Electrochemistry * Flashcards
What is electrochemistry?
the process by which ionic substances are broken down into simpler substances when an electric current is passed through them
or
using electrical energy to break ionic bonds
What is the electrolyte?
the ionic substance that is broken down
What may form at the electrodes during electrolysis?
metals and gases
What are cations?
positively charged ions (remember paw-sitive)
What are anions?
negatively charged ions
Where do the cations go during electrolisys?
to the cathode
Where do anions go during electrolysis?
to the anode
What charge does the cathode have?
negative
What charge does the anode have?
positive
Give the formula and charge of these cations:
silver
copper (II)
hydrogen
lead (II)
magnesium
aluminium
sodium
Ag+
Cu 2+
H+
Pb 2+
Mg 2+
Al 3+
Na+
Give the formulae and charge of these anions:
sulfate
nitrate
hydroxide
chloride
bromide
iodide
SO4 2-
NO3 -
OH-
Cl-
Br-
I-
Fill the gaps:
- metal ions are all _______
- non-metals are all ______
- the only exception is ________ which is positive (______)
- metal ions are all cations
- non-metals are all anions
- the only exception is hydrogen which is positive (cation)
Do cations gain or lose electrons at the cathode?
cations gain electrons
Do anions gain or lose electrons at the anode?
anions lose electrons
What is formed at the cathode? (aqueous electrolytes)
Whatever is lowest in the reactivity series
What is formed at the anode? (aqueous electrolytes)
oxygen and water unless something from group 7 is present (Cl-, Br-, I-)
What is the half equation? (aqueous electrolytes)
4OH- –> 2H2O + O2 + 4e-
What is electroplating?
when electrolysis is used to form a layer of metal over the surface of another metal
Why is electroplating used?
to make objects made from a cheap material look more attractive (e.g. coat with silver or gold)
protect metals that corrode easily with a layer of a less reactive material
What else is electrolysis used for? (2 points)
- extraction of reactive materials
- producing hydrogen from water
What are electrochemical cells?
they consist of two half-cells connected together by an external circuit and a salt bridge
(electrochemical cells)
What type of reactions occur in the half-cells and what kind of energy is produced?
exothermic reaction
electrical energy is produced instead of heat - this is the voltage/potential difference
(electrochemical cells)
What happens when one of the reactants in the half cell is used up?
the reactions stop and a voltage is no longer produced
What are fuel cells?
combustion reactions that produce electrical energy instead of heat
What is an example of a fuel cell?
the hydrogen-oxygen fuel cell
What happens at the anode in a hydrogen fuel cell?
hydrogen molecules break up into atoms which lose their electrons and form hydrogen ions
What happens at the cathode in a hydrogen fuel cell?
the hydrogen ions gain electrons and then react with oxygen
What is the overall reaction in a hydrogen fuel cell?
2H2 + O2 –> 2H2O
What are 4 pros and cons of hydrogen fuel cells?
pros:
- unlimited supply of hydrogen (made from water)
- doesn’t produce greenhouse gases
- renewable resource
- very powerful
cons:
- hard to store
- requires a lot of energy to make
- expensive
- time-consuming
What is a non-electrolyte?
doesn’t conduct electricity
What happens during reduction?
an ion gains electrons and becomes an atom
What happens during oxidation?
an atom loses electrons and becomes an ion
