1. Conductivity

2. Types of electrolytes : There are two types of electrolytes : 1- Strong electrolytes ionized completely in the solutions,and are strong conductors of electricity. strong acids e.g, HCl, H 2 SO 4, HNO 3, HClO 4 Strong bases e.g NaOH, KOH,Ca(OH) 2,Al(OH) 3 Most of the salts are strong electrolyts like NaCl. 2- Weak electrolytes do not ionize completely in the solutions, & are weak conductors of electricity. E.g CH 3 COOH, NH 4 OH, H 3 CO 2

3. What is Conductivity? 1- Conductivity, or specifically Electrolytic Conductivity (EC), is defined as the ability of a substance to conduct electric current. 2- All substances possess conductivity to some degree, but the amount varies widely, ranging from extremely low (insulators such as benzene, glass) to very high (silver, copper, and metals in general). 3- Most industrial interest is in the conductivity measurement of liquids, which generally consists of ionic compounds dissolved in water. These solutions have conductivities approximately midway between insulators and metallic conductors. This conductivity can be measured quite easily by electronic means).

4. ELECTROLYTIC CONDUCTIVITY 1- Conductivity is a measure of capability of a media to transport charges(e- 2-The resistance of a material R is proportional to the voltage and inversely proportional to current R = V /I 3- Electrolytes are also conductors of electricity. 4- The electrical conductance of an electrolyte is due to: Concentration of ions, The greater of the concentration oions it will be the higher conductance. The size of the electrodes

5. 3 - The resistance R offered by the solution is directly proportional to the distance between the electrodes and inversely proportional to the cross –sectional area of the solution between the electrodes. The resistance R is given by : Rά l/a & R =ρ ( l /a) where ρ is the constant of proportionality known as the specific resistance. The specific resistance of the conductor is measured with ohm when its length is 1cm & and its cross section is 1cm 2

6. Equivalent conductanceMolecular conductance It is the conductance of one gram equivalent of the electrolyte dissolved in V cc of the solution. Is defined as the conductance of a volume of solution containing one mole of Solute. λ = 1000 К /N N is (Normality) μ= 1000 К /C f C is the concentration of the solution in gram equivalent per litre If C is the concentration in moles per litre ohm -1 cm -2 equiv -2 ohm -1 cm -2 mol -1 Type of CONDUCTANCE

7. 7 √ 1.The Specifice conductance of an electrolyte becomes smaller as the solution is diluted. 2.On the other hand the molecular & equivalent conductance increase with dilution until a limiting value is reached. C

8. The values of ionic conductance of anions & cations are tabulated in the following Table.

9. 9 Determination of solubilities of insoluble salts Several slightly soluble salts in water,e.g. BaSO 4,AgCl, PbS ionize in simple manner. If S is the solubility of a given salt in gram equivalent per litre & К is the specific Conductance of the saturated solution, the equivalent conductance will be Λ = 1000 К /S Therefore S =1000 К / Λ 0 Kohlrausch gave a relationship between the equivalent conductance Λo of an electrolyte.And equivalent ionic conductivity of the anions and of the cations ; Λ o = λ 0 + + λ 0 - Problem () The equivalent conductance of CH 3 COONa, HCl, NaCl at infinite dilution are 91, 426.16 & 126.45 ohm -1.cm -2.equiv -1 respectively at 25 0 C.Calculate the equivalent conductance for acetic acid.

10. إن قيمة ثابت الإتزان لا تعطي فكرة عن سرعة التفاعل وإنما تدل فقط على إتجاه التفاعل وعلـى أو أكبر، وعندما تكون أقل من الوحدة فهذا يعني 100 مدى إكتماله. وقد تصل قيمة ثابت الإتزان إلى 10 أن التفاعل يسير في إتجاه التفاعل العكسي. Weak and strong electrolytes. Arrhenius has suggested a model explaining behaviour of weak electrolytes. He assumed that for a reaction AB A + + B - the equilibrium is shifted towards products of reaction at dilute solution while as concentration increases the equilibrium shifts towards the reactants, i.e. the degree of dissociation (α )decreases as concentration increases.

11. Conductometer conductivity measuring instrument, known as “Conductometer”.

12. Effect of other Factors on Conductivity 1.concentrationa) 2.Effect of temperature : The conductivity of all electrolytes increases with increasing temperature. The rise in conductance with temperature is due to the decrease in the viscosity of the solution, increase in the speed of the ions and an increase in the degree of ionization in cases of weak electrolytes. 1. Effect of pressure :t he conductivity increases slightly with increase in pressure. The effect is mainly through changes in the viscosity of the medium, which decrease by an increase in pressure. Consequently, the equivalent conductance of the solution will increase with rise in pressure.

13. 4) Effect of solvent: In solvents of low dielectric constants, having small ionizing effect on the electrolytes, the electrostatic forces between oppositely charged ions would be appreciable and equivalent conductance will have small value. However, solvents with high dielectric constants yield more conducting solutions. 5) Viscosity of the medium: The dependence of conductance on viscosity of the medium is given by Walden’s rule, according to which the equivalent conductance of an electrolyte is inversely proportional to the viscosity of the medium, i.e.

14. Outline

15. specific conductance or conductivity (κ): It is the conductance of a material or solution occupying one cm 3 volume. It is measured in: ohm -1. cm -1 The specific conductance depends on 1-the nature of substance or the electrolyte. It increases with increase in concentration of the electrolytic solution since the number of ions per unit area increases.

18. 1- Unit of molar conductivity is A-ohm cm -1 mol -l b. ohm -1 mol c. ohm -1 cm -1 mol -l d. ohm mol -l 2- The reciprocal of resistivity is known as a. molar conductance b. specific conductance c. equivalent conductance d. permittivity

19. 3- Ω -1 cm -2 equi -1 is the unit of a. molar conductance b. specific conductance c. conductivity d. resistivity 4)-The value of equivalent conductance a.decreases with pressure. b. increases with pressure. c. decreases with dilution. d. increases with dilution.