electrochemistry

Question 1

define electrolyte

Answer 1

an aqueous or ionic compound that is conducting electricity

Question 2

what metal out of copper or magnesium is more reactive

Answer 2

magnesium as it loses electrons more

Question 3

which species is more likely to be reduced

Pb4+ + 2e- ⇌ Pb2+
Electrode potential = 1.67 v

2H+ + 2e- ⇌ H2
Electrode potential = 0.00 v

Answer 3

Pb4+ as the electrode potential is the most positive so most likely to gain electrons

Question 4

which species is more likely to be oxidised

Cl2 + 2e- ⇌ 2Cl-
Electrode potential = 1.67 v

Mg2+ + 2e- ⇌ Mg
Electrode potential = -2.36 v

Answer 4

Mg as the electrode potential is most negative so most likely to lose electrons

Question 5

explain the procedure for standard cell representation

Answer 5

• reverse direction of the half equation with most negative electrode potential
• most negative half equation goes on left, most positive goes on the right
• double line indicates a salt bridge ||
• electrodes go on the outside
• phase changes are shown by a single line |
• species in the same phase are separated by a comma (,)

Question 6

how do you calculate cell emf

Answer 6

cell emf = right electrode potential - left electrode potential

Question 7

how do electrons flow in an electrochemical cell

Answer 7

electrons flow from the most negative electrode to the most positive electrode

(tends to be from left to right)

Question 8

do electrons flow when there is a voltmeter in the circuit

Answer 8

electrons do not flow when a voltmeter is used in the circuit

Question 9

what happens to emf over time and why

Answer 9

emf decreases as the reactants get used up

and the cell discharges

Question 10

what factors affect the cell emf of an electrochemical cel

Answer 10

concentration

temperature

Question 11

where does the hydrogen reference electrode always go

Answer 11

on the left

Question 12

what is the emf of the circuit with the hydrogen reference electrode equal to

Answer 12

the emf of the circuit with the hydrogen reference electrode equal to the electrode potential of the half cell it is connected to

Question 13

what are the 3 standard conditions associated with the hydrogen reference electrode

Answer 13

H2 gas at 100 kPa

1.00 mol dm-3 HCl

298 K

Question 14

what happens if the change pushes the equilibrium towards X in terms of electrode potential

X+ + e- → X

Answer 14

if changes pushes equilibrium towards X then electrode potential becomes more positive

Question 15

what happens if the change pushes the equilibrium towards X+ in terms of electrode potential

X+ + e- → X

Answer 15

if change pushes equilibrium towards X+ then electrode potential becomes less positive (more negative)

Question 16

what are the 4 steps to combining half equations

Answer 16

1. reverse direction of equation with most negative electrode potential
2. multiply equations so that the number of electron balance
3. combine all reactants and all products
4. cancel out all species that are the same on both sides

Question 17

define electrochemical series

Answer 17

a list of half equations in order of electrode potential

Question 18

what is the strongest reducing agent in the electrochemical series

Answer 18

the species on the right with the most negative electrode potential (as it is most likely to be oxdised)

Question 19

what is the strongest oxidising agent in the electrochemical series

Answer 19

the species on the left with the most positive electrode potential (most likely to be reduced0

Question 20

What are species with a more negative electrode potential likely to do

Answer 20

species with a more negative electrode potential are able to reduce those with a more positive electrode potential

Question 21

what are species with a more positive electrode potential likely to do

Answer 21

species with a more positive electrode potential are able to oxidise those with a more negative electrode potential

Question 22

write the equations for the positive and negative electrode in a lithium ion cell

Answer 22

positive electrode

Li+ + CoO2 + e- → Li+CoO2 - +1.01 v

negative electrode

Li → Li+ + e-

Question 23

write an equation for the discharge of lithium electrochemical cell in an iron casing

Answer 23

Li+ + CoO2 → Li+CoO2 -