chapter 20 oxidation-reduction reactions anything in black letters = write it in your notes...
TRANSCRIPT
Chapter 20Chapter 20
Oxidation-Reduction ReactionsOxidation-Reduction Reactions
Anything in black letters = write it in your notes (‘knowts’)
20.1 – The Meaning of Oxidation and Reduction20.1 – The Meaning of Oxidation and Reduction
Combining with oxygen
ReductionLoss of oxygen
Oxidation cannot occur without reduction.
Oxidation
Original definitions, still useful…
Combining with oxygen
ReductionLoss of oxygen
Oxidation
CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)
4Fe(s) + 3O2(g) → 2Fe2O3(s)
2Fe2O3(s) + 3C(s) → 4Fe(s) + 3CO2(g)
Circle the substance that is being oxidized
Loss of electrons
ReductionGain of electrons
Oxidation
Modern definitions, more useful…
Helpful acronym…
‘LEO the lion says GER’
gerLoss of Electrons is Oxidation
Gain of Electrons is Reduction
Mg(s) + S(s) MgS(s)heat
OxidationLoss of electrons
ReductionGain of electrons
Mg is oxidized because it lost 2 e-
A substance can be oxidized without reacting with oxygen.
Oxidizing Agent – causes another substance to be oxidized.
Reducing Agent – causes another substance to be reduced.
2C + O2 2COReducing Agent
Oxidizing Agent
Carbon is oxidized, oxygen is reduced.
The oxidizing agent will always be reduced
2AgNO3(aq) + Cu(s) → Cu(NO3)2(aq) + 2Ag(s)
Circle the oxidizing agent
20.2 – Oxidation Numbers20.2 – Oxidation Numbers
This section is really a review…This section is really a review…
Oxidation Number – charge on an ion.
Elements & compounds have an oxidation # of zero.
Mg + Cl2 MgCl2
-1+20 0
Mg0 Mg+2 + 2e-
Cl20 + 2e- 2Cl-1
Loss of e- = oxidation
Gain of e- = reduction
Rules for Assigning Oxidation Numbers
1. The oxidation number of a monatomic ion is equal in magnitude and sign to its ionic charge. For example, the oxidation number of the bromide ion (Br1–) is –1; that of the Fe3+ ion is +3.
2. The oxidation number of hydrogen in a compound is +1, except in metal hydrides, such as NaH, where it is –1.
3. The oxidation number of oxygen in a compound is –2, except in peroxides, such as H2O2, where it is –1, and in compounds with the more electronegative fluorine, where it is positive.
4. The oxidation number of an atom in uncombined (elemental) form is 0. For example, the oxidation number of the potassium atoms in potassium metal (K) or of the nitrogen atoms in nitrogen gas (N2) is 0.
5. For any neutral compound, the sum of the oxidation numbers of the atoms in the compound must equal 0.
6. For a polyatomic ion, the sum of the oxidation numbers must equal the ionic charge of the ion.
These should make sense…don’t write them all down!These should make sense…don’t write them all down!
What is the oxidation number of each kind of atom in the following ions and compounds?
a. SO2
b. Na2SO4
c. CO32–
d. Cu2S
ASSIGNMENT:
Chapter 20 Worksheet #1
20.3 – Describing Redox Rxns20.3 – Describing Redox Rxns
Not covered…Not covered…