Redox

Question 1

what 3 things can you add to ionic half equations ?

Answer 1

H+ / e- / H2O

Question 2

what is the colour change w/ MnO4- titration ?

Answer 2

purple to colourless

Question 3

what is the colour change w/ dichromate titration ?

Answer 3

orange to green

Question 4

outline the process of a redox titration

Answer 4

• measure quantity of unknown conc sol. using pipette into conical flask
• add dilute acid
• gradually add known conc sol. using burette
• stop when mixture changes colour and record vol of oxidising agent used
• repeat and calculate mean titre

Question 5

what is Iodine-thiosulfate titration used for ?

Answer 5

finding concentration of an oxidising agent

Question 6

outline the process of finding oxidising agent conc Iodine-thiosulfate titration

Answer 6

1. add set vol of [O] agent to excess of KI to form Iodine
2. Iodine-thiosulfate titration
3. calculate no. of moles of iodine in solution
4. calculate conc of [O] w/ first equation

Question 7

outline the process of Iodine-thiosulfate titration

Answer 7

1. add sodium thiosulfate to iodine using burette
2. when Iodine solution fades to pale yellow, add starch solution, turning solution blue
3. continue to add sodium thio. slowly until decolourises

Question 8

what is the salt bridge ?

Answer 8

filter paper soaked in potassium nitrate, which allows ions to flow through and balance charges

Question 9

what electrode is used when no solid metal for electrochemical cell ?

Answer 9

platinum

inert and conducts electricity

Question 10

in an electrochemical cell, electrons flow ..

Answer 10

from most reactive metal to least

Question 11

more negative electrode potential means ..?

Answer 11

more easily oxidised - loses electrons

Question 12

electrode potential of cell =

Answer 12

electrode potential of positive - electrode potential of negative

Question 13

define standard electrode potential

Answer 13

voltage measured when the half-cell is connected to a standard hydrogen electrode, under standard conditions

Question 14

a more reactive metal will have a … electrode potential

Answer 14

more negative

Question 15

a more reactive NON metal will have a … electrode potential

Answer 15

more positive

Question 16

what equation is at the anode of a fuel cell ?

Answer 16

H2 –> 2H+ + 2e-

Question 17

what equation is at the cathode of a fuel cell ?

Answer 17

1/2 O2 + 2H+ +2e- –> H2O

Question 18

what goes in / out at the anode of fuel cell ?

Answer 18

fuel (H2) in / unused fuel out

Question 19

what goes in / out at the cathode of fuel cell ?

Answer 19

oxidant (O2) in / water out

Question 20

which direction do electrons flow in fuel cell ?

Answer 20

2 electrons from anode to cathode

Question 21

state the advantages of electrochemical cells

Answer 21

• more efficient than conventional combustion engines

- produce less pollution

Question 22

state the disadvantages of electrochemical cells

Answer 22

• toxic chemicals in cell must be disposed of at end of cell life
• chemicals used to make cells are often very flammable

Question 23

state one difference between fuel cell and modern storage cell

Answer 23

fuel like oxygen required to give electrical voltage

Question 24

state an advantage of using ethanol over hydrogen as a fuel

Answer 24

is a liquid (less volatile) so easier to store

Question 25

state an advantage of using hydrogen over conventional fuels

Answer 25

water is only product (no carbon dioxide)

Question 26

state ways hydrogen can be stored as a fuel

Answer 26

• liquid under pressure

- within solid material

Question 27

suggest two reasons for feasible electrode potential reactions not taking place ?

Answer 27

• Ea very high

- conditions not standard