electrochemical cells

Question 1

what is a voltaic cell?

Answer 1

a type of electrochemical cell which converts chemical energy into electrical energy

Question 2

what is a half cell?

Answer 2

a cell which contains the chemical species present in a redox half equation

Question 3

how is a voltaic cell made?

Answer 3

the connection of two half cells, allowing electrons to flow

Question 4

why must the chemicals be kept apart in a voltaic cell?

Answer 4

if allowed to mix, electrons would flow in an uncontrolled way and heat energy would be released instead of electrical energy

Question 5

how is a metal half cell made?

Answer 5

metal rod dipped in solution of its aq metal ioon

Question 6

describe the electron flow in a half cell compared to an electrochemical cell

Answer 6

half cell = no net transfer of electrons in/out of metal

electrochemical = direction of electron flow depends upon relative tendency of each electrode to release electrons

Question 7

what is an ion half cell?

Answer 7

contains ions of same element in different oxidation state
eg iron II and iron III ions

Question 8

how is an ion half cell made?

Answer 8

as there is no metal to transport electrons, an inert metal electrode made of platinum is in solution
- allows electrons in/out of cell

Question 9

which is the negative electrode?

Answer 9

the electrode with more reactive metal
- loses electrons
- is oxidised

Question 10

which is the positive electrode?

Answer 10

the electrode with the less reactive metal
- gains electrons
- is reduced

Question 11

define ‘standard electrode potential’

Answer 11

the tendency for a species to be reduced and gain electrons

Question 12

describe what is meant by standard electrode potential?

Answer 12

electrode multi force of a half cell connected to a standard hydrogen half cell under standard conditions

Question 13

what is the standard electrode potential of hydrogen?

Answer 13

0 V

Question 14

describe how a standard electrode potential measured

Answer 14

connect half cell to standard electrode

connect 2 electrodes by a wire to allow flow of electrons

connect solutions with a salt bridge (allows more ions to flow)

Question 15

describe the salt bridge

Answer 15

allows ions to flow

contains concentrated solution of electrolyte that doesn’t react with either solution

eg filter paper soaked in KNO3 aq

Question 16

what does a more negative standard electrode potential tell us?

Answer 16

greater tendency to lose electrons: undergoes oxidation

less likely to gain electrons and undergo reduction

Question 17

what does a more positive standard electrode potential tell us?

Answer 17

greater tendency to gain electrons: undergoes reduction

less likely to lose electrons and undergo oxidation

Question 18

what standard electrode potential do metals usually have?

Answer 18

negative
- loss of electrons
- oxidation

Question 19

what is the relationship between reactivity and standard electrode potential?

Answer 19

more negative = more reactive in losing electrons

more positive = more reactive in gaining electrons

Question 20

describe how you would set up cells to measure cell potentials

Answer 20

prepare 2 standard half cells
- metal: must be 1moldm-3
- ion: both metal ions must have same conc, must be an inert electrode
- gases: gas must be 100kPa, solution conc 1moldm-3, inert electrode

connect metal electrodes of half cells to voltmeter using wires

add a salt bridge & connect the solutions

record standard cell potential from voltmeter

Question 21

how is standard cell potential calculated from standard electrode potentials?

Answer 21

electrode potential of positive electrode - electrode potential of negative electrode

Question 22

in an electrochemical cell, what are the charge carriers in the wire & salt bridge?

Answer 22

wire = electrons
salt bridge = ions

Question 23

state the standard conditions used for electrochemical cells

Answer 23

gas pressure → 100kPa
temperature → 298 K/25°C
concentration → 1 mol dm⁻³