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3.7 standard.pdfThis internal will be completed in the last 3 weeks of term 1 and will be due on the last day of term.
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Learn
The following content is from Yr12. If you do not remember how to do one of these points then go to my yr 12 redox page.
LEO the lion goes GER
Oxidation numbers
Balancing of equations (half and full)
Oxidants and reductants
Colours of species.
We must know the year 12 content in order to get an achieved, merit or excellence at year 13.
Electrochemical cells
Electrochemical cells
In year 13 we are able to apply the year 12 knowledge in an experimental context.
An electrochemical cell is 2 beakers where oxidation will occur in one beaker and reduction will occur in the other.
OxidAtion occurs at the Anode.
ReduCtion occurs at the Cathode.
Cell Diagrams
Cell Diagrams
Instead of drawing out a picture we call do a shorthand diagram. Things to remember:
Always include the states (g, aq, s)
/ in between different states
, in between the same state.
// to separate the anode and cathode, indicating the salt bridge.
Cathode pair is written on the right.
Salt bridge
This is a connecting tissue soaked in usually KNO3 (different to the picture). The purpose of the salt bridge is to maintain electrical neutrality. The anode is losing negative electrons so the negative nitrate goes to the anode to balance the charge. Likewise the positive potassium goes to the cathode to balance out the increase in negative electrons.
Standard reduction potentials
Standard reduction potentials
You will always be provided with this data on the right.
The higher the number, the more likely it is to be reduced. This is how you know which half equation is being reduced and which one is being oxidised.
We can then work out the E of the cell which is the voltage the reaction should create if done under standard conditions.
Side note that standard conditions are the following:
25 degrees Celsius
1 atmospheric pressure (atm)
1molL-1 concentrations
Finally, if the E of the cell is positive then the reaction will be spontaneous. If it is negative then the reaction is not spontaneous
Electrolytic Cells
Electrolytic Cells
The majority of the knowledge that we learnt with regard to electrochemical cells and redox in general is the same.
One of the main differences between an electrochemical and and electrolytic is that the electrolytic is in one beaker. It is a solution containing a cation and anion which requires two electrodes to be used as well.
The other big difference is that for an electrochemical cell we use the E values to work out which chemical is being oxidized and reduced. For an electrolytic cell, it is much more simple:
The Anion is attracted to the Anode (where oxidation occurs).
The Cation is attracted to the Cathode (where reduction occurs).
An extra detail to add in when comparing and contrasting these two cells is relating the spontaneity to the power. If it is spontaneous then the reaction will produce an electric charge. If it is not spontaneous then the reaction will require an electrical charge in order to make the reaction happen.
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