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combined chemistry > electrolytic processes > Flashcards

electrolytic processes Flashcards

topic 3 - chemical change

1
Q

what are electrolytes

A

ionic compounds in the molten state or dissolved in water

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2
Q

describe electrolysis

A
  • electric current is passed through electrolyte
  • causing it to decomposes
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3
Q

explain the movement of ions during electrolysis:

A

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

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4
Q

where do cations migrate to

A

the negatively charged cathode

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5
Q

where do anions migrate to

A

the positively charged anode

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6
Q

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

A
  • cations move towards cathode
  • and are reduced (gain electrons)
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7
Q

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

A
  • anions move towards anode
  • and are oxidised (lose electrons)
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8
Q

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

A
  • 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)
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9
Q

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

A
  • 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)
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10
Q

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

A
  • 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
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11
Q

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

A
  • 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)
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12
Q

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

A
  • 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)
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13
Q

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

A
  • the ions that mak eup the ionic compound
  • the ions in water (OH- and H+)
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14
Q

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

A
  • 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
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15
Q

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

A
  • 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
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16
Q

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

A

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

17
Q

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

A

no ions present except those in the ionic compound

18
Q

what do half equations show

A

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

19
Q

how to write half reactions in electrolysis

A
  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
20
Q

example of electrolysis half equation

A

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

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

21
Q

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

A

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

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

(OILRIG)

22
Q

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

A

X -> X , so ionic equation must be,

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

(OILRIG)

23
Q

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

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

(OILRIG)

24
Q

reduction occurs at the

A

cathode

25
Q

oxidation occurs at the

A

anode

26
Q

anode means

A
  • loss of electrons
  • oxidation of anions (-)
  • would have to lose electrons to have a neutral charge
27
Q

cathode means

A
  • gain of electrons
  • reduction of cations (+)
  • would have to gain electrons to get a neutral charge
28
Q

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

A
  1. anode is made of impure copper (that you’re purifying)
  2. cathode is made of pure copper
  3. solution is copper sulfate
29
Q

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

A
  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
30
Q

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

A
  • 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
31
Q

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

A
  • 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
32
Q

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

A
  • 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

combined chemistry (11 decks)

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