1. 4.3 Single Displacement and Double Displacement Reactions
SCH3U
Ms. Munir

2. Single Displacement Reactions
In a single displacement reaction, one element in a compound is displaced (or replaced) by another element.
There are 2 different types of SD reactions.
One type involves a metal replacing a metal cation in a compound. A + BC → AC + B
Zn(s) + Fe(NO3)2(aq) → Zn(NO3)2(aq) + Fe(s)
The second type of SD reaction involves a non-metal (usually a halogen) replacing an anion in a compound. DE + F → DF + E
Cl2(g) + CaBr2(aq) → CaCl2(aq) + Br2(g)

3. Single Displacement Reactions and the Metal Activity Series
Most single displacement reactions involve one metal displacing another metal from a compound.
Mg(s) + ZnCl2(aq) → MgCl2(aq) + Zn(s)
Treat hydrogen as a metal.
Treat acids, such as HCl, as ionic compounds of the form H+Cl−.
Treat water as ionic, with the formula H+(OH−).

4. Metal Activity Series

5. Predicting SD Products
If the metal displacing a cation is higher in the series, reaction will take place.
Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)
If the metal displacing a cation is lower in the series, no reaction will take place.
Ag(s) + CaCl2(aq) → N.R.

6. Single Displacement Reactions Involving Halogens
The activity series for halogens directly mirrors the position of halogens in the periodic table.
F>Cl>Br>I
Cl2(g) + 2KBr(aq) → 2KCl(aq) + Br2(l)
I2(aq) + CaBr2(aq) → NR

7. Double Displacement Reactions
A double displacement reaction involves the exchange of cations between two ionic compounds, usually in aqueous (water) solution. A DD reaction is also known as a double replacement reaction.
AB + CD → CB + AD
NaCl(aq) + AgNO3(aq) → AgCl(s) + NaNO3(aq)

8. Continued… DD reaction takes place when: a solid (precipitate) forms
a gas is produced
some DD reactions also form a molecular compound, such as water. It is hard to tell when water is formed, because often the reaction takes place in water.

9. Double Displacement Reactions that Form a Precipitate
A precipitate is a solid that separates from a solution as the result of a chemical reaction.
BaCl2(aq) + K2SO4(aq) → BaSO4(s) + 2KCl(aq)

10. Think about this… How do we determine the products?
Deconstruct and reconstruct the equation
Which of the products—if any—will precipitate out of solution?
Learn solubility chart [later in the course]

11. Double Displacement Reactions That Produce a Gas
The gas is formed when one of the products of the double displacement reaction decomposes to give water and a gas.
Na2CO3(aq) + 2HCl(aq) → 2NaCl(aq) + H2CO3(aq)
H2CO3(aq) → H2O(l) + CO2(g)
Na2CO3(aq) + 2HCl(aq) → 2NaCl(aq) + H2O(l) + CO2(g)

12. The Formation of Water in Neutralization
Neutralization reactions are a special type of DD reaction that produces water. Neutralization involves the reaction of an acid with a base to form water and an ionic compound (salt).
HNO3(aq) + NaOH(aq) → NaNO3(aq) + H2O(l)
P #1 – 6 McGrawHill
P 169 # 1 – 9 Nelson
P 177 #1 – 7 Nelson