Ionic equilibrium

Ionic equilibrium

1. Outline Ionic Equillibrium Common Ion Effect Factors Of Common Ion Effect solubility product Applications Of Solubility Product

2. Ionic Equillibrium

3. IONIC EQUILIBRIUM INTRODUCTION 1. Equilibrium is the state at which the concentration of reactants and products do not change with time . 2. Equilibrium may also be defined as state of process in which properties like temperature,colour,pressure , Concentration of the system do not show any change with time .

4. TYPES OF EQUILIBRIUM PHYSICAL EQUILIBRIUM — If the opposing processes involves only physical changes(melting of ice water)the equilibrium is called physical equilibrium . CHEMICAL EQUILIBRIUM — If opposing processes involves chemical changes(the reaction between H 2 and I 2 )the equilibrium is called chemical equilibrium

5. TERMS USED IN IONIC EQUILIBRIUM ELECTROLYTE --- An electrolyte may be defined as substance which either in molten state or in aqueous solution can conduct electricity.Acids ,bases and salts are mostly electrolytes.There are two types of electrolytes.

6. TYPES OF ELECTROLYTES STRONG ELECTROLYTES-- THE ELECTROLYTES WHICH ARE ALMOST COMPLETELY IONIZED IN Aq. SOLUTION. Eg.H 2 SO 4 ,HCl WEAK ELECTROLYTES — THE ELECTROLYTES WHICH ARE IONIZED TO SMALL EXTENT IN Aq. SOLUTION . Eg.CH 3 COOH,NH 4 OH

7. Ionization of an Electrolyte in aqueous solution The molecules of some compounds, when dissolved in water gets decomposed in two types of charged particles called ions.The ions which carry positive charge are called cations . The ions which carry negetive charge are called Anions.Initially, very few molecules get decomposed into ions. Gradually, the concentration of ions increases.When the concentration of ions becomes too high, the ions reunite to form molecules again. At certain stage, Equilibrium is set up.This state of process is called ionic equilibrium.

8. C.M Gulberg and P. Waag in 1864 studied a lot of reversible reactions and gave a generalization Rate of a chemical reaction is proportional to the product of Molar concentration raised to a power equal To the num of times, the particular substance appear in stoichiometric Equation. This is called law of chemical equilibrium.

9. Kc is called equilibrium constant . Symbol of Kc is used when concentration of A, B, C and D are taken in moles/dm-3 Kc is product of equilibrium concentration of product divided by the product of equal concentration of reactants.

10. Each concentration term is raised to the power equal to The co-efficient of the substance in the balanced Equation. aA + bB cC +dD Kc = [C] [D] [A] [B] Also called law of chemical equilibrium.

11. According to Arhenius Theory Of dissociation, an electrolyte Dissociates into ions in water solution. These ions are in a state of Equillibrium with the undissociates molecules. This equilibrium is called ionic equilibrium. Ostwald noted that law of mass action can be applied to the ionic equilibrium as in the case of chemical equilibria.

12. A binary electrolyte AB dissociates in sol. And form A and B AB A

13. Common Ion Effect

14. The reduction of the degree of a salt By the addition of a common ion is called common ion effect. Example; Saturated solution of silver chloride In other words The phenomenon of lowering the degree of ionization of a weak electrolyte by adding a solution of strong electrolyte having a common ion is common ion effect.

15. Knowledge of common ion effect is very useful in Analytical chemistry It is frequently applied in qualitative analysis. An electrolyte is precipitated only when the concentration of its ion exceed the solubility product.

16. Example: What would happen if we sodium chloride into the Solution? A salt will be less soluble if one of its constituents ions is already present in the solution.

17. Factors O f C ommon I on Effects.

18. Degree Of Dissociation: The fraction of the amount of the electrolyte in Solution present as free ions is called degree of dissociation.

19. 1- Nature Of Solute: Nature of solute is the chief factor which determines Its degree of dissociation in solute. Strong acid and bases, and the salt obtained by their interaction are almost completely dissociated in solution

20. Weak acids and bases and their salts are not completely dissociated or feebly dissociated in solution.

21. Nature Of The Solvent The nature of solvent affects dissociation to a marked degree. It weakens the electrostatic forces of attraction between the two ions and separate them. This effect of the solvent is measured by its “ dielectric constant” .

22. Dielectric constant of a solvent may be defined as its capacity To weaken the force of attraction between the electrical charges Immersed in solvent. The higher the value of the dielectric constant the greater is the dissociation of the electrolyte dissolved in it.

23. Concentration The extent of dissociation of an electrolyte is inversely Proportional to the concentration of its solution. The less concentrated the solution, the greater will be the dissociation of the electrolyte

24. Due to the fact that in a dilute solution the ratio of solvent molecules to the solute molecules Is larger and the greater number of solvent molecules will separate more molecules Of the solute into ions.

25. Temperature The dissociation of an electrolyte in solution also depends on temperature. The higher the temperature greater is the dissociation.

26. At high temperature the increased molecular velocities overcome the Forces of attraction between the ions and consequently the dissociation Is great.

27. S olubility Product

28. A specific type of chemical equilibrium in which a solid salt dissolves into its ions in a solution is called solubility product. E xample HgCl (s) Hg(aq) + 2Cl (aq) Ksp = [Hg2][Cl] = 1.2x 10

29. When an ionic solid substance dissolves in water, it dissociates to give separate Cations and anions. Concentration of the ions in solution increases, they collide and reforms the solid phase.

30. Ultimately a dynamic equilibrium is established between the solid phase and the cations and anions in solution. Ksp = product of the concentration of ions in the saturated solution at a given temperature is constant. Also called solubility product principle.

31. Numerical problems Case 1 : We can calculate the solubility of an ionic compound if the Ksp value is given. Calculation of solubility from Ksp:

32. Case 2 : Whether precipitation will occur on mixing solution: When two reacting solution are mixed, calculate the concentration of each ion in the solution in which precipitation is produced. The ionic product Q is then calculated. We know that Ksp is the ionic product when the ions are in contact with the solid substance.

33. Precipitation will take place if Q>Ksp No precipitation will take place if Q<Ksp

34. Applications of Solubility Product.

35. Precipitation reaction are used to identify cations present in an unknown mixture of salts. The ion product and Ksp: The solubility product (Ksp) of an insoluble substance is the product of the concentration of its ion at equilibrium.

36. Ion product is the product of actual concentration of ions which may or may not be in equilibrium with the solids. Q > Ksp = precipitation will occur Q < Ksp = no precipitation will occur. Q = Ksp, then solution is saturated.

37. The scheme of Qualitative Analysis is based on the principle Of selective Precipitation.