Redox Flashcards
definition of oxidation (4)
- gain of oxygen
- loss of hydrogen
- loss of electrons
- increase in OS
definition of reduction (4)
- loss of oxygen
- gain in hydrogen
- gain in electrons
- decrease in OS
rules of assigning OS – in order (4 main, 9 in total)
- OS of free elements is 0 (unbonded elements)
- fixed OS
- fluorine always -1 (halogens)
- grp I, II, III usually +1 +2 +3 (when form ionic)
- oxygen usually -2, unless peroxide. superoxide
- hydrogen +1 (with non-metal), -1 (metal)
- simple ion –> charge of ions
- sum of OS in compound is 0
- sum of polyatomic = charge of ion
which takes priority when assigning OS, shells or proton number
shells (acts as blockage) then proton number
Why there is OS for covalent bond (eg CO₂)?
covalent -> no ions
- 2 diff types of NM, shared valence electrons tend to shift
- more proton, less electron shell -> attract electrons more strongly, pull them closer, ‘gaining’ electrons, having ‘partial charge’
how to see oxidation and reduction in chemical equation?
assign oxidation number / charge number
peroxide and superoxide charge?
O₂ ²⁻, O₂⁻
Practice!
Na₂S₄O6 -> S?
+2.5
Practice!
PCl₃ -> Cl?
-1
Practice!
PCl₅ -> Cl?
-1
Practice!
MnSO₄ -> Mn?
+2
Practice!
Fe₃(PO₄)₂ -> Fe?
+2
Practice!
Fe₃O₄ -> Fe
+2 2/3 or +2.67 (fine as a fraction)
range of OS grp I, II, III, IV, V, VI, VII
I +1 II +2 III +3 IV +4 to -4 V +5 to -3 VI +6 to -2 VII +7 to -1
OA RA
definition
OA oxidises other reactants but itself reduced
RA reduces other reactants but itself oxidised
OA (6)
name – spelling
formula + state
observation (colour change or reaction)
- Acidified potassium manganate (VII) KMnO₄ (aq) with H₂ SO₄ (aq) purp -> colourless
- hydrogen peroxide H₂ O₂ (aq) remains colourless
- potassium dichromate K₂Cr₂O₇ orange to green
- Cl₂ (g) light greenish-yellow -> colourless
- I₂ (s/aq) brown to colourless
- Fe³⁺ (aq) Fe₂ (SO₄)₃, FeCl₃, Fe(NO₃)₃, yellow -> light green
RA (5)
name – spelling
formula + state
observation (colour change or reaction)
- KI (aq) colourless to brown
- Fe²⁺ (aq) FeSO₄, FeCl₂ , Fe(NO₃)₂ , light green -> yellow
- sodium thiosulfate Na₂S₂O₃ (aq) remains colourless
- hydrogen peroxide H₂O₂ (aq) effervescence of colourless odourless gas (O₂ ) which relights glowing splint
- sulfite ion SO₃²⁻ (aq) and sulfur dioxide gas SO₂ (g) remains colourless
Template for answering redox qn
gain/loss of e
(substance) is oxidised/reduced because it has lost/gained electrons to form (substance)
eg Zn has been oxidised because it has lost electrons to form Zn ²⁺
Template for answering redox qn
increase/decrease in OS
(substance) is oxidised/reduced because the oxidation state of (element) has increased/decreased from (oxidation state) in (substance) to (oxidation state) in (substance)
eg 2 PbS + 3 O₂ -> 2 SO₂ + 2 PbO
O₂ has been reduced because the oxidation state of oxygen decreased from 0 in O₂ to -2 in SO₂ / PbO
Template for answering redox qn
OA RA
(statement explaining why substance is oxided/reduced). Since (substance) is oxidised/reduced, it is a oxidising/reducing agent.
eg Cl₂ + 2 KI -> 2 KCl + I₂
ionic = Cl₂ + 2 I⁻ -> 2 Cl⁻ + I₂
Cl₂ is an oxidising agent. Oxidation state of chlorine decreased from 0 in Cl₂ to -1 in Cl⁻
I- is a reducing agent. Oxidation state of iodine increases from -1 in I⁻ to 0 in I₂
Template for writing observations (OA RA)
colour change
The (colour) (name of chemical) solution turns (colour)
eg Cl₂ + 2 KI -> 2 KCl + I₂
ionic = Cl₂ + 2 I⁻ -> 2 Cl⁻ + I₂
observation: colourless potassium iodide solution turns brown I₂ (aq) with black solids I₂ (s)
Template for writing observations (OA RA)
gas
Effervescence of (colour)(odour) gas that (test for gas)
eg hydrogen peroxide H₂O₂ (aq)
Effervescence of colourless odourless gas which relights glowing splint. The gas is oxygen.
