Electrochemistry Flashcards
Electrolysis Definition
Electrolysis is the decomposition of an ionic compound, when molten or in aqueous solution, by the passage of an electric current
Identify in simple electrolytic cells :
- the anode
- the cathode
- the electrolyte
- the anode as the positive electrode
- the cathode as the negative electrode
- the electrolyte as the molten or aqueous substance that undergoes electrolysis
Describe the transfer of charge during electrolysis
(a) the movement of electrons in the external circuit
(b) the loss or gain of electrons at the electrodes
(c) the movement of ions in the electrolyte
(a) During electrolysis, electrons flow through the external circuit from the negative electrode (cathode) to the positive electrode (anode). This movement of electrons constitutes an electric current.
(b) An Ox Red Cat - Anode Oxidation of Anions, Cathode Reduction of Cations
(c) Within the electrolyte, positively charged ions migrate towards the cathode, while negatively charged ions migrate towards the anode.
Identify products formed at the electrodes and describe the observations made during the electrolysis of:
(a) molten lead(II) bromide
(b) concentrated aqueous sodium chloride
(c) dilute sulfuric acid
using inert electrodes made of platinum or carbon/ graphite
electrolysis of aqueous copper(II) sulfate
(a) using inert carbon/ graphite electrodes
(b) when using copper electrodes
(a) Molten lead(II) bromide:
At the cathode: Lead metal is formed as lead ions gain electrons.
At the anode: Bromine gas is produced as bromide ions lose electrons.
Observations: The lead cathode will become coated with lead metal, while reddish-brown bromine gas will be observed at the anode.
(b) Concentrated aqueous sodium chloride (Brine solution):
At the cathode: Hydrogen gas is produced as sodium ions are more reactive than hydrogen.
At the anode: Chlorine gas is evolved as chloride ions lose electrons.
Observations: Hydrogen gas forms at the cathode, while a greenish-yellow gas (chlorine) will be observed at the anode.
(c) Dilute sulfuric acid:
At the cathode: Hydrogen gas is evolved as hydrogen ions gain electrons.
At the anode: Oxygen gas is produced as water molecules lose electrons.
Observations: Hydrogen gas bubbles will be observed at the cathode, while oxygen gas bubbles will be observed at the anode.
Electrolysis of aqueous copper(II) sulfate:
(a) Using inert carbon/graphite electrodes:
At the cathode: Copper metal is deposited as copper ions gain electrons.
At the anode: Oxygen gas is evolved as water molecules lose electrons.
Observations: A reddish-brown deposit of copper will form on the cathode, while oxygen gas bubbles will be observed at the anode.
(b) When using copper electrodes:
At the cathode: Copper metal is still deposited as copper ions gain electrons.
At the anode: Copper metal dissolves into copper ions as it loses electrons.
Observations: A layer of copper metal will form on the cathode, while the anode will gradually decrease in size as copper ions are released into the solution.
Generally, How would you find what is formed at the cathode and at the anode?
(a) Molten Electrolysis
(b) Aqueous Electrolysis
(a) Molten Electrolysis
- Cathode (-) : Metal
- Anode (+) : Non-Metal
(b) Aqueous Electrolysis
-Cathode (-) :
If Metal has lower reactivity than H₂, the Metal will form.
If Metal has higher reactivity than H₂, H₂ Gas will form.
-Anode (+) :
if a halide (halogen compound) is not present, O₂ gas will form.
if a halide is present, if it is aqueous, O₂ gas will form,
if it is concentrated, halogen gas forms
Constructing ionic half-equations for reactions at the anode (to show oxidation) and at the cathode (to show reduction)
At Cathode (-) : Reduction (gain of electrons)
Positive ion + 2e -> Element
At Anode (+) : Oxidation (loss of electrons)
Negative Ion -> Element + 2e
Why are metal objects are electroplated ?
Metal objects are electroplated to improve their appearance and resistance to corrosion.
Describe how metal electroplating occurs
(a) What is at the anode :
(b) What is at the cathode :
(c) What is used as the electrolyte :
(a) At the anode: The metal used to plate the object.
(b) At the cathode: The object being plated.
(c) Electrolyte: A solution containing ions of the metal being plated is used. Eg: CuSO₄ for copper electroplating
What is a Hydrogen Fuel Cell ?
A hydrogen–oxygen fuel cell uses hydrogen and oxygen to produce electricity with water as the only chemical product
Advantages and Disadvantages of a Hydrogen Fuel Cell
(List 4 of each)
Advantages
- Cleaner Emissions: Reducing air pollution.
- Higher Efficiency: Convert fuel to electricity more efficiently
- Renewable Energy Source: Hydrogen is renewable
- Quieter Operation: reduced noise pollution.
Disadvantages
- Limited Infrastructure: Lack of hydrogen refueling stations
- Cost of Production: hydrogen production is costly
- Storage Challenges: Requires specialized storage facilities
- Safety Risks: Hydrogen is highly flammable
