Ionic-Equilibria-Class-12th-Chemistry-Notes.pdf - PAWAN ...

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Ionic equilibria:-

The equilibrium between ions and unionized molecules in

the solutions is called as ionic Equilibria.

Unionized Ions

molecule

Ionic equilibria

Substance/Electrolyte

PAWAN WAGH ACADEMY Notes

Topic – IONIC EQUILIBRIA

Strong Electrolyte

The electrolytes which

ionizes completely in

aqueous solution are

called as strong

electrolytes.

Ex: - Strong Acid, Strong

Base

Weak Electrolyte

The electrolytes which do

not ionizes or dissociates

completely in aqueous

solution are called as weak

electrolytes.

Ex: - Weak Acid, weak

Base


Degree of dissociation (α):-

The ratio of number of moles dissociated to the total

number of moles is called as degree of dissociation (α).

α = 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑚𝑜𝑙𝑒𝑠 𝑑𝑖𝑠𝑠𝑜𝑐𝑖𝑎𝑡𝑒𝑑

𝑇𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑙𝑦𝑡𝑒

Percentage Dissociation (% α)

For solving, numerical, generally we use ‘α’ for calculations,

and not % α

Various theory for Acids and Bases

Arrhenius Bronsted Lewis theory

Theory Lowry

Theory

Arrhenius theory :-

Acid- Substance which gives H+

ions in aqueous solution.

Ex:- HCL Water H+

+ Cl-

Base- Substance which gives OH-

ions in aqueous solution.

Ex:-NaOH water Na+

+ OH-

α% = αx100


Bronsted- Lowry theory:-

Acid- Substance which donate H+

ion to other substance.

Base – Substance which accept H+

ion from other

substance.

Ex- HCl + NH3 Cl-

+ NH4

(+)

Acid Base

donates accepts

H+

Ion H+

ion conjugate conjugate

Base Acid

Conjugate Base :- The base which is produced, when acid

donates H+

ion is called as Conjugated base.

Conjugate Acid

The acid which is produced, when base accept H+

ion is called

as Conjugated Acid.

-H+

+ H +

Lewis theory

Acid: - The species which accept shared electron pair.

Base: - The species which donate shared electron pair.

ex:

Acid

Conjugated Acid

Conjugated Base

Base


Amphoteric Nature

The nature in which, the substance shows both acidic as

well as basic behavior is called as amphoteric nature.

Dissociation of strong acid and strong base and

weak acid and base weak Base

Strong Acid or Strong Base

(Represented By single Arrow)

Weak Acid or Weak Base

(Represented By double Arrow)

Examples

Constant =

[Product ]

[Reactant]

A + B C + D Normal Reactions

A + B C + D Dissociation Reactions

Reactants Products

Strong Acid

HCl,HNO3,

H2SO4,HBr,HI

Weak Acid

HF,HCOOH,

CH3COOH,H2S

Strong Base

NaOH,KOH

Weak Base

Fe(OH)3,

Cu(OH)2


Dissociation of

Weak Acid Weak Base

HA H+

+ A-

BOH B+

+ OH-

Ka=(H+) (A−)

(𝐻𝐴) Kb =

(𝐵+)(𝑂𝐻−)

(𝐵𝑂𝐻)

Ka = Dissociation constant Kb = Dissociation Constant

of acid of Base

Ostwald’s dilution Law

For weak Acid

HA H+

+ A-

Initial amount 1 0 0

Amount of equilibm

1-α α α

Conc 1−𝛼

𝑣 𝛼

𝑣 𝛼

𝑣

Ka = [𝐻+][𝐴−]

[𝐻𝐴]

= (𝛼

𝑉)(

𝛼

𝑉)

= (1−𝛼

𝑉)

= 𝛼2

(1−𝛼)𝑣for dilute solution

= 𝛼

𝑣(1) [1-α≅] and also

Ka = α2

c 1

𝑣 = c

or

For weak Base

BOH B+ OH-

Initial amount 1 0 0

Amount at equilibm 1-α α α

Concentration 1−𝛼

𝑣

𝛼

𝑣

𝛼

𝑣

Ka = [𝑂𝐻−][𝐵+]

[𝐵𝑂𝐻]

=(∝

𝑉)(

∝

𝑉)/

1−∝

𝑉

= ∝2

(1−∝)𝑉

= ∝2

1𝑥𝑣 for dilute soln (1-∝≅ 1)

Kb = ∝2C 1

𝑉= 𝑐

or


Autoionization of water

H2O + H2O ⇌ H3O+

+ OH-

Equilibrium constant = Keq = [𝑃𝑟𝑜𝑑𝑢𝑐𝑡]

[𝑅𝑒𝑎𝑐𝑡𝑎𝑛𝑡] = [H3O

+

][OH-

] /[H2O]2

So [H3O+

] [OH-

] = keq x [H2O]2

………….. [H2O]2

= K’’=constant

[H3O+

] [OH+

] = Keq x K’’

