Electrode potentials and electrochemical cells

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A level Chemistry Flashcards on Electrode potentials and electrochemical cells, created by Anushka John on 04/26/2017.
Anushka John
Flashcards by Anushka John, updated more than 1 year ago
Anushka John
Created by Anushka John over 5 years ago
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Question Answer
How is an electrochemical cell set up? * has 2 half cells * each cell has a metal rod, acting as an electrode, submerged in a solution of its own ions * the two half cells are connected by a salt bridge (which allow the transfer of ions) *will produce a voltage if connected to a circuit
Why does a voltage form? * The anode (eg zinc) has more of a tendency to oxide to the Zn 2+ ion, and release electrons than the copper electrode * so moreelectrons build up on the zinc electrode *forming a ptoential difference across the electrodes * the potential difference is measured with a high resistance voltmeter
Why is a high resistance voltmeter used? * stops current flowing in the circuit * stops reaction from occuring *so can measure the maximum potential differencr
Why is the salt bridge used? * to complete the circuit *the free moving ions conduct the charge * the salt should be unreactive with the electrode and electrode solutions *a wire is not used because the metal wire would set up its own equilibrium system
How is a salt bridge usually made? By soaking some filter paper in a salt solution
What would happen if the current was allowed to flow? *electrons would travel from the zinc to the copper electrode * zinc (as it becomes Zn-) would get used up and copper (as Cu2+ gain electrons and become Cu) would build up * voltage would drop to 0 as zinc gets used up * the most +ve (where electrons are used up) undergoes reduction * the most -ve (electrons given off) undergoes oxidation
What are the rules for writing a cell diagram? * vertical line = phase change * diff species but no phase change = comma * double vertical line = salt bridge * voltage produced is written * highest oxidation states are closest to the salt bridge * more positive half cell on right
What do you do if the system does not include a metal, but instead a gas? Use a Pt electrode must be inc in cell diagram (at ends) provides a conducting surface for electron transfer * Pt can be used as it is UNREACTIVE and CONDUCTS ELECTRICTY
What if a half equation contains balancing coefficients and H+'s and electrons. Do you include them in the cell diagram? No they can be left out
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