C3.4 - Electrolysis Flashcards
What is Electrolysis?
Decomposition of an ionic compound using electricity
What is an electrolyte?
A compound in its liquid state / a solution that has mobile ions / is able to conduct electricity.
What is an Electrode?
An anode / cathode - made from metals/graphite and are able to conduct electricity to the electrolyte
Cathode detention?
Negative electrode
Anode detention?
Positive electrode
What are the two rules for electrolysis of solutions?
- If the ions of a metal are more reactive than hydrogen, hydrogen will be produced at the cathode
- Oxygen is produced at anode, if there are no ions of group 7 present. If they are then the group 7 element is produced instead
What is less reactive than hydrogen ?
Copper, silver, gold, platinum
Group 7 elements ?
Fluorine, iodine, chlorine, bromine, astatine
Why are the electrodes made up of graphite?
- graphite is a conductor
- graphite is inert
What ions are attracted to what electeodes?
- Positively charged ions are attracted to the negative electrode ( cathode )
- Negatively charged ions are attracted to the positive electrode (anode )
Why is electrolysis important?
It enables us to isolate different elements and extract useful elements
What happens at the cathode?
Reduction - the ions gain electrons to form a full outer shell
What happens at the anode?
Oxidation - the ions lose electrons
Draw a diagram of electrolysis?
Yes :
Why is copper purified using electrolysis?
Since mining is a labour intensive and expensive alternative
What ions are involved in the electrolysis of a solution?
The ions of the compound, OH-, H+
For example : Explain how sodium bromide solution is separated?
Because it is a solution there ar H+ Ions a OH- ions present, as well as K+ and Br- ions. At the anode, which is positive, negative anions ( Br- and OH- )are attracted but since Br- is a halide ion it is discharged and OH- reminds in the solution. 2Br —> Br2 + 2e-. At the cathode which is negative, positive cations ( H+ and K+ ) are attracted but only hydrogen is discharged since potassium is more reactive than hydrogen so it remains in the solution 2H+ + 2e- —> H2 therefore hydrogen gas has formed.
What is the difference in electrolysis between molten and aqueous substances?
Molten substance don’t contains OH- or H+ ions whilst aqueous do
What is electroplating?
Electroplating uses electrolysis to put a thin layer of a metal onto a metal object
How is electrolysis used to purify copper?
You need a pure and impure copper rod for the anode and cathode as well as copper sulphate solution.
- at the anode, copper atoms lose electrons to form copper ions, which dissolved in a solution ( oxidation )Cu —> Cu2+ + 2e-
- At the cathode copper ion from the solution and impure, copper gain electrons to form a pure copper ( reduction ) Cu2+ + 2e- —> Cu
Why is the sludge as a result of copper purification kept and not thrown away?
Factories keep this instead of throwing it out since it may contain rare metals
Why do people/ factories electroplate objects/ products ?
- To protect them from harm, to protect them from reacting with the surroundings
- To make them look pretty/ give them an appealing look
- A cheap alternative to making the whole thing in that particular shiny metal/ or just metal in general