Or

Ionic product of water = Kw = [H+

] [OH-

] = 1x10-14

Some important Formula

1. PH

= -log10 [H+

]

2. POH

= -log10 [OH-

]

3. Kw = [H+

] [OH-

]= [H3O+

] [OH] = 1x10-14

4. PH

+ POH

= 14 (PH

scale)

α= √𝑘𝑎

𝑐 α = √𝑘𝑎𝑋𝑉

∝= √𝐾𝑏

𝐶

∝= √𝐾𝑏𝑥𝑣

[H3O+

] [OH-

] = Kw

Kw = [H+

] [OH-

]


Types of solution

Acidic Neutral or Basic

Solution alkaline solution

solution

PH

<7 PH

=7 PH

>7

[H+

]>10-10

[H+

]=[OH-

]=10-7

[H+

]<10-7

Types of salt

SA= strong acid

SB= Strong base

WA= Weak acid

WB= weak base

SA+SB salt + H2O

HCl+NaOH NaCl +H2O

H2SO4+2NaOH Na2SO4+H2O

HNO3+NaOH NaNO3+H2O

HCl + KOH KCl + H2O

HNO3 + KOH KNO3 + H2O

WA+SB salt + H2O

CH3COOH+NaOH CH3COONa+H2O

HCN + KOH KCN+H2O

H2CO3+NaOH Na2CO3+H2O


SA+WB Salt + H2O

HCL+NH4OH NH4Cl+ H2O

H2SO4+Cu(OH)2 CuSO4+ H2O

HNO3 + NH4OH NH4NO3+ H2O

2HCl + Cu(OH)2 CuCl2 + H2O

WA+WB Salt + H2O

CH3COOH+NH4OH CH3COOH+H2O

HCN + NH4OH NH4CN + H2O


Hydrolysis Concept

Hydrolysis of salt

The reactions in which or anions or both ion of salt react

with ions of water is called as Hydrolysis of salt.

Hydrolysis of salt of

Weak acid and weak

Base

Ka>Kb Ka<Kb Ka=Kb

HF+NH4OH NH4F+H2O HCN+NH4OH CH3COOH+NH4OH

NH4CN+H2O CH3COONH4

Strong acid and

strong base

HCl+NaOH NaCl+H2O

Strong Acid And

Weak Base

H2SO4+Cu(OH)2 CuSO4+H2O

Weak acid and

strong Base

CH3COOH+NaOH

CH3COONa+H2O


Steps involved while doing hydrolysis of any salt

Acid + Base Salt + H2O

Salt Cation + Anion

(C+

) Cation + H2O C(OH) + H+

or H3O+

H+ OH- Base

A-

(Anion) + H2O AH + OH-

H+

OH- Acid


I) Hydrolysis of salt of strong acid and strong base

HCl + NaOH NaCl + H2O

SA SB Salt

NaCl Na+

+ Cl-

Here cation and anion formed are from strong acid

and strong base, so they do not undergoes hydrolysis

so [H3O+

]=[OH-

]

and nature of solution is neutral.

II) Hydrolysis of salt of strong acid and weak base

H2SO4 + Cu(OH)2 Cu(SO4)2 + H2O

SA WB salt

Cu(SO4)2 Cu+2

+ 2 SO4

2-

Cu+2

(cation) is from Cu(OH)2

Cu(OH)2 is a weak base, so Cu+2

undergoes

hydrolysis

Cu+2

+ H2O Cu(OH)2 + H3O+

or H+

As the acid is strong, so nature of solution is

acidic

So [H3O+

]>[OH-

]


III) Hydrolysis of salt of weak acid and strong base

CH3COOH + NaOH CH3COONa + H2O

Weak acid Strong Salt Water

Base

CH3COONa CH3COO(-)

+ Na(+)

Anion cation

As CH3COO(-)

anion comes from acid (CH3COOH)

