ELECTRODE AND POTENTIAL

Question 1

how many half cells does 1 cell contain

Answer 1

2 half cells connected by a salt bridge

Question 2

what does a half cell contain

Answer 2

a metal and a salvation of the compound that contains the metal

Question 3

what does the half cell do

Answer 3

produce a small voltage if connected to a circuit

Question 4

how is a voltage produced

Answer 4

it will form when it is connected together and the zinc half cell will have the tendency to oxidise to the zinc ion and release electrons.

Question 5

how is the potential difference produced

Answer 5

more electrons will build up in zinc compared to copper, the potential difference will be created between them.

Question 6

how is potential difference measured

Answer 6

the zinc strip is negative and copper strip is positive, the potential difference will be measured by a high resistance voltmeter

Question 7

why do we need a high resistance voltmeter

Answer 7

to stop the current from flowing so reaction can not occur

Question 8

why is a salt bridge used

Answer 8

to connect the circuit so free moving ions can conduct the charge

Question 9

how is a salt bridge made

Answer 9

made from filter paper soaked in a salt solution - potassium nitrate the salt needs to be un reactive with the electrode and electrode solution

Question 10

what happens if the current mistakenly flows

Answer 10

the voltmeter should be removed and replaced by a bulb, the reaction will occur separately at each electrode and voltage will fall to 0 as the reactants will be used up

Question 11

what doe the solid vertical line in a convectional cell represent

Answer 11

represents a boundary between the phases of the solution

Question 12

what does the double line represent

Answer 12

the salt bridge between the two half cells

Question 13

what is written on the right side of the representation

Answer 13

the more positive half cell

Question 14

what happens is we doe not have a metal

Answer 14

we use a potassium electrode because it has a conducting surface for electron transfer

Question 15

why do we use platinum

Answer 15

it is un reactive and can conduct energy

Question 16

define standard hydrogen electrode

Answer 16

comparison electrode which all other potentials are measured against, it is assigned the potential of 0

Question 17

what are the conditions of the standard hydrogen electrode

Answer 17

hydrogen gas has pressure of 100kpa, solution has hydrogen ion at 1.0 mol dm, temperature at 298 K, no current flowing, platinum electrode

Question 18

which e cell will oxidise and which will reduce

Answer 18

the more positive will have an increasing tendency for species to reduce and act as oxidising agent, the more negative has an increasing tendency for species to oxidise and act as a reducing agent

Question 19

how to work out e cell

Answer 19

e cell= e reduction - e oxidation

Question 20

what is e cell a measure of

Answer 20

how far the from the equilibrium does the cell reaction lie, the more positive the e c ell the more likely the reaction will occur because the current can flow for reaction to occur and e cell will fall to 0 while reaction occurs

Question 21

le chateliers principle on concentration

Answer 21

increasing the concentration of reactants will increase the e cell therefore decreasing the concentration if the reactants will decrease the e cell

Question 22

le chateliers principle on temperature

Answer 22

most cells reactions will be exothermic in the spontaneous direction so a temperature rise will lead to a decrease in the e cell because the equilibrium will shift back to oppose the increase

Question 23

what happens if the e cell is positive

Answer 23

it indicates that the reaction will occur, this may be slow or not as effective. this is dependent on the activation energy, a high activation energy means a reaction will not occur.

Question 24

why can electrochemical cells be used for

Answer 24

as commercial source of electrical energy

Question 25

what are non rechargeable cells

Answer 25

not reversible e.g. lithium manganese dioxide

Question 26

what are fuel cells

Answer 26

use energy from reactions of a fuel with oxygen to create a voltage

Question 27

how can fuel cells maintain a constant voltage over time

Answer 27

they are constantly fed with fresh oxygen and hydrogen so maintain. constant acceleration of reactants, this is different to ordinary cells where the voltage drops over time as the reactant concentration will drop

Question 28

why do we use a higher temperature is cells

Answer 28

at standard conditions the rate is too low to produce an appreciable current so the higher temperature is therefore used to increase the rate, however the reaction will be exothermic so using le chateliears principle e cell would fall so higher pressure would counteract this

Question 29

what are advantages of fuel cell

Answer 29

less pollution and less CO2 because pure hydrogen will melt only water whilst hydrogen rich fuels produce only small amount of air pollutants and co2, it also has greater efficiency.

Question 30

what are some limitations to fuel cells

Answer 30

it is expensive to produce, storing the hydrogen is hard to keep safe and feasible, it is a pressured liquid and has limited life cycle of a solid absorber, due to limited lifetime it will require regular placements and disposal to have a Hugh production cost, uses toxic chemicals in its productions

Question 31

how is hydrogen stored in fuel cells

Answer 31

as a liquid under pressure, adsorbed on the surface of solid materials, absorbed with a solid material

Question 32

how is hydrogen accessed

Answer 32

it is available by the electrolysis of water but this is expensive process to be a green fuel the electricity it will need to be produced by renewable resources

Question 33

what are some advantages of ethanol

Answer 33

ethanol fuel cells are made by renewable sources in a carbon neutral way, renewable materials to produce ethanol by fermentation are abundant, ethanol is less explosive and easier to store than hydrogen.