Donnan membane effect

2. Presented to-
Dr. Md. Shahadat Hossain
Associate Professor
Department of Chemistry
Comilla University
Presented By-
Abdulla Al Noman Mieazi
Id-119140030
Session-2018-19
Department of Chemistry
Comilla University
Presentation on-The Donnan-Membrane Effect
𝑹−

3. DEFINATION-
If diffusible solutes are separated by a membrane that is
freely permeable to water and electrolytes but totally
impermeable to one species of ion, the diffusible solutes
become unequally distributed between the two
compartments.
• Discovered by Fredrick Donnan 1911.
The Donnan-Membrane Effect

4. Donnan-Membrane Equilibrium-
The Donnan membrane equilibrium is the state of balance that is reached after the
Donnan membrane effect has occurred, where the unequal distribution of ions is
balanced by the diffusion of ions across the membrane, resulting in equal osmotic
pressure but unequal concentrations of non-diffusible ions.

5. Donnan-Membrane Equilibrium-

6. Donnan-Membrane Equilibrium-

7. Donnan-Membrane Equilibrium-

8. Donnan-Membrane Equilibrium-

9. Derive an equation for Donnan Membrane Equilibrium-
According to thermodynamics, at equilibrium the chemical potential of
identical species present on both the sides of membrane must be
same.The chemical potential (μ) is given by equation,
μ = μ𝟎 + RT Ina
Where μ𝟎 is the standard chemical potential and a is the activity of the
species.
μNaCI(1) = μNaCI(2)
μ𝟎
NaCl(1) + 𝑹𝑻 Ina NaCl(1) = μ𝟎
NaCl(2) + 𝑹𝑻 Ina NaCl(2)
0r, a NaCl(1) = a NaCl (2)
So, 𝒂𝑵𝒂(𝟏)× 𝒂𝑪𝒍(𝟏)= 𝒂𝑵𝒂(𝟐)× 𝒂𝑪𝒍(𝟐)
Donnan-Membrane Equilibrium-

10. If the solution is very dilute, the activities can be replaced by
molar concentration
So, [Na(l)][Cl(l)] = [Na(2)][Cl(2)]
Substituting the respective concentrations,
(𝑪𝟏 − X) (𝑪𝟏 −X) = (C₂ + X) (X)
𝒐𝒓, 𝑪𝟏
𝟐
− 𝟐𝑿𝑪𝟏+𝑿𝟐=X𝑪𝟐 + 𝑿𝟐
𝒐𝒓, 𝑪𝟏
𝟐
− 𝟐𝑿𝑪𝟏= X𝑪𝟐
𝒐𝒓, 𝑪𝟏
𝟐
= X(𝑪𝟐+ 𝟐𝑪𝟏)
𝒐𝒓, 𝑿
𝑪𝟏
=
𝑪𝟏
(𝑪𝟐+ 𝟐𝑪𝟏)
𝒐𝒓, 𝑪𝟏
𝟐
=X(𝑪𝟐 + 𝟐𝑪𝟏) 𝒔𝒐,
𝑿
𝑪𝟏
=
𝑪𝟏
(𝑪𝟐+𝟐𝑪𝟏)
Donnan-Membrane Equilibrium-

11. The term
𝑿
𝑪𝟏
is the fraction of total NaCl that diffuses across the
membrane (i.e. from LHS to RHS). To have the concentration of NaCl
same on both the sides of membrane, the condition to be
maintained is
𝑿
𝑪𝟏
=
𝟏
𝟐
The concentration differences due to Donnan
equilibrium are useful to account for the swelling of certain gels for
difficulties in osmotic pressure measurements on protein solutions,
for the establishment of potential differences across membranes etc.
Donnan-Membrane Equilibrium-

12. Significance of Donnan Equilibrium-
Biological systems
 The distribution of ions between RBC and
surrounding plasma
Artificial kidney
Tanning of leather
Dyeing of animal fibres by acid dyes

13. Thank You Everyone