Precipitation ReactionsSolubility

·When two solutions containing dissolved ions (eg. ionic compounds) are mixed, the ions will come into contact. Oppositely charged particles attract and sometimes the attraction is strong enough to form new compounds. Sometimes these compounds cannot dissolve in water and a solid forms.

The insoluble solid formed is called a precipitate. Reactions in which precipitates form are called precipitation reactions.

·How can the precipitate of a chemical reaction be determined?·The solubility rules!

Solubility Rules

·All compounds containing either the Na+, NH4

+, K+, or NO3

- ion will dissolve in water·Compounds containing the Cl-, Br- and I- ions are soluble (except when they contain Ag+, Pb2+ or Hg2+ ions)·Compounds containing the SO4

2- ions are soluble (except when they contain Ba2+, Pb2+ or Ca2+ ions)·Compounds containing CO3

2- and PO4

3- are insoluble (except when they contain Na+, NH4

+ or K+ ions)·Compounds containing OH- are insoluble (except when they contain Na+, NH4

+, or K+ ions)·Some compounds are slightly soluble; Ca(OH)2, PbCl2, PbBr2, CaSO4 and Ag2SO4

Precipitation Reactions·Reaction in which a solid is formed

--> Precipitate·Reaction Classification:

Double Displacement / Replacement

AB + CD --> AD + CB

ExampleKI(aq) + AgNO3(aq) --> KNO3 + AgIHow do we know which one is the precipitate?

Solubility rules (handout)Insoluble – forms a precipitate

Soluble – remains dissociated (does not form a precipitate)

KI(aq) + AgNO3(aq) --> KNO3(aq) + AgI(s)

Predicting the Precipitate Determine Solubility of Each Product

·Solubility rules (handout)·if product is insoluble or slightly soluble, it will precipitate

ExampleBa(NO3)2(aq) + CuSO4(aq) --> BaSO4 + Cu(NO3)2

Which product will be the precipitate???·Use your solubility rules handoutSO4

2- always soluble except with Ba2+

Therefore BaSO4

is insoluble --> Precipitate!

Ba(NO3)2(aq) + CuSO4(aq) --> BaSO4(s) + Cu(NO3)2(aq)

http://www.mhhe.com/physsci/chemistry/animations/chang_7e_esp/crm3s2_3.swf

IONS

Dissociation·“To break apart”·When an ionic solid dissolves in water, the ions separate and move independently

http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/molvie1.swf

Determine what ions each aqueous reactant has

EXAMPLES

NaCl(aq) + AgNO3(aq) --->

K2SO4(aq) + NaOH(aq) --->

CaCl2(aq) + Na2CO3(aq) --->

Cu(NO3)2(aq) + NaOH(aq) --->