Presentation on theme: "STANDARD REDUCTION POTENTIAL. STANDARD REDUCTION (ELECTRODE) POTENTIAL (E O ) Is a measurement that indicates how easily a half cell undergoes reduction."— Presentation transcript:
STANDARD REDUCTION (ELECTRODE) POTENTIAL (E O ) Is a measurement that indicates how easily a half cell undergoes reduction. Indicates how much voltage will a half cell produce. This is an experimentally determined value
The standard hydrogen electrode The half-cell is connected to a hydrogen half cell: Pt (s) / H 2(g), H + (aq) under standard conditions. Standard conditions are: 1.Concentration of all aqueous reactants are 1molL -1. 2.Metals are pure metals. 3.Gas pressure is 101.3kPa (at sea level) 4.Temperature is 298K (25 o C)
For example: Mg has a greater tendency to build up ions. The position of Mg’s equilibrium will be more to the left than hydrogen.
The magnesium has the greater amount of negativeness - the voltmeter records that as negative. The platinum of the hydrogen electrode isn't as negative - it is relatively more positive. The voltmeter records it as positive. The voltage measured would be 2.37 volts and the voltmeter would show the magnesium as the negative electrode and the hydrogen electrode as being positive. Therefore, E o (Mg 2+ /Mg) =-2.37 V
Copper forms its ions less readily than hydrogen does. Of the two equilibria the hydrogen one lies further to the left. That means that there will be less build-up of electrons on the copper than there is on the platinum of the hydrogen electrode. The copper is the more positive (less negative) electrode. The voltmeter will show the hydrogen electrode as the negative one and the copper electrode as positive. Therefore, E o (Cu2+/Cu) =0.34 V
Reduction potential values equilibriumE° (volts) -3.03 -2.92 -2.87 -2.71 -2.37 -1.66 -0.76 -0.44 -0.13 0 +0.34 +0.80 +1.50 The more positive the E o, the: The greater the tendency to reduce The stronger the oxidant. Greater the tendency to accept electrons The more negative the E o, the: The greater the tendency to oxidise The stronger the reductant. Greater the tendency to lose electrons
What is E o cell E o cell is the voltage difference between 2 cells. It is th energy that pushes and pulls electrons Aka emf or electromotive force.
Calculating E o cell Example : Calculate the E o cell for : Al(s)|Al 3 +(aq)|Cu(s)|Cu 2+ (aq), given E o (Al 3+ /Al) =-1.66 V and E o (Cu 2+ /Cu) =0.34 V 1.State the positive electrode. 2.Name the electrode where reduction takes place. 6 3.Calculate voltage. 4.Write cell reaction.