C4: Chemical changes Flashcards
What is an ore
COMPOUND OF A METAL FOUND NATURALLY IN ROCKS IN EARTH’S CRUST
A rock containing enough metal to make it economical to extract the metal.
What is meant by OXIDISED?
GAINS oxygen, LOSE electrons
What is meant by REDUCTION?
LOSE oxygen, GAIN electrons
What is a displacement reaction?
A reaction where are more reactive metal takes the place of a less reactive metal in a compound.
Metal + oxygen->
Metal oxide
Metal +water->
Metal hydroxide + hydrogen
How can metals less reactive than carbon be extracted?
Reduction with carbon.
Carbon displaces the metal in the metal oxide and is oxidised to form carbon-oxides.
The metal from the metal oxide gets reduced to the pure metal.
What is a redox reaction?
A reaction where both oxidation and reduction occurs.
What is a cathode and what is an anode?
Cathode is the negative electrode, anode is the positive electrode
What occurs at the cathode and at the anode during electrolysis ?
REDUCTION at cathode
OXIDATION at anode (PANIC)
In aqueous electrolysis, who gets made at cathode and anode?
CATHODE- if the metal is more reactive than hydrogen, hydrogen is made. (And vise versa)
ANODE- is the metal is a halide (group7) the halogen gets made, otherwise oxygen is made.
How is aluminium manufactured.Why?
Aluminium is made through electrolysis. The main ore of aluminium is bauxite which contain aluminium oxide. This has a VERY high melting point and would be very expensive to melt it because of high energy demand.
Therefore, it is mixed with cryolite this reduces the melting point to about 950C.
Because Al is 3+ it is attracted to the negative electrodes in the cathode and will gain electrons.(this is produced as a liquid on the bottom)
Oxide ions are 2- so they are attracted to the anode where they lose electrons to form oxygen.
Oxygen reacts with the carbon(graphite) anode and produces CO2.
Write the half equations for the electrolysis of aluminium
Al3+ + 3e- —> Al
2 O2- —> O2 + 4e-
What does aqueous mean?
Dissolved in water
Who gets made in the electrolysis of aqueous NaCl ?
Write the half equations.
ANODE- hydrogen because sodium is more reactive
CATHODE- chlorine because it is a halide
2H(+) + 2e- —> H2
2Cl- —> Cl2 + 2e-
Why does the positive electrode have to be replaced at regular intervals? (4)
1) electrode is made from carbon
2) 02 is produced at anode
3) 02 reacts with carbon to form c02
4) needs to be replaced as carbon is lost.
REQUIRED PRACTICAL : Making soluble salts METHOD (6)
Describe a method to make pure, dry crystals of copper sulphate from a metal oxide and a dilute acid .
1)oxide and sulphuric acid
2)add sulphuric acid to beaker and heat it under a Bunsen burner
3)add copper oxide and stir (CONTINUE ADDING UNTIL COPPER OXIDE IS EXCESS)
4)Filter using filter paper in funnel to remove excess copper oxide
5)heat solution in evaporating basin to crystallisation point (after heating leave rest of water to evaporate slowly to give larger crystals)
6)leave to crystallise
REQUIRE PRACTICAL: ELECTROLYSIS
1)Add the aqueous solution to the beaker
2)Add two graphite rods as the electrodes/ put test tubes on electrodes and connect this to a power pack or battery
3)Turn on the power pack or battery and allow electrolysis to take place
4)Record the results in a suitable table and repeat for another solution, checking the electrodes in between runs to see if any metal has been deposited
5)The gases produced can be collected in the test tubes to be tested later
Acid + metal —>
Salt + hydrogen
Acid + metal oxide —>
Salt + water
Acid + metal hydroxide —>
Salt + water
Acid + metal carbonate—>
Salt + water + carbon dioxide.