Electrolysis Flashcards
(25 cards)
What are electrolytes?
Ionic compounds that are in the molten
state (heated so they become liquids), or
dissolved in water
What is electrolysis
Electrolysis is a process in which electrical energy, from a direct current (dc) supply, breaks down electrolytes
What is the negative charged electrode in electrolysis called
Cathode Positively charged ions move towards the Cathode
What is the positive charged electrode called
Anode Negatively charged ions move towards the anode.
Molten lead bromide, PbBr2(l), is an electrolyte. During electrolysis:
Pb2+ ions gain electrons at the cathode and become Pb atoms
Br- ions lose electrons at the anode and become Br atoms, which pair up to form Br2 molecules
Example
Predict the products of electrolysis of molten calcium chloride.
Positively charged calcium ions move to the negative electrode. Here, they gain electrons to form calcium atoms, so calcium is formed at the negative electrode.
Negatively charged chloride ions move to the positive electrode. Here, they lose electrons to form chlorine atoms. The atoms join up in pairs to form Cl2 molecules, so chlorine gas is formed at the positive electrode.
Example 2:
Predict the products of electrolysis of molten aluminium oxide.
Aluminium will form at the negative electrode and oxygen will form at the positive electrode.
What is dissociation
The breaking up of a molecule into ions when dissolved in water.
What are H+ ions attracted to
to the cathode, gain electrons and form hydrogen gas
What are OH- ions attracted to
attracted to the
anode
, lose electrons and form oxygen gas
An electrolyte formed by dissolving an ionic compounds contain
Hydrogen ions from the water, and positive ions from the compound
hydroxide ions from the water, and negative ions from the compound
Whether hydrogen or a metal is produced at the cathode depends on the position of the metal in the metal
reactivity series
:
the metal is produced at the cathode if it is less
reactive
than hydrogen
hydrogen is produced at the cathode if the metal is more reactive than hydrogen
Question: Predict the product formed at the negative electrode during the electrolysis of sodium chloride solution.
Hydrogen will be produced because sodium is more reactive than hydrogen.
Question: Predict the product formed at the negative electrode during the electrolysis of copper chloride solution.
Copper will be produced because copper is less reactive than hydrogen.
What is a half equation?
A half equation is used to represent the reaction that happens at an electrode during electrolysis
In half equations
electrons are shown as e- the numbers of atoms of each element
must be the same on both sides
the total charge
on each side must be the same (usually zero)
Name some half equations at the cathode
Na+ + e- → Na
Pb2+ + 2e- → Pb
2H+ + 2e- → H2
Example
Balance the half equation for the formation of aluminium during electrolysis: Al3+ + e- → Al.
The balanced half equation is: Al3+ + 3e- → Al (because three negatively charged electrons are needed to balance the three positive charges on the aluminium ion).
Write a balanced half equation for the formation of calcium from a calcium ion, Ca2+.
Ca2+ + 2e- → Ca
Name some half equations at the anode
2Cl- → Cl2 + 2e-
2O2- → O2 + 4e-
Write a balanced half equation for the formation of oxygen from hydroxide ions.
4OH- → 2H2O + O2 + 4e-
Write a balanced half equation for the formation of bromine, Br2, from bromide ions, Br-.
2Br- → Br2 + 2e-
What is Oxidation
loss of electrons
What is Reduction
gain of electrons
