SS2 Third Term Chemistry Lesson Note – Electrochemical Cell

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WEEK 3

TOPIC:   ELECTROCHEMICAL CELL: 

1. Standard electrode potential
2. Drawing of cell diagram and writing cell notation
3. M.F of cells
4. Application of electrochemical cells.

PERIOD 1: STANDARD ELECTRODE POTENTIAL,

ELECTROCHEMICAL CELLS

Electrochemical cell is a device that converts chemical energy to electrical energy.

SOME PARAMETERS ASSOCIATED WITH ELECTROCHEMICAL CELL

1. Standard hydrogen electrode: The standard hydrogen electrode consists of hydrogen gas at 25^oC and one atmospheric pressure bubbling around an inert platinum electrode in contact with one-molar solution of hydrogen ions i.e., /H_2(g) system. It is the reference standard by which the standard electrode potential of a metal ions/metal system is measured against. The standard hydrogen electrode potential has been given assigned a value of zero.
2. 2. Standard electrode potential (E^o): Standard electrode potential of a metal ions/metal system is the potential difference set up between the metal and one-molar solution of its ions at 25^oC (arbitrarily taking the standard electrode potential of hydrogen ions/hydrogen gas system as zero volts.
3. Salt bridge: It is a piece of paper soaked in potassium chloride solution or ammonium chloride solution. Its functions are to complete the electric circuit and enable the movement of ions from one half-cell to another so as to maintain electrical neutrality in the solution.

MEASUREMENT OF STANDARD ELECTRODE POTENTIAL

In measuring the standard electrode potential of particular metal ion/metal system, the half-cell of the metal ions/metal system e.g. /Zn_(s) is connected to that of hydrogen ions/hydrogen gas system by a salt bridge. The reading shown on the voltammeter is the electromotive force or the e.m.f of the cell. Since the standard electrode potential of hydrogen ions/hydrogen gas system is assigned the value zero, the value obtained in the standard electrode potential of the metal system.

The sign of the standard electrode potential of a given metal systems dependent of the direction of the electron flow in the cell. If electron flows from hydrogen ions /hydrogen gas system to the metal ions/metal system, the standard electrode potential of that metal system is assigned a negative value. If the flow of electron is in the reverse direction, it is assigned a positive value. For example, the standard electrode potential of zinc ions/zinc meal system is -0.76v because during the measurement, the flow electrons is from hydrogen system to zinc system. E^o /Zn_(s) = -0.76v

E^o Cu²⁺_(aq)/Cu_(s)  =  +0.34

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