Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Electrical Resistance and Electrical Conductance: Ohm’s law gives exact relationship between the resistance, the current and voltage. "If to the ends of a conductor a voltage "E" is applied and a current "I" flows through it, then the resistance "R" of the conductor: (written Ω) All electrolytic solution like metallic conductors obey ohm’s law. Conductance: Is the property of the conductor "metallic as well as electrolytic" which facilitates the flow of electricity through it. conductance: the reciprocal of the electrical resistance is called the conductance (c), thus: (Ω-1), or mol or, Siemens (s). Specific resistance & specific conductance: The resistance (R) of a conductor is: 1- Directly proportional to its length (l) and, 2- Inversely proportional to its area of cross-section (a) Specific resistance : r : is a constant of proportionality, called specific resistance or (resistivity). Its value depends upon the material of the conductor. Specific conductance: "the reciprocal of specific resistance is known as specific conductance or conductivity. It is denoted by ( ). Thus, if is the specific conductance and C is the conductance of the solution, then: specific conductance ( ): is defined as the conductance of a solution of definite dilution. Enclosed in a cell having two electrodes of unit area separated by 1cm length and 1cm2 as the area of cross-section as shown in Fig. isthe conductance of 1cm3 of the solution of the electrolyte. Cell constant: Cell constant = Where (l) is the distance between the electrodes of the cell, and (a) is the surface area of the electrode. Thus cell constant may be obtained by measuring l & a. Alternatively, this may be obtained as follows with the help of the following equation. Equivalent conductance and Molar conductance : Equivalent conductance: Is the conductance of all ions produced from 1g.eq. of the electrolyte dissolved in Vcm3 of the solution when the distance between the electrodes is so large that whole of the solution is contained between them. It is represented by eq. The equivalent conductance eq of a solution is calculated from the specific conductance . The relationship between Ʌ & maybe obtained as follows: Consider a rectangular vessel with its two opposite walls 1cm a part and made of some metal sheets so that they act as the electrodes. Case I : Suppose 1cm3 of the solution containing 1g.eq. of the electrolyte is taken in the vessel The conductance c of this solution will be its specific conductance Further 1cm3 of the solution taken contains 1g.eq. of the electrolyte, the conductance c of the solution will be its equivalent conductance eq. (by definition) → c =eq. Thus , when 1cm3 of the solution containing 1g.eq. of the electrolyte is considered : eq= Case II : Suppose 4cm3 of the solution containing 1g.eq. of the electrolyte is taken. The conductance C of the solution will be still equal to its equivalent conductance eq at this dilution, but now there will be 4 cubes each of volume 1cm3 as shown in Fig. For each 1cm3 of the solution So that the total conductance C of the solution, i.e., equivalent conductance eq is 4 times the specific conductance . equivalent conductance = specific conductance * V eq Where V is the volume in cm3 containing 1g.eq. of the electrolyte In terms of concentration, if the solution has a concentration of C g.eq. /l, i.e., c g.eq’s. are present in 1000 cm3 of the solution then the volume of the solution containing 1g.eq. will be : eq Molar conductance : Is the conductance of all the ions produced from 1mole of the electrolyte dissolved in V cm3 of the solution when the electrodes are 1cm apart and the area of the electrodes is so large that the whole of the solution is contained between them. It is usually represented by m Molar conductance m is related to the specific conductance as follows : Molar conductance = specific conductance * volume in cm3 containing 1mol of the electrolyte m m = ohm-1 . cm2 . mol-1 = S cm2 mol-1 = Ω-1 cm2 mol-1 or or