PAG 08 - Electrochemical Cells Flashcards
(13 cards)
What must a half cell contain
An element in 2 oxidation states
Define oxidation and reduction
Oxidation = loss of electrons
Reduction = gain of electrons
Why must metal electrodes be cleaned with sandpaper before creating electrochemical cell
To remove any metal oxide that has formed on surface and improve electrical conductivity
Describe movement of electrons in an electrochemical cell
Electrons flow through wire from positive electrode to negative electrode
In an standard Zn/Zn^2+ cell, what’s the role of potassium nitrate solution
Potassium nitrate is used to saturate a piece of filter paper so that it can be used as a salt bridge
Why’s a salt bridge used in an electrochemical cell
To maintain the charge balance and complete the circuit.
This is because negative electrons are moving from one half cell to another. Without the salt bridge, positive charge would build up in the half cell containing the anode and negative charge would build up in the half cell containing the cathode. This would cause the reaction to stop.
Why must an inert salt be used in salt bridge
So that salt doesn’t react with solutions and alter their concs.
If a reactive salt was used, the cell potential would change
What moves across salt bridge
Ions
In an electrochemical cell, each metal electrode is placed in a solution containing what
It’s ions
E.g. solid copper is placed in a solution of copper(II) sulfate
Standard conditions are often used when investigating electrochemical cells. What are standard conditions
1 mol dm^-3 solutions
298K
1 atm
After setting up an electrochemical cell, reading on voltmeter is negative. What should be done
Switch connection of wires so electrodes are the right way round
What’s the formula from electromotive force (EMF)
EMF = Er - El
Er = right hand cell = where reduction occurs
El = left hand cell = where oxidation occurs
For a reaction to be thermodynamically feasible, what must value of EMF be
Positive
