Redox Flashcards
What is oxidation?
The loss of electrons
What is reduction?
The gain of electrons
What is the reactant that is oxidised called?
Reductant/reducing agent
What is the reactant that is reduced called?
Oxidant/oxidising agent
What is the difference in how oxidation numbers and charges are written?
Oxidations numbers have the sign before the number, whereas charger have the number before the sign
Are oxidation numbers and charges equal?
Not necessarily, they can be but it isn’t always the case
What are the rules for oxidation numbers?
- When atoms exist as elements, they have an oxidation number of 0
- The oxidation number of a monoatomic ion is the same as the charge on the ion
- Hydrogen in compounds has an oxidation number of +1, except in metal hydrides (or less electronegative elements) where it is -1
- Oxygen has an oxidation number of -2, except in H2O2, where it is -1
- For polyatomic ions (contains more than one ion), the sum of the oxidation numbers of the atoms equals the charge on the ion
- The sum of the oxidation of the atoms in a molecule
- The oxidation number of a group 1 element is +1
- The oxidation number of a group 2 element is +2
The reductant is the reactant that…
loses electrons and whose oxidation number increases
What do reductants include?
Metals - when metal atoms react, they lose electrons and are oxidised to form metal ions
What is the oxidation half equation, colour change and oxidation numbers for hydrogen?
H2(g) → 2H+(aq) + 2e-
colourless → colourless
0 +1
What is the oxidation half equation, colour change and oxidation numbers for zinc?
Zn(s) → Zn2+(aq) + 2e-
grey → colourless
0 +2
What is the oxidation half equation, colour change and oxidation numbers for magnesium?
Mg(s) → Mg2+(aq) + 2e-
grey → colourless
0 +2
What is the oxidation half equation, colour change and oxidation numbers for copper?
Cu(s) → Cu2+(aq) + 2e-
pink → (usually) blue
0 +2
What is the oxidation half equation, colour change and oxidation numbers for iron?
Fe(s) → Fe2+(aq) + 2e-
grey → pale green
0 +2
What is the oxidation half equation, colour change and oxidation numbers for iron (II)?
Fe2+(aq) → Fe3+(aq) + 2e-
pale green → yellow-orange
+2 +3
What is the oxidation half equation, colour change and oxidation numbers for bromide ions?
2Br-(aq) → Br2(aq) + 2e-
colourless → orange
-1 0
What is the oxidation half equation, colour change and oxidation numbers for iodide ions?
2I-(aq) → I2(aq) + 2e-
colourless solution → yellow-brown(aq) or black(s)
-1 0
What is the oxidation half equation, colour change and oxidation numbers for sulfite ions?
SO3^2-(aq) + H2O(l) → SO4^22-(aq) + 2H+(aq) + 2e-
colourless → colourless
+4 +6
What is the oxidation half equation, colour change and oxidation numbers for thiosulfate ions?
2S2O3^2-(aq) → S4O6^2-(aq) + 2e-
colourless → colourless
+2 +2.5
What is the oxidation half equation, colour change and oxidation numbers for hydrogen peroxide?
H2O2(l) → O2(g) + 2H+(aq) + 2e-
colourless → colourless
-1 0
What is oxidation half equation and colour change for hydrogen sulfide?
H2S(g) → S(s) + 2H+(aq) + 2e-
colourless → yellow
-2 0
The oxidant is the species that…
gains electrons and has a decrease in oxidation number
What condition are oxidants more effective in and how is it shown?
Acidic conditions and it is shown by “/H+(aq)”
What is the reduction half equation, colour change, oxidation number and condition for permanganate?
MnO4-(aq) + 8H+(aq) + 5e- → Mn2+(aq) + 4H2O(l)
purple → colourless
+7 +2
acidic
MnO4-(aq) + 4H+(aq) + 3e- → MnO2(s) + 2H2O(l)
purple → brown
+7 +4
neutral
MnO4-(aq) + e- → MnO4^2-(aq)
purple → green
+7 +6
basic
What is the reduction half equation, colour change, oxidation number and condition for manganese dioxide?
MnO2(s) + 4H+(aq) + 2e- → Mn2+(aq) + 2H2O(l)
brown → colourless
+4 +2
acidic
What is the reduction half equation, colour change, oxidation number and condition for dichromate?
Cr2O7^2-(aq) + 14H+(aq) + 6e- → 2Cr3+(aq) + 7H2O(l)
orange → green
+6 +3
acidic
What is the reduction half equation, colour change, oxidation number and condition for hydrogen peroxide?
H2O2(l) + 2H+(aq) + 2e- → 2H2O(l)
colourless → colourless
-1 -2
acidic
What is the reduction half equation, colour change and oxidation number for chlorine?
Cl2(g) + 2e- → 2Cl-(aq)
pale green → colourless
0 -1
What is the reduction half equation, colour change and oxidation number for iodine?
I2(aq) + 2e- → 2!-(aq)
yellow-brown(aq) or black-purple(s) → colourless(aq)
0 -1
What is the reduction half equation, colour change, oxidation number and condition for nitric acid?
2NO3-(aq) + 4H+(aq) + 2e- → 2NO2(g) + 2H2O(l)
colourless → brown gas
+5 +4
concentrated
What is the reduction half equation, colour change and oxidation number for iron (III) ions?
Fe3+(aq) + e- → Fe2+(aq)
yellow-orange → pale green
+3 +2
What is the reduction half equation, colour change and oxidation number for copper (II) ions?
Cu2+(aq) + e- → Cu+(aq)
(usually) blue → usually forms a white solid, red as Cu2O(s)
+2 +1
What are the steps for writing and balancing equations?
- Omit any spectator ions
- Separate them into two half equations (if given a full equation) or write the two half equations (if not given)
- Balance the atoms that aren’t O or H (do one half equation at a time)
- Balance the oxygen atoms by adding water to the appropriate side
- Balance the hydrogen ions by adding H+ ions to the appropriate side
- Balance the charges by adding electrons to the appropriate side (pay attention to coefficients)
- Check that one half equation is oxidation (e on right) and the other is reductions (e on left)
- Multiply the half equations, if necessary, so they both have the same number of electrons
- Cancel out the electrons and any other possible particles (can cancel on one side and subtract on the other)
- Add the two half equations
- Check that there is the same number of each atom and the same total charge in the reactants and products
Will a more or less reactive element undergo oxidation or reduction?
More reactive elements undergo oxidation and less reactive elements undergo reduction
