C6 - Electrolysis Flashcards
What happens when an ionic compound is melted or dissolved in water
The ions are free to move about within the liquid or solution
Can an ionic compound which is melted or dissolved in water conduct electricty
Yes
What are ionic compounds which is melted or dissolved in water called
Electrolytes
What happens when you pass an electric current through electrolysis
causes the ions to move to the electrodes. Positively charged ions move to the negative electrode (the cathode), and negatively charged ions move to the positive electrode (the anode).
What is the negative electrode called (which positively charged ions move to)
The cathode
What is the positive electrode called (which negatively charged ions move to)
Anode
What do ions produce at the electrodes
Ions are discharged at the electrodes producing ELEMENTS
What is the process of passing an electric current through electrolytes and producing elements called
Electrolysis
What happens when a simple ionic compound (eg lead bromide) is electrolysed in the molten state using inert electrodes
the metal (lead) is produced at the cathode and the non-metal (bromine) is produced at the anode.
What can be extracted from molten compounds using electrolysis
Metals
When is electrolysis used for extraction instead on carbon
if the metal is too reactive to be extracted by reduction with carbon (higher than carbon on the reactivity series) or if the metal reacts with carbon.
Why is carbon used over electrolysis if possible
Expensive as large amounts of energy are used in the extraction process to melt the compounds and to produce the electrical current.
How is aluminium manufactured
by the electrolysis of a molten mixture of aluminium oxide and cryolite using carbon as the positive electrode (anode).
What do the ions discharged when an aqueous solution is electrolysed using inert electrodes depend on
the relative reactivity of the elements involved.
When is hydrogen produced at the negative electrode (cathode)
if the metal is more reactive than hydrogen
When is oxygen produced at the positive electrode (anode)
is produced unless the solution contains halide ions when the halogen is produced.
Why does the negative electrode (cathode) sometimes produce hydrogen and why does the positive electrode (anode) sometimes produce oxygen
because in the aqueous solution water molecules break down producing hydrogen ions and hydroxide ions that are discharged.
What are the reactions at the cathode during electrolysis
Reductions (positively charged ions gain electrons)
What are the reactions at the anode during electrolysis?
Oxidations (negatively charged ions lose electrons )
Reactions at electrodes can be represented by half equations, for example:
2H+ + 2e- → H2
Or 4OH- → O2 + 2H2O + 4e- or
Or 4OH- – 4e- → O2 + 2H2O
Why is aluminium oxide displaced in molten cryolite in the extraction of aluminium
This lowers the melting point to save energy during extraction
Calculate the maximum mass of aluminium metal that can be extracted from 25.5 tonnes of aluminium oxide
Al^2O^3 = (2x27)+(3x16)=54+48=102
No of moles = 25500000/102
2Al^2O^3 moles = 250000x2 =500000
500000 x 27 =13500000 = 13.5 tonnes
Why does the positive anode need to be continuously replaced
The carbon anodes gradually burn away and need to be replaced regularly
What will be the products of this molten ionic compound Zinc Chloride(l)
- > Zinc (Zn^2+ move towards cathode, the negative electrode) + chlorine (Cl- move towards anode, the positive electrode)
- > Zn(s/l) + Cl^2(g)
