Electrode Potentials

Question 1

what is a half cell?

Answer 1

one half of an electrochemical cell

Question 2

what is a half cell made of?

Answer 2

metal dipped in its ions or a platinum electrode with aqueous ions

Question 3

what condition is needed if a half cell has 2 aqueous ions?
give an example

Answer 3

• an inert but electrically conductive electrode must be used
• e.g. platinum

Question 4

how is an electrochemical cell created?

Answer 4

• joining 2 different half cells together, joined by a wire, voltmeter and a salt bridge
• one side undergoes reduction + the other undergoes oxidation

Question 5

what is a voltmeter used for in electrochemical cells?

Answer 5

used to measure voltage in between 2 cells

Question 6

describe the flow of electrons in an electrochemical cell

Answer 6

electrons flow from a more reactive metal to a less reactive one

Question 7

what is EMF/Ecell?

Answer 7

voltage between 2 half cells

Question 8

what happens to the oxidation electrode?

Answer 8

will become thinner as more Xⁿ⁺ positive ions are produced to make the electrons

Question 9

what happens to the reduction electrode?

Answer 9

will become thicker as positive ions receive the electrons to produce metal atoms

Question 10

what is the purpose of the salt bridge?

Answer 10

free ions flow through to complete the circuit

Question 11

what are electrode potentials measure in?

Answer 11

volts

Question 12

what do electrode potentials tell us?

Answer 12

how easily half cell oxidised

Question 13

which half cell will undergo oxidation?

Answer 13

most negative

Question 14

which half cell will undergo reduction?

Answer 14

most positive

Question 15

what is the standard hydrogen electrode (SHE)? why is this needed?

Answer 15

• used as a reference to measure standard electrode potentials
• has an electrode potential of 0.00V
• electrode potentials cant be measured on their own so need to be measured against a standard half cell

Question 16

how can a concentration of 1 mol dm^-3 of H⁺ be obtained?

Answer 16

1 mol dm^-3 of HCl or 0.5 moles of H₂SO₄

Question 17

does a more positive electrode potential represent an oxidising agent or a reducing agent?

Answer 17

oxidising agent

Question 18

does a more negative electrode potential represent an oxidising agent or a reducing agent?

Answer 18

reducing agent

Question 19

how is the standard electrode potential of a cell calculated?

Answer 19

Ereduced - Eoxidised

Question 20

in cell notation, where does the most negative half cell go?

Answer 20

to the left of the salt bridge

Question 21

if electrode potential value is positive, is the reaction feasible or not?

Answer 21

feasible

Question 22

what is an advantage of using non rechargeable batteries?

Answer 22

cheaper

Question 23

what is an advantage of using rechargeable batteries?

Answer 23

reversible reaction so last longer

Question 24

what is the electrolyte of a battery?

Answer 24

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

Question 25

how is electricity generated in a fuel cell?

Answer 25

electricity generated by a continuous external supply of chemical

Question 26

outline the alkaline hydrogen-oxygen fuel cell reaction

Answer 26

1. hydrogen fed in, reactions with OH- ions in solutions
   2H2g + O2g -> 2H2Og
2. e produced travel through a platinum electrode
3. flow of e used to power something
4. oxygen fed in + reacts with water + the 4e in 1 to make OH- ions
   O2g + 2H2Ol + 4e -> 4OH-
5. e flow to the positive electrode which is made from platinum
6. electrolyte is made from KOH solution -> carries the OH- ions from cathode to anode
7. e flow from neg electrode which is made from platinum
8. water released to surroundings
9. OH- produced in 4. are carried toward the anode via the electrolyte