electrolytic processes

Question 1

what are electrolytes

Answer 1

ionic compounds in the molten state or dissolved in water

Question 2

describe electrolysis

Answer 2

• electric current is passed through electrolyte
• causing it to decomposes

Question 3

explain the movement of ions during electrolysis:

Answer 3

a) positvely charged cations migrate to negatively charged cathode
b) negatively charged anions migrate to positively charged anode

Question 4

where do cations migrate to

Answer 4

the negatively charged cathode

Question 5

where do anions migrate to

Answer 5

the positively charged anode

Question 6

what happens when cations in the electyrolyte move towards the cathode (negative electrode)

Answer 6

• cations move towards cathode
• and are reduced (gain electrons)

Question 7

what happens when anions in the electrolyte move towards the anode (positive electrode)

Answer 7

• anions move towards anode
• and are oxidised (lose electrons)

Question 8

Explain the formation of the products in the electrolysis, using inert electrodes, of some electrolytes, including:
a) copper chloride solution

Answer 8

• copper ions go to cathode
• copper is produced
• (copper is less reactive than hydrogen)
• chlorine ions go to anode
• chlorine gas is produced
• (clhorine are halide ions)

Question 9

Explain the formation of the products in the electrolysis, using
inert electrodes, of some electrolytes, including:
b) sodium chloride solution

Answer 9

• hydrogen ions go to cathode
• hydrogen gas is produec
• (sodium is more reactive than hydrogen)
• chlorine ions go to anode
• chlorine gas is poruduced
• (chlorine are halide ions)

Question 10

Explain the formation of the products in the electrolysis, using
inert electrodes, of some electrolytes, including:
c) sodium sulfate solution

Answer 10

• hydrogen ions go to cathode
• hydrogen gas in produced
• sodium is more reactive than hydrogen
• hydroxide ions to to anode
• oxygen gas is produced
• sulphate ions are not halide ions

Question 11

Explain the formation of the products in the electrolysis, using
inert electrodes, of some electrolytes, including:
d) water acidified with sulfuric acid

Answer 11

• hydrgoen to cathode
• hydrogen gas produced
• (these are the other ions present in sulfuric acid H2SO4)
• hydroxide ions to anode
• oxygen gas is produced
• (SO42- ions are not halide ions)

Question 12

Explain the formation of the products in the electrolysis, using
inert electrodes, of some electrolytes, including:
e) molten lead bromide

Answer 12

• lead to cathode
• lea dis proudecd
• (not in solution so these are the only + ions present)
• bromine to anode
• bromine liquid is proudced
• (not is solution so these are the only - ions present)

Question 13

what woll your solution contain when you have an ionic solution (NOT molten ionis compound) ((products of electrolysis usining inert electrodse))

Answer 13

• the ions that mak eup the ionic compound
• the ions in water (OH- and H+)

Question 14

what happens at the cathode (products of electrolysis) (using inert electrodes)

Answer 14

• hydeogen (from H+ in water) is proudec
• unless the + ions in the ionic compoun are from a metal less reactive than hydrogen
• if teh metal is less reactive (than hydrogen) it will be proudced instead

Question 15

what happens at the anode (products of electrolysis) (using inert electrodes)

Answer 15

• ocygen (from OH- in water) will be proudced
• unless the ionic compound contains halide ions (cl, br , i (minuses) )
• if there are halide ions the halogen will be produced instead

Question 16

predict the products of electrolysis of other binary, ionic compounds in the molten state

Answer 16

-identify which ions there are within the ionic compound
- the + ions will go to cathode
- the - ions will go to anode

Question 17

why is it easier to predict the products of electrolysis in the molten state

Answer 17

no ions present except those in the ionic compound

Question 18

what do half equations show

Answer 18

how electrons are transferred during reactions
- what happens at each electrode during electrolysis

Question 19

how to write half reactions in electrolysis

Answer 19

1. put one of the things being oxidised or reduced on one side of arrow
2. the thing it gets oxidised or reduced to on the other
3. balance the numbers of atoms
4. add electrons (e-) on to one side to balance up charges

Question 20

example of electrolysis half equation

Answer 20

Na -> Na+ + e - (sodium losing one electron to become a sodium ion

2H+ + 2e- -> H2 (hydrogen ions are gaining electrons to become hydrogen)

Question 21

what a half equation looks like for the reactions at each electrode a) negative electrode

Answer 21

X+ -> X , so ionic equation must be,

X+ + e- -> X (electons gained so positive ions are reduced)

(OILRIG)

Question 22

what a half equation looks like for the reactions at each electrode
b) positive electrode

Answer 22

X -> X , so ionic equation must be,

X -> e - + X 9electrons are lost so negative ions are oxidised)

(OILRIG)

Question 23

explain oxidation and reduction in terms of loss or gain of electrons

Answer 23

• oxidation is LOSS (of electrons)
• reduction is GAIN (of electrons)

(OILRIG)

Question 24

reduction occurs at the

Answer 24

cathode

Question 25

oxidation occurs at the

Answer 25

anode

Question 26

anode means

Answer 26

- loss of electrons - oxidation of anions (-) - would have to lose electrons to have a neutral charge

Question 27

cathode means

Answer 27

- gain of electrons - reduction of cations (+) - would have to gain electrons to get a neutral charge

Question 28

explain the formation of the products in the electrolysis of copper sulfate solution, using copper electrodes a) what is needed to set up

Answer 28

1. anode is made of impure copper (that you're purifying) 2. cathode is made of pure copper 3. solution is copper sulfate

Question 29

explain the formation of the products in the electrolysis of copper sulfate solution, using copper electrodes b) what happens

Answer 29

1. copper ions from the anode move to the cathode - where they fain electrons and are dishcagred as pure copper 2. impurities form as sludge below the anode

Question 30

explain the formation of the products in the electrolysis of copper sulfate solution, using copper electrodes c) how this electrolysis can be used to purify copper

Answer 30

- the cathode will increase in mass as it gains pure copper - anode will lose mass as copper ions are lost (they replace the ones from teh CuSO4 solution that go to the cathode) - and so are impurities

Question 31

core practical: investigate the electrolysis of copper sulfae solution with inert electrodes

Answer 31

- at the cathode copper is produced (copper less reactive than hydrogen) - at the anode oxygen is produced (SO42- ions are not halide ions) - this leaves H+ and SO42- ions in the solution which will react to form H2SO4- sulfuric acid

Question 32

core practical, investiage the electrolysis of copper sulfate solution with copper electrodes

Answer 32

- copper ions deposited as copper at the cathode from the solution are replaced with - copper ions from the anode - so concentration of copper ions in the solution remains constant