The following are the limitations of the Arrhenius concept.
(i) This concept is only limited to aqueous solutions.
(ii) It does not explain the acidity and basicity of the non-aqueous solution.
(iii) It can not explain the acidic character of AlCl3, CO2, SO2, etc., and the basic nature of MgO, NH3, etc.
Bronsted and Lowery concept of Acid and Bases
Acid:- Those substances that donate or tend to donate proton [H+] ions are called Bronsted and Lowery acids.
Bases:- Those substances that accept or tend to accept proton [H+] ions are called Bronsted and Lowery bases.
Example:- Considered the reaction between hydrochloric acid (HCl) and ammonia in the aqueous medium. HCl + NH3 ⟶ NH4 + Cl .
In this reaction, HCl donates the proton (H+) ion and acts as an acid while NH3 accepts the proton (H+) ion to form an ammonia ion (NH4) and act as a base.
Limitation of Bronsted and Lowery concept
The following are the limitations of Bronsted and Lowery's concept of acids and bases.
(i) This concept can not explain the reactions that occur in a non-photonic solvent such as SO2, CCl4, or C6H6. etc.
(ii) It can not explain the behavior of acidic oxides such as CO2, SO3, NO2, etc., and oxides such as MgO, BaO, etc.
Lewis's Concept of Acid and Bases
Acid: According to Lewis's concept. Those species (molecules or ions) that can accept a pair of electrons are called acids.
Bases: Those species (molecules or ions) that can donate a pair of electrons are called bases.
Explanation of Lewis's Concept
An acid-base reaction involves the donation of electrons pair from a base to an acid-forming coordinate covalent bond, the coordinate covalent bond is always formed between electron donor and electron acceptor species. So the compound that is electron deficient behaves as Lewis acid while the compounds that have a lone pair of electrons or negatively charged ions behave as Lewis base.
Example of Lewis acid and bases: Considered the reaction between BF3 and NH3
In this reaction, BF3 accepts a pair of electrons to act as a Lewis acid while in NH3 nitrogen donates a pair of electrons forming a coordinate covalent bond and acting as a Lewis base.
Types of Acids
The following are the types of acids.
(i) Monoprotic Acid:- The acids that donate only one proton per molecule is called monoprotic acid.
Example:- HCL ⟶ H+ + Cl¯
HNO3 ⟶ H+ + NO3¯
(ii) Polyprotic acids:- Those acids that donate more than one proton per molecule are called polyprotic acids. It may be divided into diprotic acid and triprotic acids.
Diprotic Acids:- Those acids that donate two protons per molecule are called diprotic acids.
Example: H2SO4 ⟶ 2H+ + SO4¯²
Triprotic Acids:- Those acids that donate three protons per molecule are called triprotic acids.
Example: H3PO4 ⟶ 3H+ + PO4￣3^
Type of Bases
The following are the types of bases. (i) Monoacidic bases (ii) Poly-acidic bases
(i) Monoacidic bases:- Those base that produces one hydroxyl ion per molecule is called monoacidic bases.
Example:- NaOH ⟶ Na+ + OH¯
(ii) Poly-acidic bases:- Those bases that produce more than one hydroxyl ion per molecule are called poly-acidic bases. It may be divided into di-acidic bases and tri-acidic bases.
Example of di-acidic. Mg(OH)2 ⟶ Mg+ + + 2OH¯
Example of Tri-acidic. Al(OH)3 ⟶ Al+++ + 3OH¯
Conjugate of Acid and Base
Conjugate Acids:- A species formed from an acid by the loss of a proton is called the conjugate base of that acid.
Explanation:- When an acid donates a proton it forms a negative charge species which can accept the proton and act as a base called the conjugate base of the corresponding acid.
Exam. CH3COOH + H2O ⟶ CH3COO¯ + H3O+
Conjugate Bases:- A species formed from a base by gaining a proton is called the conjugate acid of that base.
