C2.5 Salts And Electrolysis Flashcards
What pH is neutral?
pH 7
Give an example of an acid at pH 1
Battery acid
Give an example of an alkali at pH 14
Bleach
Oven cleaner
What two methods test for pH? What’s more useful?
Universal indicator
Litmus paper
Universal indicator is more useful because it shows you a specific colour so you can tell whether it’s a weak or strong acid/alkali
What’s an ion?
A charged particle
Fill in the gaps:
When metal atoms lose electrons, they form ________ ions.
When non-metal atoms gain electrons they form ________ ions.
- Positive
2. Negative
What’s an acid?
Somethings that forms H+ ions when added to water
What’s an alkali?
It forms hydroxide ions, OH- , when added to water
What’s a base?
Anything that neutralises acids but can’t dissolve in water
What’s the difference between an alkali and a bass?
They both neutralise acids but bases can’t dissolve in water whereas alkalis can.
What does ‘aq’ mean?
A solution - something dissolved in water
Copper oxide + sulphuric acid ->
Copper sulphate + water
Acid + alkali (base) ->
Salt + water
Acid + metal ->
Salt + hydrogen
Acid + metal carbonate ->
Salt + water + carbon dioxide
Hydrochloric acid + copper ->
Copper chloride + hydrogen
Calcium carbonate + sulphuric acid ->
Calcium sulphate + water + carbon dioxide
What happens when two soluble salts are reacted together?
Makes an insoluble salt
What’s the ionic equation for neutralisation?
H+(aq) + OH-(aq) -> H2O(l)
Acid + alkali -> water
Define electricity (in chemistry terms)
Flow of charge
Define electrolysis
Using electricity to separate ionic compounds
What ions are attracted to the cathode?
What ions are attracted to the anode?
- Positive
2. Negative
When you use electrolysis to separate copper chloride what would you see at the positive electrode? Negative electrode?
Positive electrode- bubbles of green/yellow gas (chlorine)
Negative electrode- copper coloured solid
What’s the name of the negative electrode?
Cathode
What’s the name of the positive electrode?
Anode
Positive ions are _______ - they ______ electrons
Negative ions are ______ - they _____ electrons
Reduced
Gain
Oxidised
Lose
What does OILRIG stand for 😌
Oxidation Is Loss (of electrons)
Reduction Is Gain (of electrons)
What’s the half equation for sodium chloride (NaCl)
Na+ + e- -> Na
2Cl- -> Cl2 + 2e-
What are the products when you electrolyse brine?
What do we use them for?
Chlorine - swimming pools
Hydrogen - fuels
Sodium hydroxide - cleaning substances
What is brine?
Salt water
Sodium chloride dissolved in water
When you look for the products of electrolysis what products come first on the cathode?
Metals below hydrogen Then Hydrogen Then Metals above hydrogen
When you look for products of electrolysis what comes first on the anode?
Halogens (group 7) Then Hydroxide (oxygen) Then All other negative ions
When you electrolysis of copper sulphate what do you see at the negative electrode? Why?
Copper is attracted to the cathode because copper ions are positive so they’re attracted to the negative electrode as opposites attract. The copper ions become neutral which form atoms as the copper gained two electrons. Copper ions are reduced and it becomes an atom which means it becomes solid
When you use electrolysis to separate copper sulphate what do you see at the positive electrode? Why?
The anode generates bubble around it and produces oxygen because the hydroxide which are negative to the positive electrode. It’s oxidised as it loses electrons and it becomes neutral meaning oxygen is produced which evaporates meaning bubbles are formed
What happens during electroplating?
The negative electrode is the object that is to be electroplated
The positive electrode is the metal you want to coat the object with
The electrolyte should be a solution of the coating metal such as its metal nitrate or sulphate
How do you plate a metal spoon in silver?
The metal spoon is connected to the negative terminal of the power supply. A piece of silver is connected to the positive terminal. The electrolyte is silver nitrate solution. The spoon is then coated in silver.
Why is electroplating useful?
Gives the object a protective layer - resistant to corrosion
Looks nicer (jewellery)
Cheaper to coat an object in gold/silver than the whole object being made of the metal
When we extract aluminium, why does aluminium oxide have to be molten?
So the ions can move freely and separate easily to the electrodes
Why is cryolite added when we extract aluminium?
To lower the melting point - less energy uses - cheaper
When you extract aluminium why do you have to regularly replace the carbon anodes?
They react with the oxygen and create carbon dioxide which wears the anodes away
What are the half equations for aluminium oxide (Al2O3)?
Al3+ +3e- -> Al
2O2- -> O2 + 4e-
