Common Rxn Types
• Double Displacement Precipitation Rxns
• Acid-Base Rxns
• Oxidation-Reduction Rxns (Redox)
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Combustion
Single Displacement
Photosynthesis
Rusting
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Oxidation-Reduction Rxns or Redox
• Oxidation-Reduction Rxns are rxns where electrons
are transferred between the reactants.
• Since electrons are electrical energy, there is a
transfer of electrical energy.
• Many common examples are combustion, oxidation,
and single displacement rxns.
– AgNO3(aq) + Na(s)  Ag(s) + NaNO3(aq)
– HNO3(aq) + Na(s)  H2(g) + NaNO3(aq)
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Redox Rxns
• What do all these rxns have in common?
• One reactant gains electrons while another reactant
loses electrons.
• The first redox rxns extensively studied were
oxidation rxns.
• In oxidation rxns, the element or compound reacting
with oxygen gas transferred electrons to oxygen.
• So they said that they were oxidized.
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Vocabulary of Redox Rxns
• Oxidation: the process of losing electrons. The
compound or element which loses electrons is
oxidized. The compound or element which is oxidized
is the reducing agent or the reductant, as it gives
electrons to the other reactant.
• Reduction: the process of gaining electrons. The
compound or element which gains electrons is
reduced. The compound or element which is reduced
is the oxidizing agent or the oxidant, as it takes or
accepts electrons from the other reactant.
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Vocabulary of Redox Rxns
• Oxidation Number or Oxidation State: A number
which is assigned to an atom which is a “pretend”
ionic charge. It is the charge the atom would have if it
were ionic. We assign oxidation numbers with a set of
rules.
• Memorization Hint: Use OIL RIG to remember
which is which. It stands for: Oxidation Is Losing;
Reduction Is Gaining.
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Goals
1. Learn how to assign oxidation states to all the atoms in a
substance.
2. Using oxidation numbers, determine whether the rxn is a
redox rxn.
3. If it is a redox rxn, determine which reactant is being
oxidized and which is being reduced.
4. For single displacement redox rxns, learn the activity
series to predict whether a rxn will occur and what the
products are.
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Assigning Oxidation States
•
Here are the rules for assigning oxidation states in
order of precedence:
1. Atoms in their elemental states have an oxidation number
of 0.
2. Monatomic ions have an oxidation state equal to their
charge.
3. In ionic compounds with a monatomic cation, the cation’s
oxidation state equals its ionic charge in the compound.
4. Hydrogen is +1 when it is combined with nonmetals, and it
is -1 when it is combined with metals.
5. Fluorine has an oxidation number of -1 in compounds.
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Assigning Oxidation States
•
Here are the rules for assigning oxidation states in
order of precedence:
6. Oxygen usually has an oxidation number of -2. It has an
oxidation number of -1 in peroxides, and is -1/2 in
superoxides (these are obtained by the cation charge).
7. Halogens usually have an oxidation number of -1, except
when combined with oxygen or fluorine.
8. In molecular compounds or in polyatomic ions, the more
electronegative element (one closer to F or to the right of
the Periodic Table) is assigned an oxidation number equal
to its normal ionic charge.
9. The sum of all of the individual oxidation numbers in a
substance must equal the overall charge of the substance.
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Assigning Oxidation States
• Assign oxidation numbers to all the atoms in
the following:
S8
C2H4
H2SO4
H2SO3
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Determining Whether A Rxn is Redox
• Now you get to use the oxidation numbers!
• Once you assign oxidation numbers to all the
atoms in a rxn, you look for changes.
• If the oxidation number of an atom changes
from a reactant to a product, then it is a redox
rxn.
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Determining Whether A Rxn is Redox
• Ex: Is the following rxn redox?
Al(s) + HCl(aq)  AlCl3(aq) + H2(g)
1) Assign oxidation numbers to all atoms.
2) Are the oxidation numbers of any atoms changing?
If yes, it is redox.
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What’s Being Reduced and Oxidized
• Look at the following rxn again.
Al(s) + HCl(aq)  AlCl3(aq) + H2(g)
• You know that this is a redox as Al is going
from 0 in Al(s) to 3+ in AlCl3; and because H is
changing from +1 in HCl to 0 in H2.
