electrochemistry and cells

Question 1

standard conditions for measuring electrode potential (3)

Answer 1

• conc. of solutions = 1.0 mol/dm3
• 298K
• 100kpa / 1atm

Question 2

standard cell for comparison (primary)

- electrode used

Answer 2

hydrogen cell

- platinum

Question 3

metal dipping into solution =

Answer 3

half cell

Question 4

if eq. lies to the left, charge will be … due to … making the potential …

Answer 4

negative
due to build up of electrons on metal
negative

Question 5

if eq. lies to the right, charge will be … due to … making the potential … ??

Answer 5

positive
as electrons used up to form the metal
positive

Question 6

more reactive metals tend to have ….. potentials

Answer 6

negative

Question 7

positive potential = … hand electrode = ….

Answer 7

right

cathode

Question 8

emf of cell =

Answer 8

E right - E left

Question 9

secondary standard

Answer 9

one which has been calibrated against primary standard

Question 10

anode…

Answer 10

oxidation

negative

Question 11

which way do reduction reactions go

Answer 11

left to right

Question 12

which what type of reaction is the more negative V

Answer 12

oxidation

Question 13

which way do oxidation reactions go

Answer 13

right to left

Question 14

what is always needed for fuel cells?

- what can be used?

Answer 14

• oxygen!!

- hydrogen/alternatives

Question 15

set up used to investigate potential of an electrode

Answer 15

• use standard hydrogen electrode

- salt bridge - potassium nitrate

Question 16

for a positive potential difference, electrons moe from…. to …

Answer 16

left

right

Question 17

zinc-carbon cell - features

Answer 17

• cheap
• non-rechargable
• fairly short life

Question 18

alkaline cell features

Answer 18

• higher cost then zinc-carbon

- longer life “

Question 19

lithium ion cell features

Answer 19

• rechargable

- used in phones, computers etc.

Question 20

lead acid battery features

Answer 20

• made of 6 cells

- used in cars

Question 21

how are fuel cells different to other cells?

Answer 21

continuous supply of chemicals into the cell, so neither run out or need recharging

Question 22

fuel =

Answer 22

something that reacts with oxygen to release energy

Question 23

most common methods of producing H2

Answer 23

• electrolysis of sea water

- methane + steam

Question 24

benefits of hydrogen-oxygen fuel cells (3)

Answer 24

• only waste product is H2O
• efficient
• dot need recharging

Question 25

cons of hydrogen-oxygen fuel cells (4)

Answer 25

• needs constant fuel supply
• hydrogen = flammable and expensive
• H2 production usually involves fossil fuels
• high cost of cell

Question 26

voltaic cell =

Answer 26

connecting 2 half cells together

Question 27

why must 2 different half cell species be kept separate?

Answer 27

otherwise electrons would flow in uncontrolled way and heat energy produced instead of electrical

Question 28

electrode with MORE reactive metal will … electrons and is ….. making it the ….

Answer 28

loose
negative
anode

Question 29

standard electrode potential =

Answer 29

tendency to be reduced and gain electrons

Question 30

limitations of predictions using standard electrode potentials (3)

Answer 30

• rate of reaction - large activation energy - doesn’t give indication of rate
• concentration - will affect, not all cells have 1.0 mol/dm3
• conditions may vary

Question 31

what are electrodess in hydrogen fuel cel made from

Answer 31

platinum

Question 32

overall reaction for the hydrogen-oxygen fuel cell

Answer 32

2H2(g) + O2(g) → 2H2O(g)

Question 33

what happens to the metal in a cell with the MORE POSATIVE electrode potential

Answer 33

is REDUCED and GAINS electrons

Question 34

positive electrode is one with

Answer 34

lowest standard electrode potential

Question 35

standard cell potential (eq)

Answer 35

Eθcell = Eθright half-cell − Eθleft half-cell

Question 36

why is a high resistance voltmeter used to measure electrochemical cells?

Answer 36

• prevents current flowing through circuit
• if current flowed, reactants would be used up at both electrodes
• E cell would then decrease

Question 37

the more negative the E°, the further the eq lies to the …

Answer 37

LEFT

Question 38

the more positive the E°, the further the eq lies to the …

Answer 38

RIGHT

Question 39

why must chemicals in a cell be kept separate

Answer 39

otherwise electron flow would be uncontrolled and heat energy would be produced instead of electrical

Question 40

standard electrode potential

Answer 40

emf of half cell when connected to a standard hydrogen half-cell under standard conditions

Question 41

limitations of predictions using Eθ values

Answer 41

• no indication of rate
• measured using 1 mol/dm3 conc - if conc higher then standard the value will be different
• actual conditions will be different from standard conditions
• standard electrodes apply to AQUEOUS equilibria - many reactions aren’t aqueous

Question 42

3 types of cell

Answer 42

• primary
• secondary
• fuel