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IGCSE Chemistry > C9 Electrolysis and Energy > Flashcards

C9 Electrolysis and Energy Flashcards

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1
Q

what is electrolysis?

A

breaking down ionic compounds by the passage of electricity

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2
Q

electrolysis can only take place under what conditions? why?

A

in solution or molten

cuz electrons must be free to move

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3
Q

what is ELECTROLYTE?

A

substance being broken down

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4
Q

what must an electrolyte be able to do? how do you test it?

A

must conduct electricity

test: ammeter

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5
Q

what materials is the ELECTRODE usually made of? why?

A

graphite/platinum

cuz they are INERT

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6
Q

is CATHODE (+) or (-) ?

A

(-)

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7
Q

is ANODE (+) or (-) ?

A

(+)

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8
Q

ELECTROLYSIS:

what happens as electric current passes through the cell? (explain in terms of electrodes and ions)

A

CATIONS+ attracted to CATHODE-
→ gain electrons → form atoms

ANIONS- attracted to ANODE+
→ lose electrons → form atoms

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9
Q

MOLTEN:

what is produced at the CATHODE?

A

metal

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10
Q

MOLTEN:

what is produced at the ANODE?

A

non-metal

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11
Q

IN SOLUTION:

what is produced at the CATHODE if the ion is MORE reactive than H? why?

A

hydrogen gas

cuz more reactive ions prefer to stay as ions

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12
Q

IN SOLUTION:

what is produced at the CATHODE if the ion is LESS reactive than H?

A

metal

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13
Q

IN SOLUTION:

what is produced at the ANODE if the ions are HALOGEN?

A

halogen gas

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14
Q

IN SOLUTION:

what is produced at the ANODE if the ions are NOT HALOGEN?

A

oxygen gas

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15
Q

IN SOLUTION:

what happens if the halide solution is VERY DILUTE? why?

A

OXYGEN gas will be given off instead of the halogen gas

cuz the halogen ions are outnumbered by the OH ions in water.

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16
Q

how do you PURIFY COPPER?

what do you put at the cathode and the anode? (pure/impure copper)

A

pass electricity through solutions containing copper compounds

  • cathode: pure copper
  • anode: impure copper
17
Q

PURIFY COPPER:

what happens as electric current passes through? (3)

A
  1. ANODE: Cu atoms lose electrons → enter solution as Cu+ ions
  2. CATHODE: Cu+ ions are attracted → gain electrons and form atoms → pure copper
  3. impurities at anode drop to bottom as SLIME
18
Q

coating one metal with another by the pass of electricity is called?

A

electroplating

19
Q

ELECTROPLATING:

what do you put at the cathode and the anode?

A

cathode: object to be coated
anode: what coats the object

20
Q

formula of LIMESTONE

A

CaCO3

21
Q

formula of LIME

A

CaO

22
Q

formula of LIMEWATER (slaked lime)

A

Ca(OH)2

23
Q

how do you THERMALLY DECOMPOSE LIMESTONE? what is the EQUATION and what OBSERVATION shows this reaction is happening?

A

heat:
CaCO3 → CaO + CO2

limestone becomes white

24
Q

how do you turn LIME → LIMEWATER (slaked lime)? what is the EQUATION and what OBSERVATION shows this reaction is happening?

A

add water:
CaO + H2O → Ca(OH)2

exothermic, water hisses

25
Q

how do you turn LIMEWATER → LIMESTONE? what is the EQUATION and what OBSERVATION shows this reaction is happening?

A

blow CO2 bubbles:
Ca(OH)2 + CO2 → CaCO3 + H2O

limewater turns cloudy

26
Q

uses of limestone

A

neutralize acidic soil and industrial waste

27
Q

is limestone acidic or basic? what can be used to show this?

A 
basic
universal indicator (green → blue)
28
Q

what happens during EXOTHERMIC reaction?

explain in terms of heat, energy and bonds

A

energy released in forming bonds in products > energy absorbed in breaking bonds in reactants → heat energy is LOST/RELEASED to surrounding

29
Q

what happens during ENDOTHERMIC reaction?

explain in terms of heat, energy and bonds

A

energy released in forming bonds in products < energy absorbed in breaking bonds in reactants → reactants GAIN/ABSORB HEAT heat energy from surrounding

30
Q

example of EXOTHERMIC reaction

A

combustion, oxidation, neutralization

31
Q

example of ENDOTHERMIC reaction

A

thermal decomposition, melting ice, boiling water

32
Q

draw diagrams to show energy change in exothermic and endothermic reactions

A

check notes :)

IGCSE Chemistry (9 decks)

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