extra questions - C6
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Why should a teacher demonstrate the electrolysis of molten lead bromide in a fume cupboard?
Toxic/poisonous fumes
Explain the difference between the processes in electrolysis and in a chemical cell.
• electrolysis uses electricity to produce a chemical • cells use chemical reactions to produce electricity
During electrolysis, some of the copper produced did not stick to the negative electrode but fell to the bottom of the beaker. Suggest how the students could find the total mass of copper produced.
• filter the mixture • wash and dry the copper • weigh the copper collected • add to the increase in mass of the electrode
Copper nitrate solution is blue. Suggest why the blue colour of the copper nitrate solution fades during the electrolysis.
The copper ions are discharged from the solution
Why do positive ions move towards the negative electrode
The electrode attracts ions of the opposite charge
Suggest two possible problems with storing the waste material from the bauxite in lakes of mud.
• danger of dam bursting • visual pollution
A student investigated the electrolysis of copper chromate solution. Explain why the colour changed at the positive electrode
• chromate ions moved to the positive electrode • because opposite charges attract
Does oxidation happen at the anode or cathode
anode
does reduction happen at the anode or cathode
cathode
half equation for the discharge of bromide ions
2Br- -> Br2 + 2e-
what is the pH of sodium hydroxide solution
13
Describe what happens at the negative electrode of molten zinc chloride
because zinc ions gain electrons 2 (electrons) zinc is formed
Explain, in terms of bonding, why pure water does not conduct electricity.
because (pure) water is covalent therefore (pure) water has no free ions
Why do alkaline batteries eventually stop working?
a reactant is used up
Why can alkaline batteries not be recharged?
the reaction is not reversible
Explain why magnesium chloride must be molten or dissolved in water to be electrolysed.
because ions can move, carry charge