Chapter C6 Electrolysis Flashcards
What does electrolysis mean?
Breaking down using electricity
What do you do in electrolysis?
Use a current to break down an ionic compound
What is the compound called that is broken down in electrolysis?
The electrolyte
What is the posture electrode called?
Anode
What is the negative electrode called?
Cathode
What are electrodes commonly made from?
Unreactive substance
Such as graphite
Why are electrodes made from unreactive substances?
So electrodes do not react with the electrolyte or products made
What happens when the ions in electrolysis reach the electrodes?
Lose their charge and become elements
Who was the first person to work on electrolysis?
Michael faraday
Do ionic compounds conduct electricity?
As a solid- no as their ions are in fixed positions
As a liquid- yes as the ions can move towards the electrodes
Can covalent compounds undergo electrolysis?
Only if they from ions when reacting with water
What is a half equation?
An equation that describes reduction or oxidation
Do a half equation for the electrolysis of Pb
Pb—-> 2E- + pb^2+
Complete the half equation for electrons being removed from negative ions for Br
2br- - 2e- ——> br^2
Why is electrolysis more complicated in aqueous solutions?
Because of the ions formed by water as it ionises
What happens at the anode in the electrolysis of aqueous solutions?
Oxygen gas is given off and hydroxide ions are discharged
What happens when a Solution contains a large concentration of halide?
Forms a halogen
What happens if two elements can be formed at an electrode?
The less reactive one will be formed
What is the compound electrolysed when performing electrolysis on aluminium?
Aluminium oxide
What is the ore of aluminium?
Bauxite
Describe the process of electrolysis of aluminium oxide?
The aluminium oxide requires free moving ions but the pure melting of it is very high 2050C.
So mix it with cryolite, and it melts at 850C
Aluminium forms on the cathode
Oxygen forms at the anode
What is the equation that results in the product of aluminium oxide?
Aluminium oxide
——> electrolysis ——>
aluminium +oxygen
What is brine?
Concentrated sodium chloride solution
What is produced from electrolysis of brine?
Chlorine gas (anode) Hydrogen gas (cathode) Sodium hydroxide
Half equation for anode of brine?
2CL-
—-> electrolysis
Cl^2 + 2e-
When electrolysis of brine occurs, why doesn’t sodium form at the cathode?
As hydrogen is the less reactive element and so if formed, whilst sodium remains in the aqueous solution
How do you test the solution at the cathode?
Acid base indicator
With electrolysis of aluminium oxide, why must the anode be regularly replaced?
As oxygen reacts with the graphite (carbon) to make carbon dioxide
Problems with electrolysis?
Is expensive
To melt the ionic compounds requires lots of bond energy
A lot of energy is required to produce the electric current
Process of aluminium electrolysis
Add aluminium to cryolite
Melts at 850C
Put carbon anode in water- the aluminium ions will go to the cathode, turning into aluminium atoms, whilst oxygen will be produced at the anode. This oxygen will wear at the anode, which is made of graphite, resulting in the formation of carbon dioxide. This means the anode will slowly get used up in the reaction and so must be replaced. A siphon is then used to collect the aluminium atoms
What are the products of sodium chloride in electrolysis
Sodium hydroxide
Chlorine
Hydrogen
What are the products if sodium sulfate in electrolysis
Hydrogen and oxygen
What are the products of copper chloride in electrolysis
Chlorine gas
Copper
What are the products of copper sulfate in electrolysis
Copper
Oxygen gas
Test for hydrogen gas
Squeaky pop
Test for oxygen
Glowing splint
Test for chlorine gas
Bleaches damp litmus paper
