C4 electrochemistry

Question 2

define electrolysis

Answer 2

• decomposition of an ionic compound (whether molten or aqueous solution)
• by passage of electric current

Question 3

what is the anode

Answer 3

positive electrode

Question 4

what is the cathode

Answer 4

negative electrode

Question 5

what is an electrolyte

Answer 5

the molten/aqueous substance that undergoes electrolysis

Question 6

product formed at cathode during electrolysis of lead bromide

Answer 6

lead (silvery solid)

Question 7

product formed at anode during electrolysis of molten lead bromide

Answer 7

bromine (bubbles of brown gas)

Question 8

product formed at cathode during electrolysis of aqueous sodium chloride

Answer 8

hydrogen (bubbles of colourless gas)

Question 9

product formed at anode during electrolysis of aqueous sodium chloride

Answer 9

chlorine (bubbles of pale yellow-green gas)

Question 10

product formed at cathode during electrolysis of dilute sulfuric acid

Answer 10

hydrogen (bubbles of colourless gas)

Question 11

product formed at anode during electrolysis of sulfuric acid

Answer 11

oxygen (bubbles of colourless gas)

Question 12

what happens to electrons in external circuit during electrolysis

Answer 12

• travel thru external circuit
• lost/gained at electrodes

Question 13

movement of ions in electrolyte during electrolysis

Answer 13

• cations attracted to cathode
• anions attracted to anode

Question 14

what occurs at cathode during electrolysis

Answer 14

• cations attracted
• gain electrons
• become atoms

Question 15

what happens at anode during electrolysis

Answer 15

• anions attracted
• lose electrons
• become atoms

Question 16

what element is formed at cathode

Answer 16

METALS OR HYDROGEN
- if product more reactive than hydrogen, hydrogen formed
- else, product formed

Question 17

what element is formed at anode

Answer 17

NON-METALS (OTHER THAN HYDROGEN
- if halide present, halide formed
- else, oxygen

Question 18

observations at cathode during electrolysis of aqueous copper (II) sulfate using carbon (graphite) electrodes

Answer 18

orange-brown copper forms on cathode

Question 19

observations at anode during electrolysis of aqueous copper (II) sulfate using carbon (graphite) electrodes

Answer 19

bubbles of oxygen are given off

Question 20

observations at cathode during electrolysis of aqueous copper (II) sulphate using copper electrodes

Answer 20

orange-brown copper forms on cathode

Question 21

observations at anode during electrolysis of aqueous copper (II) sulfate using copper electrodes

Answer 21

• anode loses mass as copper ions leave it
• sludge forms under anode (impurities in copper)

Question 22

state the reaction in a hydrogen-oxygen fuel cell

Answer 22

2H2o (g) + O2 (g) –> 2H2O (g)

Question 23

is the reaction in a hydgrogen-oxygen fuel cell endo or exo

Answer 23

exothermic

Question 24

what is a hydrogen-oxygen fuel cell

Answer 24

• produce energy
• using hydrogen and oxygen
• water is only chemical product

Question 25

advantages of using hydrogen-oxygen fuel cells over gasoline / petrol engines

Answer 25

• highly efficient
• renewable
• plentiful cheap supply of reactants
• zero carbon emissions

Question 26

disadvantages of using hydrogen-oxygen fuel cells over gasoline / petrol engines

Answer 26

• lack of facilities/methods for widespread use
• reactants are gases so must be compressed for storage (hazardous)
• sourcing hydrogen may be expensive/non renewable