Electrochemistry Flashcards
Define electrolysis.
breakdown of an ionic compound, when molten or in aqueous solution, by the passage of an electric current
What is the anode?
the positive electrode
What is the cathode?
the negative electron
What is the electrolyte?
the molten or aqueous substance that undergoes electrolysis
What process occurs at the anode?
oxidation
What process occurs at the cathode?
reduction
Why are metal objects electroplated?
to improve their appearance and resistance to corrosion
What process makes metal objects more resistant to corrosion and with improved appearance?
electroplating
What does a hydrogen–oxygen fuel cell do?
uses hydrogen and oxygen to produce electricity with water as the only chemical product
Electrolysis of MOLTEN LEAD(II) BROMIDE: product at the anode
bromine
Electrolysis of MOLTEN LEAD(II) BROMIDE: product at the cathode
lead
Electrolysis of MOLTEN LEAD(II) BROMIDE: observations
cathode: silvery solid
anode: brown gas
Electrolysis of concentrated aqueous NaCl: product at the anode
chlorine
Electrolysis of concentrated aqueous NaCl: product at the cathode
hydrogen
Electrolysis of concentrated aqueous NaCl: observations
cathode: colourless gas, lit splint squeaky pop
anode: pale yellow-green gas (turns UI red and bleaches red litmus)
Electrolysis of dilute sulfuric acid: product at the anode
oxygen
Electrolysis of dilute sulfuric acid: product at the cathode
hydrogen
Electrolysis of dilute sulfuric acid: observations
anode: colourless gas, relights glowing splint
cathode: colourless gas, lit splint squeaky pop
What forms at the cathode in the electrolysis of aqueous electrolytes?
cation below hydrogen in reactivity series- metal forms
cation above hydrogen- hydrogen gas forms, metal ion stays in solution
What forms at the anode in the electrolysis of aqueous electrolytes?
- halide ions (like Cl– , Br– or I–) present - the element will form (chlorine etc)
- other anions (eg sulfate, nitrate) - oxygen will form
- from the dissociation of OH– ions as nitrate/sulfate ions are more reactive than OH- ions
What forms at the anode in the electrolysis of molten electrolytes?
non-metal
What forms at the cathode in the electrolysis of molten electrolytes?
metal
What forms in the anode?
non-metals (other than hydrogen)
What forms in the cathode?
metals, or hydrogen
Advantages of hydrogen fuel cell
high energy density, high fuel efficiency, minimal pollution
Disadvantages of hydrogen fuel cells
hydrogen has to be produced (often involving burning fossil fuels), stored as a compressed gas so difficult to transport, highly flammable
a hydrogen–oxygen fuel cell uses
hydrogen and oxygen to produce electricity with water as the only chemical product
Describe how metals are electroplated.
metal ions migrate via a solution from a positive electrode to a negative one
why are metal objects electroplated
improve their appearance and resistance to corrosion.
Describe the extraction of aluminium from purified bauxite / aluminium oxide
- Bauxite is first purified to produce aluminium oxide, Al2O3
- Aluminium oxide is then dissolved in molten cryolite
- This is because aluminium oxide has a melting point of over 2000°C which would use a lot of energy and be very expensive
- The resulting mixture has a lower melting point without interfering with the reaction
- The mixture is placed in an electrolysis cell, made from steel, lined with graphite
- The graphite lining acts as the negative electrode, with several large graphite blocks as the positive electrodes
aluminium cathode
Al3+ + 3e- → Al
aluminium anode
2O2- → O2 + 4e-
aluminium overall
2Al2O3 → 4Al + 3O2
Explain why the carbon anode has to be replaced regularly.
carbon reacts with oxygen and forms carbon dioxide
aqueous copper (II) sulphate products in graphite
cathode: copper
anode: oxygen
aqueous copper (II) sulphate products in copper
cathode: copper
anode: copper
reduction of hydrogen
2H+(aq) + 2e– → H2(g)
hydroxide equation
4OH–(aq)→2H2O(l)+O2(g)+4e–
