1. Objectives
To learn more about some of the results of chemical reactions
To learn to predict the solid that forms in a precipitation reaction
To learn to write molecular, complete ionic, and net ionic equations

2. A. Common Results of a Reaction
Four common events accompany chemical reactions. These often occur when a reaction happens
Formation of a solid
Formation of water
Formation of a gas
Transfer of electrons
Can you give examples of each of these?

3. B. Precipitation Reactions
What Happens When an Ionic Compound Dissolves in Water?
H2O
NaCl (s)
NaCl (aq)
But what does NaCl (aq) mean?
Na+ and Cl- ions in water ?
NaCl molecules in water ?
Na and Cl atoms in water?

4. B. Precipitation Reactions
What Happens When an Ionic Compound Dissolves in
Water?
The ions separate and move around independently – a strong electrolyte

5. B. A Reaction in Which a Solid Forms
A reaction in which a solid is formed from a solution is called a precipitation reaction
Solid = precipitate = insoluble
When positive and negative ions form a precipitate the net charge of the precipitate is zero
Pb(NO3)2 (aq) + 2NaI (aq)
PbI2 (s) + 2NaNO3 (aq)

6. Stalactites in Yosemite
Ca(HCO3)2(aq)
→ CaCO3(s) +
H2O(l) + CO2(aq)

8. B. Precipitation Reactions
What Happens When Two Ionic Compounds Dissolve in
Water?
K2CrO4(aq) + Ba(NO3)2(aq)  Products

9. B. Precipitation Reactions
How to Decide What Products Form
Determine the possible products from the ions in the reactants.
In our example
K2CrO4(aq) + Ba(NO3)2(aq)  Products
The possible ion combinations are

10. What are the potential products in the reactions between the following aqueous solutions? – Write balanced equations for each
NaOH + CaCl2
CuBr2 + (NH4)2CO3
K2SO4 + Fe(NO3)3

11. B. Precipitation Reactions
How Would We Decide What Product Has Formed?
What is most likely to be the yellow solid formed in the following reaction?
K2CrO4(aq) + Ba(NO3)2(aq)
The possible product combinations are KNO3 and BaCrO4
KNO white solid
BaCrO yellow solid

12. B. Precipitation Reactions – Solubility Rules

13. B. Precipitation Reactions
Using Solubility Rules
Predicting Precipitates
Soluble solid
Insoluble solid
(Slightly soluble solid)
Why are some compounds soluble and others not?

14. Solubility Rules – Are These Compounds Soluble or Insoluble?
Barium Nitrate
Potassium Carbonate
Sodium Sulfate
Copper (II) Hydroxide
Mercury (I) Chloride
Ammonium Phosphate
Chromium (III) Sulfide
Lead (II) Sulfate

15. B. Precipitation Reactions
Let’s try some predictions: WOC P271 Q10

16. C. Describing Precipitation Reactions in Aqueous Solutions
Three types of equations:
Molecular (formula) equation 
complete formulas of all reactants and products
Complete ionic equation 
all strong electrolytes are shown as ions
Net ionic equation 
only those components of the solution that undergo a change
Spectator ion (those that remain unchanged) 
not shown in the net ionic equation

17. C. Describing Precipitation Reactions in Aqueous Solutions
Molecular Equation
Pb(NO3)2 (aq) + 2NaI (aq)
PbI2 (s) + 2NaNO3 (aq)
Complete Ionic Equation
Pb2+(aq) + 2NO3-(aq) + 2Na+(aq) + 2I-(aq)
PbI2(s) + 2Na+(aq) + 2NO3-(aq)

18. C. Describing Precipitation Reactions in Aqueous Solutions
Net Ionic Equation
Pb2+(aq) + 2I-(aq) PbI2(s)
What are the spectator ions in this reaction?
A solution of sodium chloride in water reacts with aqueous silver nitrate to give a precipitate of silver chloride – write down the three equations that describe this reaction and identify the spectator ions
(P272 Q14 – all three equations and identify spectators)