C3.4 - Electrolysis Flashcards
What is electrolysis?
Electrolysis is a process in which an electric current is passed through a compound, causing a chemical change.
What three components do you need for electrolysis to work?
- An electrolyte.
- Two electrodes.
- An electrical supply such as a power pack or
battery.
What is an electrolyte?
An electrolyte is a compound in its liquid state or in solution which contains mobile ions and conducts electricity.
What are electrodes?
- Electrical conductors used in electrolysis.There are two electrodes used in electrolysis:
- The negative electrode - The cathode
- The positive electrode - The anode.
What happens during electrolysis?
- Positive ions (cations) gain electrons at the
cathode and become atoms - They become
discharged. - Negative ions (anions) lose electrons at the anode
and become atoms - They become discharged. - If the atoms formed are non-metal atoms, covalent
bonds may form between them, making
molecules.
What is a binary ionic compound?
A binary ionic compound contains just two elements.
Explain how diffusion and convection occurs in electrolysis.
- Ions move to an oppositely charged electrode
during electrolysis. - The concentration of ions close to each electrode
goes down as ions gain or lose electrons to
become atoms. - Other ions in the electrolyte can move to replace
them by diffusion and convection. - Cannot happen which ionic compounds in the
solid state and therefore cannot conduct
electricity.
What are inert electrodes and what are they usually made from?
- Inert electrodes are not changed during
electrolysis. - Usually made from unreactive metals such as
copper or platinum, or from graphite. - Inert electrodes can be used for the electrolysis
of many ionic compounds in their liquid state or
in aqueous solution.
What happens during the electrolysis of water?
Water is naturally partially ionised - It contains small concentrations of hydrogen ions and hydroxide ions.
At the cathode hydrogen ions are discharged - Reduced as they gain electrons - Producing hydrogen in the gas state.
At the anode hydroxide ions are discharged - Oxidised as they lose electrons - Forms water and oxygen.
What are the ionic equations for the reactions with hydrogen ions at the cathode and hydroxide ions at the anode?
- 4H+ (aq) + 4e- -> 2H2 (g)
- 4OH- (aq) -> 2H2O (l) + O2 (g) + 4e-
How do you know what gets discharged as the cathode and anode during the electrolysis of an solution?
- Hydrogen is produced at the cathode, but if ions
from a less reactive metal than hydrogen are
present, they are discharged more easily and
therefore that metal is produced instead. - Oxygen is produced at the anode, but if ions from
an element in Group 7 are present at a high
enough concentration, the Group 7 element is
produced instead.
What is electroplating?
- Coating an object with a metal by electrolysis.
- Type of electrolysis that uses non-inert electrodes.
What are non-inert electrodes?
Electrodes that are changed during electrolysis.
Describe the things in electroplating?
- The cathode is the object you want to coat.
- The anode is a piece of metal you want to coat
the object with. - The electrolyte is a solution containing ions of
the coating metal.
How does electroplating work?
- Metal ions from the electrolyte are discharged on
the surface of the object (the cathode). - These ions are replaced by metal ions leaving the
surface of the anode. - Overall, metal leaves the anode and is deposited
on the object. - The process continues until the anode is used up.
