Electrochemistry Flashcards
What is the anode?
Positive electrode, oxidation reaction
What is the cathode?
Negative electrode, reduction reaction
Why do electrodes need to be inert?
need to be inert such as graphite or platinum so that they don’t participate in a side reaction with the electrolyte
What is the electrolyte?
The molten or aqueous
substance that undergoes electrolysis
Why are metals electroplated?
Metal objects are electroplated to improve their appearance and resistance to corrosion
Ionic half equation when hydrogen forms at the cathode
2H+ + 2e- → H2
Ionic half equation when oxygen forms at the cathode
4(OH)- → 2H2O + O2 + 4e-
Process of electroplating
Theanodeis made from thepuremetal you want to coat your object with. Thecathodeis theobjectto be electroplated. The electrolyte is an aqueous solution of an ionic compound of the plating metal. The atoms in the electrode on the anode lose electrons and become ions. These are sent over to the cathode where they are turned back into atoms and plate the cathode
What happens in the electrolysis of aqueous copper(II) sulfate using copper electrodes
- Thecathode increasesin mass while theanodedecreases. This occurs as copper atoms areoxidisedat the anode and form ions while copper ions arereducedat the cathode, forming copper atoms. The gain in mass by the negative electrode is thesameas the loss in mass by the positive electrode. Therefore, the copper deposited on the negative electrode must be thesamecopper ions that are lost from the positive electrode
- The copper atoms in the electrode on the anode lose electrons and become copper ions. These are sent over to the cathode where they are turned back into copper atoms. Therefore, the anode loses weight and the cathode gains weight.
Transfer of charge in electrolysis
- During electrolysis, current needs to flow around the circuit. In order for this to occur, charge must be transferred around the circuit (current is a measure of the rate of flow of charge) by charge carriers.
- The power supply provides thecathodewith a supply ofelectrons, causing it to become negatively charged.
- Positive ions(cations) in the electrolyte move towards the cathode where theygain electrons to become atoms (in a positive ion, there are more protons than electrons, so in order to become an atom, they need to gain those extra electrons to become neutral). Soreduction occurs at the cathode.
- Negative ions(anions) in the electrolyte move towards the anode where theylose electrons to become atoms (in a negative ion, there are more electrons than protons, so in order to become an atom, they need to lose those extra electrons to become neutral). Sooxidation occurs at the anode.
- Theelectronsmove from the anode back towards the power supply which then goes back to the cathode creating a circuit.
Hydrogen fuel cell what does it use and what’s the byproduct?
a hydrogen–oxygen fuel cell uses hydrogen and oxygen to produce electricity with water as the only chemical product
Advantages of hydrogen fuel cells
- Theydo not produceanypollution: the only product is water whereas petrol engines producecarbon dioxide,and oxides of nitrogen
- They releasemoreenergyper kilogram than either petrol or diesel
- No power is lost in transmission as there are no moving parts, unlike an internal combustion engine
- Quieter so less noise pollution compared to a petrol engine
Disadvantages of hydrogen fuel cells
- Materials used in producing fuel cellsareexpensive
- Hydrogen is more difficult and expensive to store compared to petrol as it is very flammable and easily explodes when under pressure
- Fuel cells are affected bylowtemperatures, becoming less efficient
- There are only a small number of hydrogen filling stations across the country
- Hydrogen is often obtained by methods that involve the combustion of fossil fuels, therefore releasing carbon dioxide and other pollutants into the atmosphere
