4: Electrochemistry

electrolysis

the breakdown of an ionic compound, when molten or in aqueous solution, by the passage of an electric current

Simple electrolytic cells

the anode is the positive electrode (oxidation). Eg. 2Cl- -> Cl2 + 2e-
the cathode is the negative electrode (reduction) eg. Na + e- -> Na
the electrolyte is the molten or aqueous substance that undergoes electrolysis

Predicting products for halide compounds in dilute/concentrated solution

Cathode: the product is based on lower reactivity series
Dilute: Anode: hydroxide ion (which makes oxygen)
Conc: Anode: halide ion.

molten lead (Il) bromide

product (+)

bromine, Br,

observations (+)

bubbles of brown gas

product (-)

lead, Pb

observations (-)

grey metal coating

concentrated aqueous sodium chloride

product (+)
chlorine, Cla
observations (+)
bubbles of green gas
product (-)
hydrogen, H,
observations (-)
bubbles of colourless gas

dilute sulfuric acid

product (+)
oxygen, O,
observations (+)
bubbles of colourless gas
product (-)
hydrogen, H2
observations (-)
bubbles of colourless gas

Products of electrolysis

metals or hydrogen are formed at the cathode and that non-metals (other than hydrogen) are formed at the anode

Electroplating

metal objects are electroplated to improve their appearance and resistance to corrosion

Electroplating process

the cathode (-) is the object being plated
the anode (+) is the metal used to plate the object
the electrolyte is a solution containing ions of the plating metal

Transfer of charge

anions move to anode, anions (-) lose electrons , electrons flow from the anode to the cathode in the external circuit, cations move to cathode, cations (+) gain electrons

Aqueous copper (II) sulfate using inert carbon/graphite electrode

product (+)

oxygen, O2

observations (+)

bubbles of colourless gas

product (-)

Copper, Cu

observations (-)

pink metal coating

Aqueous copper (II) sulfate using copper electrode*

product (+)

n/a

observations (+)

solution remains blue (Cu2+ is replaced)

mass of anode decreases

product (-)

Copper, Cu

observations (-)

pink metal coating

Hydrogen-Oxygen fuel cells*

A hydrogen-oxygen fuel cell uses hydrogen and oxygen to produce electricity with water as the only chemical product.

Hydrogen + Oxygen -> Water

A of Hydron-Oxygen Fuel Cells

Only water formed, water not a pollutant
No carbon dioxide formed, more efficient

D

Challenges in Hydrogen Storage: Hydrogen is in a gaseous state at room temperature and pressure, making it difficult to store effectively in cars.

  Expensive: Fuel cells are expensive, contributing to higher overall costs of manufacturing and purchasing fuel cell vehicles.

  Limited Filling Infrastructure: There is currently no widespread network of hydrogen filling stations

  Environmental Impact of Hydrogen Production: while the vehicle itself emits no pollutants, producing the hydrogen fuel generates air pollutants.’