C2.7 Flashcards
What is electrolysis?
The breaking down of an ionic compound, making elements, using electricity
What is reduction?
When positively charged ions gain electrons at the negative electrode
What is oxidation?
When negatively charged ions lose electrons at the positive electrode
What do ions of less reactive elements do?
Accept electrons more readily
What is bauxite?
Aluminium ore
What is a redox reaction?
A chemical reaction in which both reduction and oxidation happen
Why must aluminium oxide be molten for electrolysis?
Because when it is molten the ions are free to move
What are the products of the electrolysis of sodium chloride solution (brine) used for?
~ Chlorine is used to kill bacteria in swimming pools, as disinfectant, and to produce plastics
~ Hydrogen is used to make ammonia and margarine
~ Sodium hydroxide is used to make detergents
Why is electrolysis used to electroplate objects?
~ Protects them from corrosion
~ Improves their appearance
When is electrolysis used to purify metals?
After they’ve been extracted from their ore
What needs to happen for copper to be purified?
~ The positive electrode needs to be made of impure copper
~ The negative electrode needs to be made of pure copper
~ The solution must contain copper ions
What electrode will the copper ions move to?
The negative electrode to gain electrons and form copper atoms which stick to the pure copper electrode and can be extracted
Why is cryolite used in aluminium extraction?
Because it lowers the melting point and allows electrolysis to be carried out at a lower temperature
Why do the electrodes need to be replaced in aluminium extraction?
Because as the oxygen reacts with carbon electrode, the electrode slowly disappears and needs to be replaced
Why do ionic compounds need to be molten or in solution to do electrolysis?
Because their ions need to be free to move to carry the electricity
In the electrolysis of sodium chloride, why is hydrogen produced at the negative electrode and not the sodium?
Hydrogen is less reactive than sodium
What are the products of the electrolysis of sodium chloride solution?
~ Chlorine gas at the positive electrode
~ Hydrogen gas at the negative electrode
~ Sodium hydroxide
Why is aluminium a useful metal?
~ Very strong
~ Very light
What does aluminium ore (bauxite) contain?
~ Aluminium ore
~ Impurities
Why can’t aluminium oxide be broken down by heating it with carbon?
Because aluminium is more reactive than carbon so it will hold on to the oxygen
What is the problem with melting aluminium oxide?
~ Aluminium melts at about 2000 degrees
~ Costs lots
~ Uses lots of energy
What is an electrolyte?
A substance that electrolysis is carried out on
What is done before lead bromide is broken down via electrolysis?
It’s heated
If the electrolyte contains a mixture of ions, the products formed depend on what?
The reactivity of the elements involved
How can aluminium be collected when extracting it?
It sinks to the bottom of the container because it’s more dense than the aluminium oxide and cryolite mixture
Why is carbon dioxide produced from the electrolysis of aluminium oxide and cryolite?
~ Oxygen forms at the positive electrode
~ The positive electrode is made of carbon which reacts with the oxygen, producing carbon dioxide
What is a test for chlorine?
It bleaches damp litmus paper (removes the colour)
