1. Reactions in Aqueous Solution
Chapter 4 – Part 2

2. Question
What makes things work?
Why do substances do what they do?

3. Precipitation Reactions
Insoluble Solid Formation From the Mixing of Two Solutions

4. Precipitation Reactions
When one mixes two solutions containing ions that form compounds that are insoluble, a precipitate is formed.
Why do they do that?

5. Solubility Rules for Common Ionic Compounds In water at 250C
Soluble Compounds
Exceptions
Compounds containing alkali metal ions and NH4+
None
NO3-, HCO3-, ClO3-
Cl-, Br-, I-
Halides of Ag+, Hg22+, Pb2+
SO42-
Sulfates of Ag+, Ca2+, Sr2+, Ba2+, Hg2+, Pb2+
Insoluble Compounds
CO32-, PO43-, CrO42-, S2-
OH-
Compounds containing alkali metal ions and Ba2+
4.2

6. AgNO3 (aq) + KCl (aq)  AgCl (s) + KNO3 (aq)
Molecular Equation
The molecular equation lists the reactants and products in their molecular form.
AgNO3 (aq) + KCl (aq)  AgCl (s) + KNO3 (aq)

7. Ionic Equation
In the ionic equation all strong electrolytes (strong acids, strong bases, and soluble ionic salts) are dissociated into their ions.
This more accurately reflects the species that are found in the reaction mixture.
Ag+ (aq) + NO3- (aq) + K+ (aq) + Cl- (aq) 
AgCl (s) + K+ (aq) + NO3- (aq)

8. Writing Net Ionic Equations
Write a balanced molecular equation.
Dissociate all strong electrolytes.
Cross out anything that remains unchanged from the left side to the right side of the equation.
Write the net ionic equation with the species that remain.

9. Precipitation Reactions
precipitate
Pb(NO3)2 (aq) + 2NaI (aq) PbI2 (s) + 2NaNO3 (aq)
molecular equation
ionic equation
net ionic equation
____________ are spectator ions
4.2

10. Gravimetric Analysis Dissolve unknown substance in water
React unknown with known substance to form a precipitate
Filter and dry precipitate
Weigh precipitate
Use chemical formula and mass of precipitate to determine amount of unknown ion
4.6

11. Electron Transfer Reactions
Oxidation Reduction
Electron Transfer Reactions

12. Oxidation-Reduction Reactions
If a substance gives up electrons, something must have collided with that substance and accepted the electrons.
Why do they do that?

13. Displacement Reactions
In displacement reactions, ions oxidize or reduce an element.
The ions, then, are reduced or oxidized.

14. Displacement Reactions
In this reaction,
silver ions oxidize
copper metal.
Cu (s) + 2 Ag+ (aq)  Cu2+ (aq) + 2 Ag (s)

15. Displacement Reactions
The reverse reaction,
however, does not
occur.
Cu2+ (aq) + 2 Ag (s)  Cu (s) + 2 Ag+ (aq) x

16. Activity Series

17. Oxidation-Reduction Reactions
(electron transfer reactions)
2Mg (s) + O2 (g) MgO (s)
Oxidation half-reaction (lose e-)
Reduction half-reaction (gain e-)
4.4

18. Zn (s) + CuSO4 (aq) ZnSO4 (aq) + Cu (s)
Agents
Zn (s) + CuSO4 (aq) ZnSO4 (aq) + Cu (s)
___ is oxidized
___ is the reducing agent
____ is reduced
___ is the oxidizing agent
4.4

19. Copper wire reacts with silver nitrate to form silver metal.
What is the oxidizing agent in the reaction?
___ is reduced
___ is the oxidizing agent
4.4

20. Oxidation Numbers
To determine if an oxidation-reduction reaction has occurred, we assign an oxidation number to each element in a neutral compound or charged entity.
Review the rules on calculating an oxidation number for atoms in a compound.

21. Types of Oxidation-Reduction Reactions
Combination Reaction
A + B C
S + O SO2
Decomposition Reaction
C A + B
2KClO KCl + 3O2
4.4

22. Types of Oxidation-Reduction Reactions
Displacement Reaction
A + BC AC + B
Sr + 2H2O Sr(OH)2 + H2
TiCl4 + 2Mg Ti + 2MgCl2
Cl2 + 2KBr KCl + Br2
4.4

23. Types of Oxidation-Reduction Reactions
Disproportionation Reaction
Element is simultaneously oxidized and reduced.
Cl2 + 2OH ClO- + Cl- + H2O
4.4

24. Ca2+ + CO32- CaCO3 NH3 + H+ NH4+ Zn + 2HCl ZnCl2 + H2 Ca + F2 CaF2
Classify the Following Reactions
Ca2+ + CO CaCO3
NH3 + H NH4+
Zn + 2HCl ZnCl2 + H2
Ca + F CaF2
4.4

25. Balancing Equations That Cannot be Balanced by Inspection
Oxidation Reduction
Balancing Equations That Cannot be Balanced by Inspection

26. Balancing Redox Equations
Break into Half Reactions
Balance Half Reactions
Balance all but H,O
Balance O with water
Balance H with H+
Balance charge with e-
Add Half Reactions Together
Practice Due 10/09/ AM