Transcript Oxidation-Reduction Rns

Oxidation-Reduction Rns
Ch.20 – 21
(p.630-686)
Oxidation states (or Numbers)
Assigning Oxidation states (numbers) to
individual elements in a chemical rn helps us
understand the ________ __ _______ during
the rn.
They can be assigned to elements whether they
are in an _____ compound or a _______
compound.
For Ionic Compounds:
The oxidation state of any element in a binary
ionic compound, is simply its ______.
For e.g.
NaCl consists of Na+ and ClNa+ has a charge of
but an oxidation state of
(note the difference)
Cl- has a charge of
but an oxidation state of
(note the difference)
E.g.’s for class to do
1.) MgCl2
2.) Al2O3
For Tertiary Ionic Compounds:
Tertiary Ionic compounds have __ or more elements
and contain __________ Ions.
e.g. Na2CO3 ; MgSO4 ; H3PO4 …
Assigning Oxidation states involves 3 steps.
1.) The 1st element retains its ________ _______
(number)
2.) The 3rd element (usually ______) retains its
________ ______ (number)
3.) The 2nd (middle) element is a ______ number that
“___________” (=0) the whole compound.
For e.g.
Na2CO3
1.) Na+ each have an oxidation # of
2.) O2- each have an oxidation # of
Sub Total:
3.) C must have an oxidation # to neutralise
Total:
In class examples:
Determine the Oxidation #’s of each of the elements:
1.) MgSO4
2.) H3PO4
3.) Na2S2O3
For Covalent molecules
For now, we shall deal with only Binary covalent molecules
who are sharing electrons.
e.g. …
Identify the ____ ElectroNegative (EN) element and “pretend”
that it has a ________ charge.
It is usually the ____ element in the molecule.
Identify the ____ EN element and “pretend” that it has a
________ charge.
It is usually the _____ element in the molecule.
Assign the Oxidation states based on their pretend charges.
For example:
CO2
O is more EN and its pretend charge is
and so it has an oxidation state of
with a total of
Therefore C, the least EN element,
must have an oxidation state of
because the molecule is neutral.
Example 2:
CH4
H is the least EN and its pretend charge is
and so it has an oxidation state of
with a total of
Therefore C, the more EN element, must
have an oxidation state of
because the molecule is neutral.
In class examples:
Determine the Oxidation #’s of each of the elements:
1.) H2O
2.) C2H6
3.) N2O5
Oxidation States for PolyAtomic Ions:
Previously, the compounds & molecules have been _______, and
therefore the oxidation states add up to __.
This time, the oxidation states add up to the ______.
E.g.
CO32O=
=
Total must =
therefore C must
=
In class e.g.’s:
Determine the Oxidation #’s of each of the elements:
1.) SO422.) PO433.) NH4+
Summary of the Rules:
1.) Elements by themselves have an Oxidation state of __.
e.g.
2.) Elements that have a charge, have an Oxidation state equal
to the ______.
e.g.
3.) Oxygen normally has an Oxidation state of __, except when it is
a Peroxide (O22-) it has a value of __
4.) Hydrogen normally has an Oxidation state of __, except
when combined with metals, it has a value of __
H2O H=
CaH2 H=
5.) For Neutral compounds, the sum of the Oxidation states
equals __
For Polyatomic Ions, the sum of the Oxidation states equals the
______.
Redox reactions involve the ________ of electrons from
the ________ agent to the _________ agent.
Oxidation: an ________ in oxidation number, but
a ____ of electrons.
Reduction: a ________ in oxidation number, but
a ____ of electrons.
The electron transfer occurs when the reactants collide.
The solns contain chemical energy and during these rns,
the energy is released as ____.
Therefore, the temperature of the soln will ________.
Redox Reactions
E.g. Mg(s) + HCl(aq) → H2(g) + MgCl2(aq)
Oxidised:
Reduced:
Reducing Agent:
Oxidising Agent:
E.g. CH4(g) + O2(g) → CO2(g) + H2O(g)
Oxidised:
Reduced:
Reducing Agent:
Oxidising Agent:
E.g. CaBr2(aq) + Na2O(aq) → CaO(s) + NaBr(aq)
i.e.
not all reactions are Redox Rns.