8685348
Description
Flashcards by Anushka John, updated more than 1 year ago
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Created by Anushka John
over 7 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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