Explanation:- When a base accepts a proton then it forms positive charge species which can donate a proton and act as acids called conjugate acid of the corresponding base.
Exam. NH3 + H2O ⟶ NH4 ๋ + OH¯
Strength of acid and base
Strong acid:- Those acids that completely dissociate or ionize completely in an aqueous solution and produce a higher concentration of (H+) ions are called strong acids. Hydrochloric acid, Sulphuric acid, Nitric acid. etc.
Weak Acid:- Those acids that partially dissociate or ionize in an aqueous solution and produce a low concentration of (H+) ions are called weak acids. Acetic acid, Carbonic acid, Propanoic acid. etc.
Strong Bases:- Those bases that completely dissociate or ionize in an aqueous solution and produce higher concentrations of hydroxyl ions (OH¯) are called strong bases. Sodium hydroxide, Potassium hydroxide, Lithium hydroxide. etc.
Weak bases:- Those bases that partially dissociate or ionize in an aqueous solution and produce a low concentration of hydroxyl ions (OH¯) are called a weak base. Ammonium hydroxide, Calcium hydroxide, Aluminum hydroxide, etc.
Preparation of Salt
There are two types of salt preparation. (i) Soluble salt and (ii) Insoluble salt.
(i) Preparation of soluble salt:-
Soluble salt can be prepared by the following four methods
(a) By the action of an acid and a metal:- In this method, highly reactive metals such as Mg, Ca, Zn, etc. replaced hydrogen ions of acid and produced salts and hydrogen gas.
Exam. 2HCl + Mg ⟶ MgCl + H2↑
(b) By the reaction of acid and bases:- In this method, acid reacts with base and neutralizes the effect of each other and produces salt and water.
Exam. HCl + NaOH ⟶ NaCl + H2O
(c) By the reaction of an acid and metallic oxide:- The metallic oxides such as (CuO, CaO, and MgO) react with dilute acid to form salt and water.
Example: H2SO4 + 2CaO ⟶ CaSO4 + H2O
(d) By the reaction of an acid and carbonate:- Dilute acid reacts with carbonates such as sodium carbonate or sodium hydrogen carbonate to produce salt water and carbon dioxide.
Example: 2HCl + Na2CO3 ⟶ 2NaCl + H2O + CO2
(ii) Preparation of Insoluble Salts
Insoluble salt is usually obtained during the chemical reaction by mixing two soluble salts, during this reaction exchange of ions takes place and two new salts are produced one is soluble and the other is insoluble the insoluble salt precipitate at the bottom, of the solution.
Example: AgNO3 + NaCl ⟶ AgCl(3) + NaNO3
Different types of salt
There are three main types of salts. (i) Neutral salts (ii) Acidic salts (iii) Basic salts.
(i) Neutral Salts
The type of salts that are formed when the hydrogen ions of acid are completely replaced by metal ions or a group of atoms that behave like metal ions is called neutral salts.
Explanation of natural salts:- Neutral salts are formed when a strong acid and a strong base is neutralized in the reaction for example sodium chloride is formed by the neutralized reaction of hydrochloric acid and sodium hydroxide.
HCl + NaOH ⟶ NaCl + H2O
The following are examples of neutral salts. Potassium sulfate, Sodium Sulphate, Sodium carbonate, etc.
(ii) Acidic Salts
The type of salts that are formed when the hydrogen ions of acid are partially replaced by metal ions or a group of atoms that behave like metal ions are called acidic salts, acidic salts are formed by polybasic acid only. These salts further react with bases and form neutral salts.
H2SO4 + KOH ⟶ KHSO4 + H2O
(iii) Basic Salts
This type of salt which is formed when partially neutralized of a strong base by a weak acid is called basic salt. These salts contain ionized H+ ions along with another cation. Mostly the ionized H+ comes under the part of an anion. A few acid salts can be used in baking. For example, KH2PO4, NaHSO4, etc.
H2SO4 + NaOH → NaHSO4 + H2O