Chapter 12 - Oxidation and Reduction Flashcards
What is a redox reaction?
A redox reaction is a chemical reaction which involves oxidation and reduction simultaneously
What are the 4 ways to define oxidation?
Oxidation is the
- gaining of oxygen
- loss of hydrogen
- loss of electrons
- increase in oxidation state
What are 4 ways to define reduction?
Reduction is the
- loss of oxygen
- gaining of hydrogen
- gaining of electrons
- decrease in oxidation state
Why does rusting happen?
Iron undergoes a process called oxidation. Under the right conditions, iron will react with oxygen. As more oxygen reacts with iron, the iron gets converted from silvery iron metal to black and then red-brown iron compounds
State the rusting of iron balanced equation
When iron rusts, it reacts with oxygen to give hydrated iron (III) oxide shown by this equation:
4Fe + 3O2 + 2xH2O –> 2Fe2O3.xH2O
How is rusting reversed?
Iron is found in a mineral (haematite), which is mostly iron (III) oxide, Fe2O3. It can be extracted as a blast furnace by reacting with carbon monoxide. This causes iron (III) oxide to be reduced back to iron, losing all its oxygen
State the balanced equation of reverse of rusting
Fe2O3 + 3CO –> 2Fe + 3CO2
In this reaction, iron (III) oxide loses oxygen to become iron, but carbon monoxide gains oxygen to become carbon dioxide. So oxidation and reduction takes place at the same time
In, S + O2 –> SO2, which one is oxidised?
S gains oxygen, so S is oxidised
In, 2CuO + C –> 2Cu + CO2, which one is reduced?
CuO loses oxygen, so CuO is reduced
When deducing whether something has been oxidised or reduced, we look at the ____
Reactants
What is the equation for burning of methane and which is oxidised?
CH4 (g) + 2O2 (g) –> CO2 (g) + 2H2O (g)
Methane gains oxygen and is hence oxidised. However, it also loses hydrogen.: by the time it becomes carbon dioxide, the carbon atom not only gained 2 oxygen atoms, but lost 4 hydrogen atoms
What is the overall equation for burning of hydrogen?
2H2 (g) + O2 (g) –> 2H2O (g)
Hydrogen gains oxygen and is oxidised to water vapour, oxygen gains hydrogen and is reduced to water vapour
In, 2HBr + Cl2 –> 2HCl + Br2, which one is oxidised?
HBr loses hydrogen, hence it is oxidised
In, 2HBr + Cl2 –> 2HCl + Br2, which one is reduced?
Cl2 gains hydrogen, hence it is reduced
When iron oxidises in the presence of oxygen and water to become rust, the iron atoms eventually become ____
Iron (III) ions/Fe^3+. The charge numbers on iron get larger as the iron atoms lose electrons and become ions
State the balanced chemical equation of iron atom losing electrons during rusting
Fe –> Fe^3+ + 3e-
Every iron atom in the reaction loses 3 electrons
If iron reacts with oxygen directly it will change from iron to ____
Iron (III) oxide. As iron oxidises, the oxygen gas becomes oxide ions
State the balanced chemical equation for rusting when iron loses electrons
O2 + 4e- –> 2O^2-
While iron loses electrons, the oxygen that reacts with it gains electrons
Which type of bonding does not involve oxygen, hydrogen or electron transfer?
Covalent bonding. This is why there is a more general definition of oxidation and reduction: oxidation state
What is the oxidation state?
The charge of an atom of an element would have if it is existed as an ion in a compound
Oxidation state can take on any positive or negative whole number or zero. True or false?
True
An increase in oxidation state (more +, less -) refers to the ____ of electrons and hence ____
Loss, oxidation