As CH3COOH is a weak acid, so CH3COO-

ion

undergoes hydrolysis

CH3COO-

+ H2O CH3COOH + OH-

In the solution base is strong, so the nature of solution

is basic

IV) Hydrolysis of salt of weak acid and weak base

In case of weak acid and weak base, the cation and

anion both undergoes hydrolysis as both acid and

bases are weak

Ka>Kb Kb>Ka Ka=Kb

Ka= dissociation = constant for acid

Kb = Dissociation = constant for base

3 cases


Hydrolysis of weak acid and weak base

Ka>K

b

HF + NH4OH → NH

4F + H

2O

Acid Base salt

NH4F ⇌ NH

4

+ + F

-

cation anion

NH4

++ H

2O ⇌ NH

4OH + H

3O

+

F- + H

2O ⇌ HF + OH

-

NH4

+

hydrolysis F

-

higher than , So more H3

O

+

is formed , So solution

is acidic in nature , So Ka

>Kb

Kb> K

a

HCN + NH4OH → NH

4CN + H2O

Acid Base Salt

NH4CN ⇌ NH

4

+ + CN

-

Cation anion

NH4

+ + H2O ⇌ NH

4OH + H

3O

+

CN- + H

2O ⇌ HCN + OH

-

CN- hydrolysis to higher extent than NH

4

+, So more OH

- is formed , So solution is basic in

nature, So Kb>K

a

Kb= K

a

CH

3COOH + NH

4OH → CH

3COONH

4 + H

2O

Acid Base Salt

CH3COONH

4 ⇌ CH

3COO

- + NH

4

+

Anion Cation

CH3COO

- + H

2O ⇌ CH

3COOH + OH

-

NH4

+ + H

2O ⇌ NH

4OH + H

3O

+

CH3COO

- and NH

4

+ ion hydrolysis to same extent, So H

3O

+ and OH

- are equally formed , So

solution is neutral and so Kb

= Ka


Buffer

The solution which do not change its PH

, when small

amount of strong acid or strong base is added to it,

is called as buffer solution.

Types of Buffer solution

Acidic buffer solution Basic buffer solution

A solution which A solution which contains

contains

is called as acidic buffer solution is called as basic buffer solution

Properties of Buffer

pH do not change

Weak acid + salt of weak

acid and strong base

Weak base + salt of weak

base and strong acid

pH=pKa + log10[𝑠𝑎𝑙𝑡]

[𝑎𝑐𝑖𝑑] pOH= pKb + log10

[𝑠𝑎𝑙𝑡]

[𝐵𝑎𝑠𝑒]

pKa = -log10Ka pKb

= -log10Kb

By addition of

strong acid or

strong base

By addition of

H2O(dilution)

By keeping it

for long time


Application of buffer

Solubility equlibria:-

The equilibria that exist between the undissolved solid and

dissolved ions in solution is called as solubility equilibria.

Sparingly soluble compounds

The compound that dissolve slightly in water, is called as

sparingly soluble compound

Solubility product

The product of concentration of ions in a saturated

solution is called as solubility product (Ksp).

Ksp for AgCl = [Ag+

][Cl-

]

AxBy xAy+

+ YBx-

Ex: BaSO4 1Ba+2

+ 1SO4

2-

…….Ksp= [Ba+2

][SO4

2-

]

Ex: CaF2 1Ca+2

+ 2F1-

…… Ksp= [Ca+2

][F1-

]2

Ex: Bi2S3 2Bi+3

+ 3S2-

……….Ksp= [Bi+3

]2

[S2-

]3

In

biochemical

system

Agriculture Industry Medicine

Analytical

chemistry

Undissolved solid ⇌dissolved ions


Solubility:-

The ratio of amount of solute in grams per unit volume of

solution is called as solubility.

Unit of solubility = 𝑔𝑟𝑎𝑚

𝑙𝑖𝑡𝑟𝑒

Molar solubility:-

The ratio of solubility in g/L per unit molar mass is

called as molar solubility

Unit of molar solubility is 𝑚𝑜𝑙

𝑙𝑖𝑡𝑟𝑒

Imp Relation

/ (molecular mass)

Solubility molar solubility

(𝑔

𝑙) (

𝑚𝑜𝑙

𝑙)

X (molecular mass)

Ksp=Xx

.Yy

.Sx+y

In case of Bx Ay X B+y

+ Y Ax-

So

Where S= Solubility

Ksp=[B+y

]x

[Ax-

]y .

Sx+y


For example

1. For AgBr

Ag1Br1 1Ag1+

+ 1Br1-

So Ksp = (1)1

(1)1

S1+1

= S2

= Ksp

2. For Pb I2

Pb I2 1Pb+2

+ 2I1-

So ksp = (1)1

(2)2

S1+2

= 4S3

=Ksp

3. For Al(OH)3

Al(OH)3 1Al+3

+ 3(OH1-

)

So Ksp = (1)1

(3)3

. S1+3

= 27 S4

= Ksp

Condition of precipitation

IP=ksp

Solution is

saturated

Equilibrium

exist

IP>Ksp

Solution is

supersaturated

Precipitation

occurs

IP<Ksp

Solution is

unsaturated

Precipitation do

not occurs


Common ion effect:-

Let CH3COOH be the weak acid.

CH3COOH be the salt of weak acid and strong base.

CH3COOH dissociates very less, as it is weak acid

CH3COONa dissociates completely, as it is stronger

salt

As below:-

CH3COOH CHCOO(-)

+ H(+)

less CH3COO(-)

ions

are formed

CH3COONa CH3COO(-)

+ Na(+)

more CH3COO(-)

ions

are formed

So in overall, more CH3COO(-)

(acetate ions are

formed) to the right side, as a result of which,

according to the Le-chateliers principle, the reaction

shifts towards the left side.

Due to these shift of equilibrium to the left side, the

dissociation of CH3COOH is suppressed.

The common ion in both the above reaction is

CH3COO(-)

(acetate ion) and hence the effect

generated is termed as common ion effect.

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