reactions in aqueous solution chapter 4 – part 2
TRANSCRIPT
Reactions in Aqueous Solution
Chapter 4 – Part 2
Question
What makes things work?
Why do substances do what they do?
Precipitation Reactions
Insoluble Solid Formation From the Mixing of Two
Solutions
Precipitation Reactions When one mixes two
solutions containing ions that form compounds that are insoluble, a precipitate is formed.
Why do they do that?
Solubility Rules for Common Ionic CompoundsIn water at 250C
Soluble Compounds ExceptionsCompounds 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 Exceptions
CO32-, PO4
3-, CrO42-, S2- Compounds containing
alkali metal ions and NH4+
OH- Compounds containing alkali metal ions and Ba2+
4.2
Molecular Equation
The molecular equation lists the reactants and products in their molecular form.
AgNO3 (aq) + KCl (aq) AgCl (s) + KNO3
(aq)
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)
Writing Net Ionic Equations
1. Write a balanced molecular equation.
2. Dissociate all strong electrolytes.
3. Cross out anything that remains unchanged from the left side to the right side of the equation.
4. Write the net ionic equation with the species that remain.
Precipitation Reactions
molecular equation
ionic equation
net ionic equation
____________ are spectator ions
Pb(NO3)2 (aq) + 2NaI (aq) PbI2 (s) + 2NaNO3 (aq)
precipitate
4.2
Gravimetric Analysis
4.6
1. Dissolve unknown substance in water
2. React unknown with known substance to form a precipitate
3. Filter and dry precipitate
4. Weigh precipitate
5. Use chemical formula and mass of precipitate to determine amount of unknown ion
Oxidation Reduction
Electron Transfer Reactions
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?
Displacement Reactions In displacement
reactions, ions oxidize or reduce an element.
The ions, then, are reduced or oxidized.
Displacement Reactions
In this reaction, silver ions oxidize copper metal.
Cu (s) + 2 Ag+ (aq) Cu2+ (aq) + 2 Ag (s)
Displacement Reactions
The reverse reaction, however, does not occur.
Cu2+ (aq) + 2 Ag (s) Cu (s) + 2 Ag+ (aq) x
Activity Series
Oxidation-Reduction Reactions(electron transfer reactions)
2Mg (s) + O2 (g) 2MgO (s)
Oxidation half-reaction (lose e-)
Reduction half-reaction (gain e-)
4.4
Zn (s) + CuSO4 (aq) ZnSO4 (aq) + Cu (s)
___ is oxidized
____ is reduced
___ is the reducing agent
___ is the oxidizing agent
4.4
Agents
4.4
Copper wire reacts with silver nitrate to form silver metal.What is the oxidizing agent in the reaction?
___ is reduced ___ is the oxidizing agent
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.
Types of Oxidation-Reduction Reactions
Combination ReactionA + B C
S + O2 SO2
Decomposition Reaction
2KClO3 2KCl + 3O2
C A + B
4.4
Displacement Reaction
A + BC AC + B
Sr + 2H2O Sr(OH)2 + H2
TiCl4 + 2Mg Ti + 2MgCl2
Cl2 + 2KBr 2KCl + Br2
Types of Oxidation-Reduction Reactions
4.4
Disproportionation Reaction
Cl2 + 2OH- ClO- + Cl- + H2O
Element is simultaneously oxidized and reduced.
Types of Oxidation-Reduction Reactions
4.4
Ca2+ + CO32- CaCO3
NH3 + H+ NH4+
Zn + 2HCl ZnCl2 + H2
Ca + F2 CaF2
4.4
Classify the Following Reactions
Oxidation Reduction
Balancing Equations That Cannot be Balanced by
Inspection
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 10/09/2006 11 AM