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Single replacement and Double replacement
Mr. Shields Regents Chemistry L11 L06
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Reaction TypesReaction Types
A+BCAB+CAX+BYAY+BX
Combustion
We’ve discussed Synthesis, Decomposition and Combustion.Let’s now look at Single and Double Replacement reactions.
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Single ReplacementSingle Replacement
In a single replacement reaction an UNCOMBINED Element replaces one of the elements in a compound.
A+BCAB+C
+
A + B---C B----A + C
A replaces C and C becomes the uncombined element
uncombined uncombined
+
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Single ReplacementSingle Replacement
Typically the compounds involved in single replacement Reactions are ionic and occur in solution. For example…
Cl2 + 2NaBr (aq) 2NaCl (aq) + Br2
+ +
Example:
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Single ReplacementSingle Replacement
The reaction of Chlorine to replace Bromine is an exampleOf a NON-METAL REPLACING A NON-METAL
Cl2 + 2NaBr (aq) 2NaCl (aq) + Br2
There are also single replacement reactions in which aMETAL REPLACES ANOTHER METAL.
2AgNO3 (aq) + Cu Cu(NO3)2 (aq) + 2Ag
-In single replacement reactions:- Metals will only replace metals- Non-metals will only replace non-metals
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Single ReplacementSingle Replacement
2AgNO3 (aq) + Cu (s) Cu(NO3)2 (aq) + 2Ag (s)
Let’s look at what’s happening in this reaction…
ClearAgNO3
sol’n &Solid CuWire
BlueCu(NO3)2
Sol’n &Solid Ag
The silver in this reaction “precipitates” out of the solution
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Single ReplacementSingle Replacement
In single replacement reactions:
- Metals replace metals
- Halogen Non-metals replace halogen non-metals
F2 Cl2 Br2 I2
K Al Fe Cu
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We saw Copper can replace Ag but there are otherMetals that will replace metals as well. For exampleZinc will replace Cu in ionic compounds.
Zn(s) + CuSO4(aq) ZnSO4(aq) + Cu (s)
Cu wire isIn an aqueousSolution of AgNO3
Zn & Cu
Cu & Ag
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Activity SeriesActivity Series
We know certain metals will replace other metalsAnd certain Non-metals will replace other non-metals.
But how can we determine which will replace which?
To make this determination you need to refer to
TABLE J
in your reference tables.
TABLE J IS KNOWN AS THE ACTIVITY SERIES
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In the activity series the element higher on the list willReplace from a compound any element lower on the list.
For example: Al (s) + Cr(NO3)3 (aq) Al(NO3)3 (aq) + Cr (s)
or 3Cl2 (g) + 2AlI3 (aq) 2AlCl3 (aq) + 3I2 (s)
More reactive
Less Reactive
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The activity series also lists Hydrogen with the metals. AnyMetal higher on the list than hydrogen will replace it fromEither water or acid.
2K + 2H20 2KOH + H2
Ni + 2HCl NiCl2 + H2
If the uncombined metal is below the combined metal(or hydrogen) it will not replace it from the compoundand the reaction will NOT OCCUR !!
Replacing hydrogen from water is more difficult than Replacing hydrogen from acids. But, those metals higher Up the activity series will react with water more easily.
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Try theseTry theseWill these reactions proceed as indicated?
1)3Mg + 2Fe(NO3)3 3Mg(NO3)2 + 2Fe
2)Pb + Co(NO3)2 Pb(NO3)2 + Co
3)Br2 + 2KCl 2KBr + CL2
4)2Au + 6HCl 2AuCl3 + 3H2
5) Zn + 2HNO3 Zn(NO3)2 + H2
Yes
No
No
No
Yes
Notice in all these reactions a new compound and a freeElement are formed
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Double Replacement ReactionsDouble Replacement Reactions
As with single replacement reactions Double replacementReactions take place with ionic compounds in solution.
In this case however, both reactants are compounds.
For example …
H replaces Na
Na replaces H
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Double Replacement ReactionsDouble Replacement ReactionsThese reactions occur in solution because the ions of thecompounds must be able to move freely from one place toanother
H+ + NO3- + 2Na+ + CO3
-2 2H+ + CO3-2 + Na+ + NO3
-
This equation is known as a COMPLETE IONIC EQUATION
Since these compounds are all in sol’n we can write theequation a little differently showing all the ions present:
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Double Replacement ReactionsDouble Replacement ReactionsMaybe you’re wondering “if this reaction can occur as Indicated in solution why can’t the reverse reactionHappen just as easily?”
2H+ + CO3-2 + Na+ + NO3
- H+ + NO3- + 2Na+ + CO3
-
2
In other words …
Well it can! So in order for these reactions to proceed Forward to completion something else must occur
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Double Replacement
“A molecule forms”
The criteria necessary to drive double replacement reactionsForward to completion will be one of the following:
We’ll discuss thisOne in a later unit
Reaction Start Reaction Complete
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1- Precipitate forms1- Precipitate formsSome compounds are INSOLUABLE in water. Therefore,In double replacement reactions the IONS of these Insoluble compounds are noLonger free and therefore canNot react with other free ions
For example:
Ba(NO3)2 (aq) + CuSO4 (aq) Cu(NO3)2 (aq) + BaSO4 (s)
These insoluble compounds that areFormed are known as PRECIPITATES
A common precipitate
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Another example of a common precipitate that forms in This kind of reactions is AgCl
A white precipitate
Ions in the Complete Ionic Equation that are not involvedIn forcing the double replacement reaction to completionAre known as SPECTATOR IONS. For example, the aboveEquation can be rewritten as a NET IONIC EQUATION …
Ag+ + Cl- AgCl (s)
Double Replacement
The only ionsInvolved in Driving the reaction to completion
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Gas EvolutionGas EvolutionThe other type of double replacement reaction that goes To completion is one in which a gas is evolved.
For example …
H2CO3 H20 + CO2 (g)
Carbonic acid is theAcid that gives soda itsfizz
Once the gas is evolved, the ions from which its generatedAre no longer available. The rxn is driven to completion
Decomposes
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Molecule formationMolecule formation
The last process we’ll discuss that drives doublereplacement reactions to completion are reactions thatLead to the formation of molecules (i.e. covalently bonded Compounds like water)
Molecules can not ionize and thus once formed they areNo longer available for replacement reactions.
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Molecule formationMolecule formation
The most common example of molecule formation is ACID-BASE neutralization. In this type of double replacementReaction WATER is the molecular compound that’s formed
For example:HCl + KOH KCl + H2O
Complete ionic equation:H+ + Cl- + K+ + OH- K+ + Cl- + H2O
Net Ionic equation:H+ + OH- H2O (the general equation for acid-base neutralizations)
Acid Base A Salt Water
A “Molecule”
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Try theseTry theseName the reaction type:
CaCO3 CaO + CO2
CH4 + O2 CO2 + H20
Mg + ZnCl2 MgCl2 + Zn
MgSO4 (aq) + Ba(NO3)2 (aq) BaSO4 (s) + Mg(NO3)2 (aq)
Mg + H2SO4 MgSO4 + H2 (g)
HCL + Ca(OH)2 CaCl2 + H20
Decomp
Combustion
Single Rep.
Double Rep.Single Rep.
Double Rep.
CO2 + H2O H2CO3 Synthesis
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