Course Content
Section Name Topic Name 3 Classification of Elements and Periodicity in Properties 3.1 Why do we Need to Classify Elements ? 3.2 Genesis of Periodic Classification 3.3 Modern Periodic Law and the present form of the Periodic Table 3.4 Nomenclature of Elements with Atomic Numbers > 100 3.5 Electronic Configurations of Elements and the Periodic Table 3.6 Electronic Configurations and Types of Elements: s-, p-, d-, f – Blocks 3.7 Periodic Trends in Properties of Elements
Section Name Topic Name 7 Equilibrium 7.1 Equilibrium in Physical Processes 7.2 Equilibrium in Chemical Processes – Dynamic Equilibrium 7.3 Law of Chemical Equilibrium and Equilibrium Constant 7.4 Homogeneous Equilibria 7.5 Heterogeneous Equilibria 7.6 Applications of Equilibrium Constants 7.7 Relationship between Equilibrium Constant K, Reaction Quotient Q and Gibbs Energy G 7.8 Factors Affecting Equilibria 7.9 Ionic Equilibrium in Solution 7.10 Acids, Bases and Salts 7.11 Ionization of Acids and Bases 7.12 Buffer Solutions 7.13 Solubility Equilibria of Sparingly Soluble Salts
Section Name Topic Name 10 The s-Block Elements 10.1 Group 1 Elements: Alkali Metals 10.2 General Characteristics of the Compounds of the Alkali Metals 10.3 Anomalous Properties of Lithium 10.4 Some Important Compounds of Sodium 10.5 Biological Importance of Sodium and Potassium 10.6 Group 2 Elements : Alkaline Earth Metals 10.7 General Characteristics of Compounds of the Alkaline Earth Metals 10.8 Anomalous Behaviour of Beryllium 10.9 Some Important Compounds of Calcium 10.10 Biological Importance of Magnesium and Calcium
Section Name Topic Name 12 Organic Chemistry – Some Basic Principles and Techniques 12.1 General Introduction 12.2 Tetravalence of Carbon: Shapes of Organic Compounds 12.3 Structural Representations of Organic Compounds 12.4 Classification of Organic Compounds 12.5 Nomenclature of Organic Compounds 12.6 Isomerism 12.7 Fundamental Concepts in Organic Reaction Mechanism 12.8 Methods of Purification of Organic Compounds 12.9 Qualitative Analysis of Organic Compounds 12.10 Quantitative Analysis
Class 11th Chemistry Online Class: Elevate Your CBSE Board Success
About Lesson

Acids, bases and salts

The Substances that get dissociated are broadly classified into three types:

  • Acids
  • Bases
  • Salts

Acids: Are those that are sour and turn blue litmus red.

Bases: Are those that are soapy in touch and turn red litmus blue.

Salts: Are those that are formed when acid and base react.

But this information is not relevant or sufficient to classify substances. So, we have different concepts and attempts in order to classify the substances.

1st concept: Arrhenius concept of acids –bases

According to Arrhenius:

Acids are those substances which when dissolved in water produce hydrogen ions.

Example: HCl àH+ + Cl

Later on, it was said that this hydrogen ions combines with water to form hydronium ion i.e. H3o+

Bases: Are those which when dissolved in water, release hydroxide ions.

Example: NaOHàNa+ + OH

Later on, it was seen that there are few substances that do not release hydrogen or hydroxide ion. But, still they behave as acids or bases .So, another concepts were introduced.

2nd Concept: Bronsted Lowry concept

According to it:

Acids:  Which give hydrogen ion in solution (as they are proton donors).

Example: HClàH+ + Cl

Bases: Are those which are proton acceptors.

Example: NH3 + H+ àNH4+

Conjugate acid –base concept: If any strong acid dissociates, it will produce weak conjugate base that is:

HClàH+ + Cl

(HCl is strong acid)(Cl is conjugate base)

Or we can say :

Acid – H+ àconjugate base

Base + H+à conjugate acid 

There are certain substances that behave as acids as well as bases, they are called Amphoteric substances.

Example: H2O + H+àH3O+

                 (Base)           (Conjugate acid)

                H2OàH+ + OH

               (Acid)          (Conjugate base)

3rd concept: Lewis concept

According to him:

Acids: They are those which accept a pair of electron.

For example: substances that falls in this category:

  • Cations like ammonium ion etc
  • All neutral electron deficient compounds like BF3, AlCl3 etc
  • All those which have empty d orbital like SF4 etc
  • All those different elements with different electro-negativities but bonded with multiple bonds like carbon dioxide etc.

Bases: Are those that are electron donors. They are of two types:

  • Anions like chloride ions etc
  • All neutral species having lone pair of electrons like water etc

Limitation of this concept: There are many substances which are Lewis bases and acids, but they may not be Arrhenius acid or base or Lowry acid or base.

Equilibrium notes class 11 and ncert solution for excel in the exam
equilibrium notes class 11

Please note:

  • Acid + water à concentration of hydronium ion is more than hydroxide ion.
  • Base + water à concentration of hydronium ion is less than hydroxide ion.
  • Pure water à concentration of hydronium ion and hydroxide ion is same.

Expressing Hydrogen ion concentration: pH scale

To know nature of any substances, we use pH scale.

pH of solution: It is defined as negative of logarithm of hydrogen ion concentration.

 Mathematically:- pH = – log[H3O]+

pH is a measure of acidic or basic strength of any solution.

pH scale is given below:

Scale is just like a number line on which there is a reading ranging from 0 to 14.

  • Up to 7: acidic
  • At 7: neutral
  • Above 7 : basic
  • All solutions having pH 4 to 7 : weak acid
  • pH 2 to 4 : moderately acidic
  • pH 7: neutral
  • pH less than 2: strong acid
  • pH =14: strong base
  • pH 7 to 9: weak base

         Calculation of pH:

pH = – log[H3O]+

equilibrium notes class 11
equilibrium notes class 11
equilibrium notes class 11
Wisdom TechSavvy Academy