Precipitate Formation When two clear solutions are mixed a blue precipitate is produced.

Purpose To observe a double displacement reaction which occurs in solution To represent the chemical reaction using an ionic equation

Demonstration The clear, colorless calcium chloride solution when mixed with the cobalt chloride solution formed a new solution containing calcium ions chloride ions cobalt(II)hydroxide precipitate The cobalt(II) hydroxide was blue and appeared as a blue suspension in the solution which sunk to the bottom of the beaker

Concepts 1. Solution Chemistry 2. Ionic Equations 3. Solubility

1. Solution Chemistry Each solution contains a different salt Salts are made of ions Pink solution CoCl2(s) Co2+(aq) + 2Cl-(aq) Clear solution Ca(OH)2(s) Ca2+(aq) + 2(OH-)(aq) H2O H2O

2. Ionic Equations The chemical equation for the mixed solutions is Co2+(aq) + 2Cl-(aq) + 2Ca2+(aq) + 2(OH-)(aq) 2Ca2+(aq) + 2Cl-(aq) + Co(OH)2(s) The net ionic equation is Co2+(aq) + 2(OH-)(aq) Co(OH)2(s)

3. Solubility When the cobalt ion and the hydroxide ions are present in the same solution, they bond tightly to form a new compound which is insoluble Co(OH)2(s) On the other hand, when the calcium and chloride ions are present, the salt that could form is soluble, thus exists as individual ions in solution CaCl2(s) Ca2+(aq) + Cl-(aq) H2O

Conclusions If both calcium chloride and cobalt chloride were soluble salts, no reaction would have occurred Since at least one of the possible products was insoluble, the reaction occurred as shown by the color change and formation of the blue precipitate The chemical reaction in this demonstration was a double replacement reaction

Comments This reaction is not a redox reaction since the ionic species do not change oxidation number The hydroxides of many metals are insoluble and form precipitates