The chapter of electrochemistry is an interesting and scoring chapter of chemistry. It constitutes an important section for entrance examinations and ts prudent for the student not to neglect this. The concept of ionic equilibrium and chemical equilibrium forms the basis of learning the topic electrochemistry, which is an important topic from both JEE, and NEET point of view. The fundamental concepts of this topic can be built from NCERT class 11th and 12th book. For furthermore clarification or the concepts explained in even simpler language, students can refer to books of class 11th and 12th by the Maharashtra board.
What is ionic equilibrium?
Ionic equilibrium can be defined as equilibrium between the unionized molecules and the ions in the solutions of weak electrolyte.
Example: acetic acid breaking up into acetate ions and hydrogen ions:
CH3 COOH → CH3 COO– + H+
What are electrolytes?
These are the Chemical substances that can conduct electricity in their aqueous state or in molten state.
Types of electrolytes:
- Strong electrolytes: The electrolytes that are almost completely dissociated into ions in solution are called strong electrolytes. For example: KCl, HCl, NaOH, NH4NO3
- Weak electrolytes: These kind of electrolytes do not ionise completely in solution.it is called weak electrolytes.
Understanding the concept of ionic product:
In aqueous solution or in pure water, the product of concentrations of hydrogen and hydroxyl ions is a constant at a given temperature. This is called ionic product of water and is designated by Kw.
The idea of the ionic product of water can be understood by understanding the autoionization reaction of water that may be expressed as:
H2O+H2O=H3O+ +OH-H2O + H2O = H3O+ + OH–
Kw = CH3 O+ COH–
The value of Kw at 25°C is 1*10-14.
Subtopics that come under IONIC Equilibrium is:
- concepts of acids and bases and salts
- define conjugate acid-base pairs and identify them in an acid-base equilibrium
- derive the expressions for the ionization constants of weak acids and bases
- correlate the ionization constants and the strength of acids and bases
- explain self-ionization of water and derive an expression for its ionic product
- define pH and correlate it with the nature of aqueous solutions- neutral, acidic or basic
- define and explain common ion effect in ionization of weak acids and bases
- define buffer solutions
- Henderson equation to calculate the pH of acidic and basic buffers
- explain hydrolysis of salts with the help of chemical equations
- express solubility equilibrium with the help of an equation
- identifying relations between solubility and solubility product for salts of AB, AB2 A2B and A2B3 types
- understanding the concept of common ion effect on solubility equilibrium and Chemical Dynamics and recall some applications of common ion effect.
Summarizing few concepts:
1.IONIC equilibrium in short is the equilibria involving ionic species. The equilibria involved with acid and bases are used widely.
2.Buffer solutions resists a change in its pH on adding a small amount of an acid or a base. Using the buffer solutions for pH control is of great significance in living systems,agriculture and industrial processes. Likewise, the solubility equilibrium established in the solutions of sparingly soluble salts is also very important. Example our bones and teeth are mostly calcium phosphate, Ca3(PO4)2 is a slightly soluble salt.
3.SALTS: it is the product of reaction between acid and a base. Such reactions are called neutralization reaction.
(a) Normal salts The complete neutralization of normal salts between an acid with a base results in formation of normal salts, e.g., NaCI, K2SO4, etc.
(b) Acidic salts The incomplete neutralization of polybasic acids results in formation of acidic salts. e.g., NaHCO3, Na2SO4 etc.
(c) Basic salts The incomplete neutralization of polyacidic base results in the formation of basic salts, e.g., Mg(OH)Cl, Bi(OH)2Cl, etc.
(d) Double salts it is formed by the combination of two simple salts. This exist only in solid state, e.g., Mohr salt or ferrous ammonium sulphate (FeSO4.(NH4)2SO4.6H2O], alum, etc.
(e) Complex salts: it is formed by the combination of simple salts or molecular compounds. It is stable in solid state well as in solutions.
The properties of these solutions are different from the properties of substances from which they have been constituted.
(f) Mixed salts these are the ones of the salt that contains two salts in a fixed proportion. Common property of mixed salt shares either a common cation or common anion.
One cannot define acids and bases generally.Howeverthere are three different concepts of acids and bases proposed by Arrhenius, Brønsted and Lowry and Lewis respectivelywhich are well known.
It may not be the most important topic from both NEET and JEE point of view, but since it forms a basis for electrochemistry it should not be avoided in anyway. It is often observed that a question is asked in JEE MAINS and around 2-3 questions is asked in NEET EXAMS from time to time.
Can you answer the question: Which of thefollowing is a buffer solution?
- A) 500 mL of 0.1 N CH3COOH+500 mL of 0.1 N NaOH
- B) 500 mL of 0.1 N CH3COOH+500 mL of 0.1 N HCl
- C) 500 mL of 0.1 N CH3COOH+500 mL of 0.2 N NaOH
- D) 500mLof0.1NCH_(3)COOH+500mLof0.1NNaOH