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What’s Being Reduced and Oxidized
• So if the oxidation state of Al is changing from
(from reactant to product) 0 to 3+, is it gaining
or losing electrons? So is it being oxidized or
reduced?
• If the oxidation state of H is changing from 1 to
0, is it gaining or losing electrons? So is it
being oxidized or reduced?
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What’s Being Reduced and Oxidized
• How do we state this? We say that Al is being
oxidized, while HCl or H in HCl is being
reduced. Or we say that Al is the reductant,
while HCl is the oxidant. Notice that I need say
nothing about the products.
• The above highlights a very important fact
about redox rxns: if something is being
reduced, something else MUST be oxidized!
You can’t have one without the other.
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What’s Being Reduced and Oxidized
• Determine what substance is being oxidized
and what’s being reduced in the following:
CH4 + 2O2  2H2O + CO2
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Activity Series & Single Displacement Rxns
• Single displacement rxns occur when a metallic element
reacts with a cation (or the cation of an ionic
compound) or it reacts with acid.
• M + NX  N + MX
• M + HX  H2 + MX
• Cr + CuCl2  Cu + CrCl3
• Sn + HCl  SnCl2 + H2
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Activity Series & Single Displacement Rxns
• The product is another element and another
ionic compound.
• So the cation swaps places with the element.
• What are the predicted products: silver metal
is mixed with cupric nitrate sln?
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Activity Series & Single Displacement Rxns
• But how do you know whether a single
displacement rxn occurs or not? After all, not
all metals are equally reactive.
• You know for example, that Group 1 is the
most reactive metal group.
• So is it likely that silver metal would react with
sodium nitrate to form silver nitrate and
sodium metal?
• To predict whether a single displacement rxn
actually occurs, we use a Metal Activity Series.
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Metal Activity Series
• Li, Rb, K, Ba, Ca, Na (in order of decreasing
reactivity)
• These metals react with oxygen to produce
oxides; acids to produce hydrogen gas and a
salt; and cold water to produce hydrogen gas
and an oxide or a hydroxide salt.
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Metal Activity Series
• Mg, Al, Mn, Zn, Cr, Fe (in order of decreasing
reactivity and less than those before)
• These metals react with oxygen to produce
oxides; acids to produce hydrogen gas and a
salt; and steam to produce hydrogen gas and an
oxide or a hydroxide salt.
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Metal Activity Series
• Co, Ni, Sn, Pb (in order of decreasing reactivity
and less than those before)
• These metals react with oxygen to produce
oxides; and acids to produce hydrogen gas and
a salt.
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Metal Activity Series
• H2, Cu, Ag (in order of decreasing reactivity
and less than those before)
• These “metals” react with oxygen to produce
oxides.
• Remember hydrogen isn’t a metal, but it is a
dividing line between metals that react with
acids and metals that don’t!
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Metal Activity Series
• Hg, Pt, Au (in order of decreasing reactivity
and less than those before)
• Mostly unreactive (please note that the position
of Ag and Hg is sometimes reversed).
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Metal Activity Series
• Classically, the activity series tells you what
metal will react in a single displacement rxn:
A + BC  B + AC
• If A is the more reactive metal than B, or A is
less stable than B, or A is higher on the Table
than B, then the rxn will occur.
• If A is a less reactive metal than B, or A is
lower on the Table than B, then the rxn will not
occur.
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Metal Activity Series
• What this really says is that the more stable
metal (the less reactive metal) is produced.
• So a more reactive metal will react with an
aqueous ionic salt sln of a less reactive metal,
forming the less reactive metal and an ionic salt
sln of the more active metal.
• Metals which are above hydrogen gas on the
Table also react with strong acids to produce
hydrogen gas and an ionic salt sln.
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Metal Activity Series
• For the following, predict whether the rxn will
occur and if it does, write the balanced
equation:
• Nickel shot is added to 6M hydrochloric acid.
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Halogen Activity Series
• There is a halogen series just as there is a metal
activity series.
• Another type of single displacement rxn is
when a halogen element reacts with another
halogen ion (or an ionic compound with a
halogen anion).
F2 + NaCl  Cl2 + NaF
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Halogen Activity Series
• Fluorine is the most active halogen, while
iodine is the least active halogen (size factor
which affects bond strength).
• Problem: Will the following rxn occur? If so,
write the balanced equation.
• Fluorine gas is mixed with sodium bromide.
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