Chemistry
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CW single replacement reactions content 032012.doc
Single Replacement Reactions
As you have found out from your overview of chemical reactions,
a single replacement reaction is one where an element reacts with
a compound (often in aqueous solution) and an element and a
compound are produced.
A single replacement reaction is the chemical equivalent of
"cutting in" at the chemical prom.
Continuing our theme of studying the behavior of ions in solution,
we will concentrate on single replacement reactions that occur in
aqueous solution. If a reaction occurs and the element is a metal,
then it will replace the metal in the compound. If a reaction
occurs, and the element is a halogen, then it will replace the halogen in the compound.
Zn(s) + Cu(NO3)2(aq) → Zn(NO3)2(aq) + Cu(s)
Cl2(aq) + 2NaI(aq) → 2NaCl(aq) + I2(aq)
Goals for your study of single replacement reactions:
1. Recognize a reaction as being single replacement.
2. Be able to predict if a reaction will occur or not (using the activity series).
3. Determine the formulas of the products (paying attention to oxidation numbers).
4. Determine if the compound that is formed is insoluble in water (solubility rules).
5. Balance the molecular equation.
6. Write a balanced net ionic equation.
And just like some couples refuse to let someone cut in, some
single replacement reactions simply don't occur. For instance,
zinc metal will react with copper ions in solution ...
Zn(s) + Cu(NO3)2(aq) → Zn(NO3)2(aq) + Cu(s)
… which means that zinc can "cut in", but copper metal won't
react with zinc ions at all.
Cu(s) + Zn(NO3)2(aq) → no reaction
Zinc nitrate doesn't allow copper to "cut in".
So just why do some single replacement reactions occur and
others do not?
Goal One -- Pick out the single replacement reactions:
1) F2 + NaBr → NaF + Br2
2) Ca(OH)2 + Al2(SO4)3 → CaSO4 + Al(OH)3
3) Mg + Fe2O3 → Fe + MgO
4) C2H4 + O2 → CO2 + H2O
5) PbSO4 → PbSO3 + O2
6) NH3 + I2 → N2I6 + H2
7) H2O + SO3 → H2SO4
8) H2SO4 + NH4OH → H2O + (NH4)2SO4
9) Na + H2O → NaOH + H2
10) H2 + I2 → HI
Did you find four reactions which
are single replacement? List the
numbers on the line below:
___________________________
Balance all of the reactions for
practice, and identify the type of
reaction for the remaining
reactions.
Do that on notebook paper.
Goal Two -- Predict if a single replacement reaction actually will occur.
Just like it is important to be able to determine if a
double replacement reaction actually occurs when two
compounds are mixed together by looking at the
solubility rules, we must determine if a reaction occurs in
a single replacement reaction. Will the element replace
an element in a compound?
To make that determination we use the activity series.
You can find the activity series in your NCDPI reference
tables on page 7. It is reprinted here for your
convenience.
Earlier, we mentioned the following two reactions. If a
piece of zinc is added to a solution of copper(II) nitrate
the zinc will dissolve to form zinc(II) ions (Zn2+). The
copper(II) ions (Cu2+) will come out of solution as
copper metal and deposit on the surface of the zinc.
Zn(s) + Cu(NO3)2(aq) → Zn(NO3)2(aq) + Cu(s)
If, instead, a piece of copper is added to a solution of
zinc ions in solution, nothing will happen. The copper
metal is not active enough to replace the zinc ions in
solution.
Cu(s) + Zn(NO3)2(aq) → no reaction
We can predict those results by looking at the position of
zinc and copper on the activity series. Zinc is well above
copper, which is close to the bottom of the table.
A metal will replace the ions below it, but not above
it, in the activity series.