electrode potentials

Question 1

what do simple half cells consist of?

Answer 1

• a metal that acts as an electrode
• a solution of a compound containing that metal

Question 2

how many half cells does a cell have?

Answer 2

• two half cells

Question 3

how do the half cells have to be connected

Answer 3

• via a salt bridge

Question 4

why does a voltage form when you connect the two half cells into a circuit?

Answer 4

• one half cell will have more of a tendency to oxidise
• more electrons will build up, creating a potential difference between the two electrodes

Question 5

why do we need to use a high resistance voltmeter?

Answer 5

• to stop current from flowing in the circuit
• to measure maximum possible E

Question 6

how does the salt bridge work?

Answer 6

• usually made from a piece of filter paper soaked in a salt solution
• salt should be unreactive with the electrodes and electrode solution
• used to connect the circuit

Question 7

why is a wire not used in the circuit?

Answer 7

• a metal wire would set up its own electrode system with the solutions

Question 8

what are the specific rules for conventional cell representation?

Answer 8

• the half cell with most negative potential goes on the left
• the most oxidised species from each half cell goes next to the salt bridge
• a salt bridge is shown using a double line
• always include state symbols

Question 9

for systems that do not include metals what happens?

Answer 9

• a platinum electrode must be used and included in the cell diagram
• it provides a conducting surface for electron transfer
• it is unreactive and can conduct electricity

Question 10

what can standard electrode potentials be used for

Answer 10

• to predict reaction feasibility under standard conditions

Question 11

how can we predict feasibility

Answer 11

• identify which is being oxidised with most negative E value
• take the oxidised equation and reverse it
• combine these 2 equations to form the feasible reaction
• compare with question to see

Question 12

if a reaction is feasible, what will the E0 value be

Answer 12

positive

Question 13

what are batteries

Answer 13

• electrochemical cells that come in 2 main forms

Question 14

give properties of rechargeable batteries

Answer 14

• expensive
• reversible and can last longer in the long term

Question 15

what are lithium batteries used in

Answer 15

• power tools
• tablets
• mobile phones

Question 16

what components do mobile phones have with a lithium ion cell

Answer 16

• Electrode A - lithium cobalt oxide
• Electrode B - graphite
• Electrolyte - lithium salt dissolved in an organic solvent

Question 17

what is the electrolyte

Answer 17

• part of battery that acts as a conductive pathway for ions to move from one electrode to another

Question 18

what does the negative electrode inside a battery do

Answer 18

• produces electrons

Question 19

how do rechargeable batteries work

Answer 19

• plugging them into supply a current
• current forces electrons to flow in opposite way
• reverse the overall discharge equation to show a battery recharging