C6-Electrolysis Flashcards
What does the word electrolysis mean?
Breaking down using electricity
What is the positive electrode called?
The anode
What is the negative electrode called?
The cathode
What are electrodes often made out of?
An unreactive substance such as graphite or platinum metal.
Movement of ions in electrolysis
Positively charged ions move to the cathode
Negative ions move to the anode
This is because opposite charges attract.
What is electrolysis used for?
Breaking down an ionic compound
Why do ionic compounds not conduct electricity when solid?
Because there ions are in fixed positions in their giant lattice. Ions are held in place by strong electrostatic forces of attraction
Why do ionic compounds conduct electricity when molten (melted)?
Because the ions are free to flow within the hot liquid as the forces of attraction are broken
What can be done to ionic compounds in order to allow them to conduct electricity if they have high melting points?
Some can be dissolved in water which will allow the ions to become free to move around
What do negatively charged ions do to become neutral?
Lose electrons
What to positively charged ions do to become neutral?
Gain electrons
What ions does water form?
H+ ions - Hydrogen ions
OH- ions - Hydroxide ions
If two elements can be produced at an electrode what will form?
The less reactive element will usually be formed
Order of discharge at the anode
Halide ion > Hydroxide > all other negatively charged ions
Uses of aluminium
Pans
Overhead power cables
Aeroplanes
Cooking foil
Drink cans
How can aluminium oxide be obtained?
It comes from the ore Bauxite which can be mined. The impurities such as iron oxide then have to be separated.
How can chemists save some energy when melting aluminium oxide?
The aluminium oxide is mixed with molten cryolite which creates a molten mixture which can be electrolysed at 850 degrees.
What are the products when brine (concentrated sodium chloride solution) is electrolysed?
Hydrogen gas at the cathode
Chlorine gas at the anode
Sodium hydroxide solution
Half equation example: Chlorine loses two electrons
2CL- - 2e- > Cl2
In electrolysis how is charge supplied to the electrodes?
Using a power pack
Why must the anode be replaced regularly in the electrolysis of Aluminium oxide?
This is because the oxygen molecules produced at the anode react with the graphite (carbon), forming carbon dioxide gas
Why is electrolysis very expensive?
Melting the compounds such as aluminium oxide requires a great deal of energy
A lot of energy is required to produce the electric current
Why is platinum often used as an electrode?
It is an inert, uncreactive metal
Hydroxide ion half equation at anode
40H- - 4e- –> 02 + 2H20
How can pure metals be extracted from metal oxides?
Using electrolysis
Adding carbon to reduce the metal (remove oxygen)- This only works when the metal is less reactive than carbon
