Oxidation, Reduction, Redox reactions. Flashcards
Oxidation/ reduction in terms of electrons.
OIL, RIG
Oxidation is loss
Reduction is gain
Ca + 1/2O2 –> CaO
What is being oxidised and what is being reduced in this reaction and why?
What is the reducing AGENT and what is the OXIDISING AGENT in this reaction?
- Ca goes from oxidation state of 0 to +2, it loses electrons so, it is oxidised.
- 1/2O2 goes from oxidation state of 0 to 2-, it gains electrons so, it is reduced.
- Reducing agent: Ca
- Oxidising agent: O2
What is a reduing/ oxidising agent?
- Reduing agent: electron donors, lose electrons - are oxidised themselves.
- Oxidising agent: electron acceptors. gain electrons - are reduced themselves.
What oxidation state do elements (on their own) have?
ie. O2/ Ca/ Cl2
- 0.
What oxidation state does H have - including the exception?
- +1.
- Exception: when the H is in hydrides ie. NaH (hydrides are when H is bonded to any metal), charge will be -1 here!
True or False
Group 1 and group 2 elements in compounds will always have oxidation states of +1 and +2.
- True.
- Group 1 and group 2 elements in compounds will always have oxidation states of +1 and +2.
What is a hydride?
- Hydride is H bonded to any metal (ie. NaH.)
What is the oxidation state of chlorine, when it is in a compound? Including the exception.
-1
- Exception: except in compound with F and O, it would have a positive value.
In ClF3, what is the oxidation state of the Cl and why?
- +3
- Fluorine = higher up in hierarchy for assigning oxidation states, so you assign its oxidation state before Cl.
True or False
Fluorine’s charge/ oxidation state will change depending on what compound it is in.
- False.
- Fluorine’s charge/ oxidation state is always -1.
What oxidation state does oxygen have in compounds? Including the exceptionSSS.
- 2-
- ExceptionSS : in peroxides/ when bonded to F.
Why does O have oxidation state of +2 in OF2?
- Because fluorine is more is higher up in the “assigning oxidation states” hierarchy than oxygen, so takes the negative charge/ oxidation state rather than oxygen.
What oxidation state does O have in H2O2?
-1.
What oxidation state/ charge will aluminium ALWAYS have when it is in a compound?
+3
What oxidation state does S have in H₂SO₄? Show workings.
- H = +1 charge. (2x +1) = +2.
- O (most electronegative) has oxidation state of 2-. 4 x 2- = -8.
- Need +6 for charges to balance so, S = oxidation state of +6.
What oxidation state does S have in SO₄²⁻ ? Show working.
- O = -2 charge. (4 x 2-) = -8.
- Whole molecule is 2- so S must have charge/ oxidation state of +6.
What must all the oxidation states in a compund add to?
- All the oxidation states in compound must add up to the overall charge on the molecule.
What oxidation state does V have in VO²⁺?
- O has oxidation state/ charge of -2.
- V must have oxidation state/ charge of +4 , to make the overall charge +2.
What are the steps for balancing half equations?
- Balance any atoms (other than O and H.)
- Balance any oxygens using H2O.
- Balance any hydrogens with H+ ions.
- Balance charge using electrons (e-)
Write the half equation to show the conversion of MnO₄⁻ to Mn²⁺. Show all the steps.What does this equation show?
- Balance oxygens using water:
MnO₄⁻ –> Mn²⁺ + 4H₂O. - Balance any hydrogens with H+ ions.
MnO₄⁻ + 8H⁺ –> Mn²⁺+ 4H₂O - Balance the charge.
MnO₄⁻ + 8H⁺ + 5e⁻–> Mn²⁺+ 4H₂O
SHOWS REDUCTION (don’t think that it is oxidation because the charge goes from -1 to +2, it’s not comaparable because they are two completely different species.)
These are two half equations in redox reaction.
Fe²⁺ –> Fe³⁺ + e⁻
MnO₄⁻ + 8H⁺ + 5e⁻ –> Mn²⁺ + 4H₂O
Write the overall ionic equation for this redox reaction/ steps to get to this stage?
- Make sure electrons are balanced.
- 5e- on bottom equation only 1 e- on top equation, so multiply top equation by 5.
- 5Fe²⁺ –> 5Fe³⁺ + 5e⁻
- Cancel out the electrons.
- Combine the two equations together:
5Fe²⁺ + MnO₄⁻ + 8H⁺ –> 5Fe³⁺ + Mn²⁺ + 4H₂O
What are redox reactions?
- When oxidation/ reduction are happening at the same time ie. in the same equation.
True or False
Ionic equations can contain electrons, the electrons just have to be balanced on either side of the equation
- False!!
- Ionic equations DO NOT contain electrons.
What order to we assign oxidation states in?
- Group I metals
- Group II metals
- Group 3 metals
- Fluorine: -1
- Hydrogen: +1 (except in metal hydrides.)
- Oxygen: -2 (except when bonded to F/ in a peroxide.)
F-ing HO (neumonic :))
