C9 Electrolysis and Energy Flashcards
what is electrolysis?
breaking down ionic compounds by the passage of electricity
electrolysis can only take place under what conditions? why?
in solution or molten
cuz electrons must be free to move
what is ELECTROLYTE?
substance being broken down
what must an electrolyte be able to do? how do you test it?
must conduct electricity
test: ammeter
what materials is the ELECTRODE usually made of? why?
graphite/platinum
cuz they are INERT
is CATHODE (+) or (-) ?
(-)
is ANODE (+) or (-) ?
(+)
ELECTROLYSIS:
what happens as electric current passes through the cell? (explain in terms of electrodes and ions)
CATIONS+ attracted to CATHODE-
→ gain electrons → form atoms
ANIONS- attracted to ANODE+
→ lose electrons → form atoms
MOLTEN:
what is produced at the CATHODE?
metal
MOLTEN:
what is produced at the ANODE?
non-metal
IN SOLUTION:
what is produced at the CATHODE if the ion is MORE reactive than H? why?
hydrogen gas
cuz more reactive ions prefer to stay as ions
IN SOLUTION:
what is produced at the CATHODE if the ion is LESS reactive than H?
metal
IN SOLUTION:
what is produced at the ANODE if the ions are HALOGEN?
halogen gas
IN SOLUTION:
what is produced at the ANODE if the ions are NOT HALOGEN?
oxygen gas
IN SOLUTION:
what happens if the halide solution is VERY DILUTE? why?
OXYGEN gas will be given off instead of the halogen gas
cuz the halogen ions are outnumbered by the OH ions in water.
how do you PURIFY COPPER?
what do you put at the cathode and the anode? (pure/impure copper)
pass electricity through solutions containing copper compounds
- cathode: pure copper
- anode: impure copper
PURIFY COPPER:
what happens as electric current passes through? (3)
- ANODE: Cu atoms lose electrons → enter solution as Cu+ ions
- CATHODE: Cu+ ions are attracted → gain electrons and form atoms → pure copper
- impurities at anode drop to bottom as SLIME
coating one metal with another by the pass of electricity is called?
electroplating
ELECTROPLATING:
what do you put at the cathode and the anode?
cathode: object to be coated
anode: what coats the object
formula of LIMESTONE
CaCO3
formula of LIME
CaO
formula of LIMEWATER (slaked lime)
Ca(OH)2
how do you THERMALLY DECOMPOSE LIMESTONE? what is the EQUATION and what OBSERVATION shows this reaction is happening?
heat:
CaCO3 → CaO + CO2
limestone becomes white
how do you turn LIME → LIMEWATER (slaked lime)? what is the EQUATION and what OBSERVATION shows this reaction is happening?
add water:
CaO + H2O → Ca(OH)2
exothermic, water hisses
how do you turn LIMEWATER → LIMESTONE? what is the EQUATION and what OBSERVATION shows this reaction is happening?
blow CO2 bubbles:
Ca(OH)2 + CO2 → CaCO3 + H2O
limewater turns cloudy
uses of limestone
neutralize acidic soil and industrial waste
is limestone acidic or basic? what can be used to show this?
basic universal indicator (green → blue)
what happens during EXOTHERMIC reaction?
explain in terms of heat, energy and bonds
energy released in forming bonds in products > energy absorbed in breaking bonds in reactants → heat energy is LOST/RELEASED to surrounding
what happens during ENDOTHERMIC reaction?
explain in terms of heat, energy and bonds
energy released in forming bonds in products < energy absorbed in breaking bonds in reactants → reactants GAIN/ABSORB HEAT heat energy from surrounding
example of EXOTHERMIC reaction
combustion, oxidation, neutralization
example of ENDOTHERMIC reaction
thermal decomposition, melting ice, boiling water
draw diagrams to show energy change in exothermic and endothermic reactions
check notes :)
