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