Chemical Changes Flashcards
What is Oxidation simple?
A reaction were oxygen is added to an element of a compound
What is reduction simple?
A reaction where oxygen is removed from an element of a compound
Example of an oxidation reaction
2Cu + O2 –> 2CuO
Example of a reduction reaction
ZnO + C –> Zn + CO
Zinc atom reduced, Carbon atom oxidised
What is the reactivity series?
A series of metals and some non-metals determining their ranks in reactivity
State the reactivity series -
Potassium, sodium, lithium, calcium, magnesium, aluminium, carbon, zinc, iron, tin, lead, hydrogen, copper, silver, gold
What is the mnemonic for the reactivity series?
Please Stop Loudly Calling Me A Careless Zebra Instead Try Learning How Copper Saves Gold
Why are carbon and hydrogen on the reactivity series?
They are very useful in extracting metals from their oxides by reduction processes
Which metals react with water?
Metals ABOVE HYDROGEN in the reactivity series react with water, eg.
Ca + 2H2O –> Ca(OH)2 + H2
What happens when acids and metals react?
The metal atom REPLACES the hydrogen atom in the acid to produce a salt and a hydrogen gas, eg.
Fe + 2HCl –> FeCl2 + H2
What determines the reactivity of the metal?
Its tendency to form ions, (ie. lose electrons)
How can carbon be used as a reducing agent?
To remove oxygen from metal oxide ores.
By placing carbon in the reactivity series, it allows us to see whether a metal oxide can be reduced or not by carbon
Metals BELOW carbon in the reactivity series can be extracted by heating the OXIDE with CARBON
Metals HIGHER than carbon have to me extracted by other methods, such as ELECTROLYSIS
How does the displacement of the reactivity series work?
A more reactive substance will DISPLACE a less reactive substance from its compounds, eg.
Zn + CuO –> ZnO + Cu
How can we visually see what displacement looks like?
New compounds of different metals often have different colours, eg.
Mg + CuSO4 –> MgSO4 + Cu
The blue colour of the CuSO4 FADES as the Mg displaces the Cu from the compound, to make a colourless MgSO4 solution + Cu
How can oxidation and reduction be represented in terms of their ELECTRONS?
Through ionic equations and HALF EQUATIONS
What happens when an electric current is passed through a molten ionic compound or aqueous solutions of ionic compounds?
The compound decomposes or breaks down into simpler structures
What are electrolytes?
Liquids and solutions that are able to conduct electricity
What is an electrolytic cell?
The set-up of the equipment for electrolysis. The equipment is as follows -
- Electrode
- Electrolyte
- Anode
- Anion
- Cathode
- Cation
What is an electrode?
A rod of metal or graphite through which an electric current flows into or out of an electrolyte
What is the electrolyte?
An ionic compound in a molten or dissolved solution that conducts the electricity
What is an anode?
The positive electrode of an electrolysis cell
What is the cathode?
The negative electrode of an electrolysis cell
What is an anion?
The negative ions which is attracted to the anode
What is a cation?
The positively charged ions which are attracted to the cathode
Why can’t ionic compounds in a solid state conduct elecricity?
They have no free ions that can move and carry the charge. Therefore an ionic compounds must be in a molten state or dissolved in a solution so the charge can pass through
What happens when the electrolytic cell is turned on?
An electric current is passed through an electrolyte, and the ions in the solution start to move towards the electrodes
What is produced at the anode?
The NON-METAL
What is produced at the cathode?
The METAL
What are the downsides of electrolysis?
Very expensive to provide the large amounts of energy to melt the ores and produce the electrical current
How is aluminium extracted from bauxite?
Bauxite is purified to produce aluminium oxide
Al2O3 has a very high melting point so it is first dissolved in molten cryolite producing an electrolyte with a lower melting point and a better conductor of electricity - THIS SAVES ENERGY AND MONEY AND MAKES THE PROCESS MORE EFFICIENT
The electrolyte is the solution of aluminium oxide in molten cryolite at a temperature of about 1000°C
Fresh aluminium oxide is added to the cell, where it operates at 5-6 volts and with a current of 100,000 amps
The heat generated by the huge current keeps the electrolyte molten
Oxygen is produced at the cathode, and sometimes reacts with graphite, (carbon) electrode to produce CO2 gas, meaning the carbon anode burns away, so they must be replaced regularly.
The molten aluminium sinks to the bottom of the cell and is gathered at the end of the extraction
What happens to water molecules during electrolysis of an aqueous solution?
Water molecules DISSOCIATE, producing H+ ions and OH- ions
During electrolysis of an aqueous solution, what goes to the anode?
Negatively charged OH- ions and negative non-metal ions
What is discharged at the anode?
Oxygen gas will be produced unless the ionic compound contains HALIDE IONS in which case the HALOGEN will be produced
What happens at the cathode during electrolysis of an aqueous solution?
Positively charged H+ ions and metal ions are attracted to the cathode but only one will gain electrons. Either HYDROGEN GAS or the METAL will be produced.
If the metal is ABOVE HYDROGEN in the reactivity series, then HYDROGEN WILL BE PRODUCED and bubbling will be seen at the cathode - this is because the more reactive ions will remain in solution, causing the least reactive ion to be discharged.
If the metal is BELOW hydrogen in the reactivity series, then the METAL is produced
REQUIRED PRACTICAL
TING
What do half equations represent?
The loss or gain of electrons within substances
How can we create ionic equations from half equations?
By combining the half equations and cancelling out the electrons
