C2.7 Electrolysis Flashcards
What happens when an ionic substance is melted or dissolved in water?
The ions are free to move about within the liquid or solution
What does passing an electric current through ionic substances that are molten do?
Breaks them down into elements
What is electrolysis?
The breaking down of substances into elements with electricity
What is the name of the substance broken down by electrolysis?
The electrolyte
During electrolysis, where do the positively charged ions move towards?
The negative electrode
During electrolysis, where do the negatively charged ions move towards?
The positive electrode
What is the name for the negative electrode?
The cathode
What is the name for the positive electrode?
The anode
What can electrolysis also be used to do?
Electroplate objects
What happens at the negative electrode?
Positively charged ions gain electrons (reduction)
What happens at the positive electrode?
Negatively charged ions lose electrons (oxidation)
If there is a mixture of ions, what does the products formed depend on?
The reactivity of the elements involved
What can reactions at electrodes be represented by?
Half equations
e.g. 2Cl- ===> Cl2 + 2e-
2Cl- - 2e- ===> Cl2
How is aluminium manufactured?
By the electrolysis of a molten mixture of aluminium oxide and cryolite
Where does aluminium and oxygen form?
At the negative electrode and oxygen at the positive electrode
What is the positive electrode made of during electrolysis of aluminium oxide and cryolite?
Carbon, it reacts with oxygen to form carbon dioxide
What does the electrolysis of sodium chloride solution produce?
Hydrogen, chlorine and sodium hydroxide
What can sodium hydroxide be used to make?
Soap
What can chlorine be used to make?
Bleach and plastics
Why is cryolite used?
To lower the temperature and therefore the costs
What happens in electroplating?
The negative electrode is formed of the metal object you wish to plate and the positive electrode is the pure metal you want it to be plated with. The electrolyte also needs to contain ions of the plating metal
What are the two main uses of electroplating?
Decoration (decorating cheaper metals with a coat of silver is much cheaper than using silver itself) and Conduction (plate metals with copper to conduct electricity)
At the cathode, if metal ions and H+ ions are present , the metal ions will stay in solution if the metal is…
More reactive than hydrogen
Hydrogen will be formed if the metal is…
More reactive than hydrogen
At the anode, if OH- and halide ions are present then…
Molecules of chlorine, bromine and iodine will be formed
If no halide is present then…
Oxygen will be formed
What is the main aluminium ore?
Bauxite
Oxidation is…
Loss
Reduction is…
Gain
