Electrolysis Flashcards
Electrolysis means ….
when you pass an electric current through a molten or dissolved ionic substance
What happens when you pass an electric current through a molten ionic substance or an ionic solution?
The solution breaks down into the elements it’s made of.
What does electrolysis require?
A liquid to conduct the electricity, called electrolyte
What do electrolytes contain?
What do these do?
Free ions usually in the molten or dissolved ionic substance
Conduct the electricity
For an electrical circuit to be complete there has to be what?
So electrons are taken away from where?
Where are they given to?
As ions gain or lose electrons what happens to them?
A flow of electrons
The negative electrode, cathode
Positive electrode, anode
They become atoms or molecules and are released
Reduction is …
So in electrolysis reduction is the …. of …
gain
gain of electrons
Oxidation is …
So in electrolysis oxidation is the …. of …
loss
loss of electrons
Electrolysis always involves either what or what?
Oxidation or reduction
What happens during the electrolysis of molten lead bromide?
- What happens at the -ve electrode
- What happens at the +ve electrode
- At the -ve electrode one lead ion accepts two electrons and becomes one lead atom
- Two bromide ions lose one electron each and become one bromide molecule, Br2
…. ions are attracted to the -ve electrode. Here they … electrons
Lead is produced at the … electrode
+ve, gain
-ve
…. ions are attracted to the +ve electrode. Here they … electrons
Bromine is produced at the … electrode
-ve, lose
+ve
Reactivity does what in electrolysis? (simple)
affects the products formed by electrolysis
Sometimes there are what in the electrolyte?
At the -ve electrode (cathode) where … ions gather because they have a …. charge, if there are … ions present the metals ions might do what? Why?
other free ions, like H+ ions and OH-.
metal, +ve, H+
Stay in the solution, because the H+ ions might be less reactive and so the reactive metal is more keen to stay as an ion. So Hydrogen will be produced unless the metal is less reactive.
At the +ve electrode (anode) where … ions gather because they have a …. charge, if there are … ions and …. ions present the molecules of …, … or … might do what?
If none of these three or their group is present, what will form here?
-ve, -ve, OH- and halide ions
chlorine, bromine, iodine might form.
Oxygen
What are the products of sodium chloride solution after electrolysis? (3)
Hydrogen, chlorine and sodium hydroxide
What happens and is then produced at the -ve electrode during the electrolysis of sodium chloride solution?
Two hydrogen ions accept two electrons and become one hydrogen molecule
What happens and is then produced at the +ve electrode during the electrolysis of sodium chloride solution?
Two chloride ions lose their electrons and become one chlorine molecule
What happens to the sodium ions during the electrolysis of sodium chloride solution?
They stay in the solution because they are more reactive than hydrogen
Hydroxide ions from water are also left behind as H+ is produced at the anode. So the OH- join to the sodium to form NaOH in the solution
Anode is where the …. goes as it is…. +ve
Cathode is where the … goes as it is…. -ve
non-metal
metal
What do half equations show?
What are the half equations for sodium chloride?
Write the atom and what happens with the electrons and what the product is at 1. the -ve, then 2. the +ve
The reactions at the electrodes
- 2H+ +2e- = H2
- 2Cl- = Cl2 + 2e-
What are the useful products from the electrolysis of sodium chloride solution?
- Chlorine - production of bleach and plastics
2. Sodium hydroxide - a strong alkali used widely in the chemical industry, soap
Aluminium is very …. but is always found naturally in ….
It’s main ore is …, after mining and purifying it … … is left
This is pure ….., what is the chemical formula for this?
How is it extracted?
abundant, compounds
white powder
Aluminium oxide, Al2O3
Electrolysis
What is the melting point of aluminium oxide? So what’s the problem
What happens to the aluminium oxide instead?
So now the temperature it’s melted at has been reduced to … which is what and what?
Over 2000 degrees, melting it would be very expensive
It’s dissolved in molten cryolite (less common aluminum ore)
900 degrees, cheaper and easier to reach
In the electrolysis of aluminium oxide what are the electrodes made of? Which is a ….
Carbon (graphite), good conductor of electricity
What does the diagram of the electrolysis of aluminium oxide look like? The anode: The cathode: On top of the electrolyte, a layer of: Electrolyte layer: The product at the cathode layer:
Rods of graphite stick into the mixture, all connected with a positive charge. The positive electrode
Carbon lining (graphite) of the vat has a negative charge as the cathode, the negative electrode
…crust
Molten bauxite in cryolite
A layer of molten aluminium
What are the half equations for the electrolysis of aluminium?
N= Al3+ + 3e- = Al P= 2O2- = O2 + 4e-
What forms at the cathode and the anode in the electrolysis of aluminium?
What then is formed for one of them meaning what?
Cathode- aluminium
Anode - oxygen
The oxygen reacts with the carbon electrode to form CO2 meaning the positive electrode gradually gets eaten away, and now need to be replaced every now and again which is expensive
What is electroplating and what does it do?
Uses electrolysis to coat the surface of one metal with another meta, e.g silver onto a brass cup for decoration
What is the negative electrode when electroplating?
What is the positive electrode when electroplating?
What will the electrolyte contain? So what does that mean about the plating ions?
The metal object to be plated
The pure metal that will be plating
Ions of the plating metal
The +ve electrode keeps the solution topped up, when the solution atoms are the ones to be plating the object
Give an example of electroplating a brass cup with silver:
What is the +ve electrode?
What is the -ve electrode?
What is the electrolyte?
Pure silver strip
Brass cup
Silver nitrate solution - Ag+, NO3 (-) little minus sign, lower sitting 3, not 3-
What are the uses for electroplating?
2 - examples and why
Decoration - silver is attarctive but very expensive so it’s cheaper to coat a cup than make it solidly out of it, it looks the same (think about solid gold’s properties)
Conduction- metals like copper conduct electricity well so they are often used to plate metals for electronic circuits and computers
