Sunday, December 29, 2019

JEE Main - Core Points for Revision - Ch. 8. Equilibrium II – Ionic Equilibrium in Solutions


Importance of  Core Revision Points: Core Revision Points are important because if you remember them strongly, many more points related to them will come out of your memory and help you to answer question and problems. Read them many times and make sure you remember them very strongly.


8.1 Acid-base Concepts

Acids and bases definitions (Arrhenius, Bronsted and Lewis)

Arrhenius defined acid as a hydrogen compound which in water solution give hydrogen ions.
He defined base as a hydroxide compound which in water solution gives hydroxide ions.


Lowry and Bronsted
An acid is defined as a substance having a tendency of lose or to donate one or more protons.
A base is defined as a substance having a tendency to accept or add a proton


Lewis Theory of Acids and Bases

Acid: An acid is any substance (molecule, ion or atom) that can accept a lone pair of electrons to form a coordinate bond (*Remember coordinate bond and lone pair topics in chapter on Bonding)

Base: Base is any species (molecule, ion or atom) that can donate a lone pair of electrons to form a co-ordinate bond.

8.2 Acid- base Equilibria and Ionization of Acids and Bases


8.3 Ionization of Water – Ionic Product of Water


Ionic Product of Water

The Ionic Product of Water, Kw, is the equilibrium constant for the reaction in which water undergoes an acid-base reaction with itself. That is, water is behaving simultaneously as both an acid and a base.

H2O(l) + H2O(l) = H3O+(aq) + OH-(aq)

Kw = [H3O+(aq)][OH-(aq)]

At 298 K, the value of Kw is 1 x 10-14 mol^2 dm^-6. This makes the concentration of H+ ions equal to 1 x 10-7 mol dm^-3, and therefore the pH is 7. This is defined as 'neutral'.

From the above equilibrium expression, taking -log10 throughout

pKw = pH + pOH = 14

Ionic Product does not apply only to water. It applies, for example, to the equilibrium in liquid ammonia:

NH3 + NH3 = NH2- + NH4+

8.4 Expressing Hydrogen Ion Concentration – pH Scale


pH

pH is related to hydrogen ion concentration. Since the H+ ion concentration in solution is often small, the concentration is generally expressed as the logarithm of its reciprocal, which is called a pH value. Therefore, pH is defined as

pH = -log[H+]

For a ten times increase in H+ ion concentration there is a decrease in the pH value of one unit.

Given the pH of a solution, its H+ concentration can be found:

[H+(aq)] = antilog -pH


or

[H+(aq)] = 10^-pH



8.5 Polyprotic Acids and Bases

8.6 Hydrolysis of Salts
Hydrolysis is the name for a substance chemically reacting with water.

Hydrolysis should be distinguished from solvation, which is the process of water molecules associating themselves with individual solute molecules or ions.

When a chemical reaction comes to equilibrium, there is a mixture of all involved substances in the reaction vessel. This mixture is characterized by a constant composition. (constant composition DOES NOT imply equal composition.)

The key point that makes a reaction come to equilibrium is that it is reversible. This means that both the forward reaction and the reverse reaction can happen,
The reaction comes to equilibrium when the rates of the two reactions (forward and reverse) become equal.
More details  https://iit-jee-chemistry.blogspot.com/2008/02/jee-revision-hydrolysis-of-salts.html

8.7 Acid base Titrations and Indicators

8.8 Solubility Product


Solubility product of a salt at a given temperature is equal to the product of the concentrations of its ions in the saturated solution, with each concentration term raised to the power equal to the number of moles of ions produced on dissociation of one mole of the substance.

More details https://iit-jee-chemistry.blogspot.com/2008/02/solubility-product.html

8.9 Buffer Solution






Sections in the Chapter

8.1 Acid-base Concepts
8.2 Acid- base Equilibria and Ionization of Acids and Bases
8.3 Ionization of Water – Ionic Product of Water
8.4 Expressing Hydrogen Ion Concentration – pH Scale
8.5 Polyprotic Acids and Bases
8.6 Hydrolysis of Salts
8.7 Acid base Titrations and Indicators
8.8 Solubility Product
8.9 Buffer Solution


Updated on 2 January 2020
21 May 2015

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