1. Precipitation Reactions
Definitions
When two solutions are mixed and a solid forms
Precipitate = solid that forms from a precipitation reaction
K2CrO4(aq) + Ba(NO3)2(aq)2K+(aq) + CrO42-(aq) + Ba2+(aq) +2NO3-(aq)
K2CrO4 and Ba(NO3)2 are both soluble (all dissolve in water)
A yellow precipitate forms when these solutions are mixed
K2CrO4(aq) + Ba(NO3)2(aq) > BaCrO4(s) + 2KNO3(aq)
AgNO3(aq) + KCl(aq) > AgCl(s) + KNO3(aq) + =
Precipitate Spectator Ions

2. B. Solubility Rules
Examples: predict what will happen when you mix:
KNO3(aq) + BaCl2(aq) >
Na2SO4(aq) + Pb(NO3)2(aq) >
3KOH(aq) + Fe(NO3)2(aq) >

3. Reactions that give off gases
Sometimes the product of a reaction is not a solid, but a gas
We can still observe that something happened: bubbles form
Compound that reacts with acid
Equation for Formation of the gas
Gas produced
Sulfides
2H+ + S2-  H2S
H2S
Carbonates
2H+ + CO32-  H2CO3  H2O + CO2
CO2
Bicarbonates
H+ + HCO3-  H2CO3  H2O + CO2
Sulfites
2H+ + SO32-  H2O + SO2
SO2
Bisulfites
H+ + HSO3-  H2O + SO2
Cyanides
H+ + CN-  HCN
HCN
Compound that reacts with base
Ammonium salts
NH OH-  NH3 + H2O
NH3

4. D. Describing Reactions in Solution
Molecular Equation shows what compounds the ions came from
Does not give clear picture of what happens in solution
K2CrO4(aq) + Ba(NO3)2(aq) > BaCrO4(s) + 2KNO3(aq)
Complete Ionic Equation represents the form of the ions in solution
All strong electrolytes are represented as their ions
2K+(aq) + CrO42-(aq) + Ba2+(aq) +2NO3-(aq) ----> BaCrO4(s) + 2K+(aq) + 2NO3-(aq)
Net Ionic Equation shows only the ions participating in the reaction
The K+ and NO3- ions occur on both sides of the complete ionic eqn.
These spectator ions can be cancelled out of each side (algebra)
Ba2+(aq) CrO42-(aq) > BaCrO4(s)
Example
3KOH(aq) + Fe(NO3)3(aq) > Fe(OH)3(s) + 3KNO3(aq)
b. 3K+(aq) + 3OH-(aq) + Fe3+(aq) + 3NO3-(aq) ----> Fe(OH)3(s) + 3K+(aq) + 3NO3-(aq)
c. Fe3+(aq) + 3OH-(aq) > Fe(OH)3(s)

5. Example of What We Will Do Today (with different compounds)
1. Given MgCl2, HCl, Pb(NO3)2, K2CO3, and NaOH
D or E must be HCl and K2CO3 or vice versa
D must be HCl: bubbles, 1 precip, 2 N.R.
E must be K2CO3
MgCl2 reacts with HCl and K2CO3 to give N.R
And white precip. Only A does this. A = MgCl2
5. MgCl2 has 3 white precipitates
6. C = Pb(NO3)2 has 4 white precip.
7. B = NaOH gives two precip.’s and 2 NR
White ppt
MgCl2
HCl
Pb(NO3)2
K2CO3
N.O.R. X
White ppt
Bubbles
NaOH

6. Incident: NaOH Clothing Damage Incident: Acid Splash on Latex Gloves