Lecture 12 Flashcards
What are polyelectrolyte solutions?
They are polymer solutions, with the polymers containing acidic or basic side groups. These polymers are called polyelectrolytes.
What does the total charge of the poly electrolytes depend on?
- pH of the solutions
- the pKa of the dissociating groups (y3ani the concentration of the polyelectrolyte)
- concentration of the background salts (which screens repulsion between charged groups)
What is the equation for pKa and the degree of dissociation? What does it mean when the pKa = pH
The equation for pKa:
pKa = pH - log([A^-]/[HA]),
The equation for the degree of dissociation:
α = [A^-1] / ([HA] +[A^-1])
For monomeric ideal acids and bases, when the pH of the solution is equal to the pKa, half of the dissociating group is in the charge state, i.e., α = 1/2 (y3ani half the acid or base has dissociated). This would apply to the polyelectrolyte of the pKa of a particular group which does not depend on the state of the neighboring groups. generally, this is not the case as repulsion between neighboring groups HINDER further dissociation.
What is the Donnan equilibrium
It is an equilibrium between a polyelectrolyte solution and salt reservoir, separated by a semi-permeable membrane
What are the conditions for thermodynamic Donnan equilibrium?
The condition for the equilibrium is simply equal electrochemical potential for both the positive and negative ions in both compartments.
The main goal of conditions is to find the concentration of ions in both compartments, which then allows for the calculation of osmotic pressure.
How do we calculate the concentration of ions in the Donnan equilibrium?
Found in notes on pages 1-2
What is the derivation for Donnan’s potential?
Found in notes on pages 2-3
What is the derivation of osmotic pressure for polyelectrolyte solutions?
Found in notes pages 4-5
