Precipitation Precipitation ReactionsReactions

Chapter 4 part IIIChapter 4 part III

What are the 6 types What are the 6 types of reactions ?of reactions ? SynthesisSynthesis DecompositionDecomposition CombustionCombustion Single replacementSingle replacement Double replacementDouble replacement Acid Base reactionAcid Base reaction

Solution reactionsSolution reactions

Precipitation reactions: a Precipitation reactions: a subset of replacement subset of replacement reactionsreactions

Acid Base reactionsAcid Base reactions Oxidation reduction Oxidation reduction

reactions: another subset of reactions: another subset of replacement reactionsreplacement reactions

Precipitation Rxns: 2 Precipitation Rxns: 2 solutions mix, and a solid solutions mix, and a solid is formedis formed

Precipitation ReactionsPrecipitation Reactions

When a solid containing ions When a solid containing ions dissolves in water, the ions dissolves in water, the ions separate.separate.

XY (s) XY (s) X+ (aq) + Y- (aq) X+ (aq) + Y- (aq) These ions move around These ions move around

independently in solution.independently in solution.

Formation of Formation of PrecipitatesPrecipitates When products form the solid When products form the solid

must have a zero net charge. It must have a zero net charge. It must contain both anions and must contain both anions and cations.cations.

Most ionic materials contain only Most ionic materials contain only two types of ions, cations and two types of ions, cations and anions.anions.

But in these double replacement But in these double replacement reactions which, how does one reactions which, how does one identify the solid? Demo?identify the solid? Demo?

Solubility Rules Solubility Rules (Thanks to (Thanks to

Professor Kenneth W. Busch)Professor Kenneth W. Busch)

1. Salts containing Group I elements are 1. Salts containing Group I elements are soluble (Li+, Na+, K+, Cs+, Rb+). Exceptions soluble (Li+, Na+, K+, Cs+, Rb+). Exceptions to this rule are rare. Salts containing the to this rule are rare. Salts containing the ammonium ion (NH4+) are also soluble. ammonium ion (NH4+) are also soluble. 2. Salts containing nitrate ion (NO3-) are 2. Salts containing nitrate ion (NO3-) are generally soluble. generally soluble. 3. Salts containing Cl -, Br -, I - are generally 3. Salts containing Cl -, Br -, I - are generally soluble. Important exceptions to this rule are soluble. Important exceptions to this rule are halide salts of Ag+, Pb2+, and (Hg2)2+. Thus, halide salts of Ag+, Pb2+, and (Hg2)2+. Thus, AgCl, PbBr2, and Hg2Cl2 are all insoluble. AgCl, PbBr2, and Hg2Cl2 are all insoluble. 4. Most silver salts are insoluble. AgNO3 and 4. Most silver salts are insoluble. AgNO3 and Ag(C2H3O2) are common soluble salts of Ag(C2H3O2) are common soluble salts of silver; virtually anything else is insoluble. silver; virtually anything else is insoluble. 5. Most sulfate salts are soluble. Important 5. Most sulfate salts are soluble. Important exceptions to this rule include BaSO4, PbSO4, exceptions to this rule include BaSO4, PbSO4, Ag2SO4, and CaSO4. Ag2SO4, and CaSO4.

Solubility continued:Solubility continued: 6. Most hydroxide salts are only slightly soluble. 6. Most hydroxide salts are only slightly soluble.

Hydroxide salts of Group I elements are soluble. Hydroxide salts of Group I elements are soluble. Hydroxide salts of Group II elements (Ca, Sr, and Hydroxide salts of Group II elements (Ca, Sr, and Ba) are slightly soluble. Hydroxide salts of Ba) are slightly soluble. Hydroxide salts of transition metals and Al3+ are insoluble. Thus, transition metals and Al3+ are insoluble. Thus, Fe(OH)3, Al(OH)3, Co(OH)2 are not soluble. Fe(OH)3, Al(OH)3, Co(OH)2 are not soluble. 7. Most sulfides of transition metals are highly 7. Most sulfides of transition metals are highly insoluble. Thus, CdS, FeS, ZnS, Ag2S are all insoluble. Thus, CdS, FeS, ZnS, Ag2S are all insoluble. Arsenic, antimony, bismuth, and lead insoluble. Arsenic, antimony, bismuth, and lead sulfides are also insoluble. sulfides are also insoluble. 8. Carbonates are frequently insoluble. Group II 8. Carbonates are frequently insoluble. Group II carbonates (Ca, Sr, and Ba) are insoluble. Some carbonates (Ca, Sr, and Ba) are insoluble. Some other insoluble carbonates include FeCO3 and other insoluble carbonates include FeCO3 and PbCO3. PbCO3. 9. Chromates are frequently insoluble. Examples: 9. Chromates are frequently insoluble. Examples: PbCrO4, BaCrO4 PbCrO4, BaCrO4 10. Phosphates are frequently insoluble. Examples: 10. Phosphates are frequently insoluble. Examples: Ca3(PO4)2, Ag2PO4 Ca3(PO4)2, Ag2PO4 11. Fluorides are frequently insoluble. Examples: 11. Fluorides are frequently insoluble. Examples: BaF2, MgF2 PbF2. BaF2, MgF2 PbF2.

The Good Guys & Bad The Good Guys & Bad GuysGuys

Three types of Three types of equationsequations Molecular equations: Molecular equations: Gives the over-all reaction Gives the over-all reaction

stoichiometry, but not stoichiometry, but not necessarily the actual forms necessarily the actual forms of the reactants and the of the reactants and the products.products.

HCl HCl (aq)(aq) + NaOH + NaOH (aq)(aq) H H22O O (l)(l) + NaCl + NaCl (aq)(aq)

Complete Ionic Complete Ionic EquationEquation

Represents as ions all Represents as ions all reactants & products that reactants & products that are strong electrolytes.are strong electrolytes.

HH++ (aq) + Cl (aq) + Cl-- (aq) + Na (aq) + Na++ (aq) + OH (aq) + OH-- (aq) (aq)

HH22O (l) + NaO (l) + Na++ (aq) + Cl (aq) + Cl-- (aq) (aq)

Net Ionic ReactionNet Ionic Reaction

This includes only those This includes only those solution components solution components undergoing a change. undergoing a change.

Spectator ions are not Spectator ions are not included.included.

HH++ (aq) + OH (aq) + OH-- (aq) (aq) H H22O (l)O (l)