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Unit 3: Presentation C Precipitation Reactions
AP Chemistry Slide 3 / 20 Types of Chemical Reactions Seashells are created by the precipitation reaction below. Ca2+(aq) + CO32-(aq) --> CaCO3(s) Slide 4 / 20 Types of Reactions
Chemical reactions are classified by what process is occurring by means of the reaction.
Type What is occurring Example Precipitation formation of solid from mixing of two aqueous solution
Co2+(aq) + 2OH-(aq) --> Co(OH)2(s)
Acid/Base exchange of H+ ions NH4+(aq) + OH-(aq) --> NH3(aq) + H2O(l) Redox exchange of electrons
Mg(s) + Zn2+(aq) --> Mg2+(aq) + Zn(s)
*Note: There are a few reactions that do not neatly fit into one
- f these categories. They will be dealt with later.
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Precipitation Reactions
In order to predict the products of a precipitation reaction, we must know which ions tend to be soluble in water and which ones tend not to be soluble. Always soluble Soluble unless with Ag+, Hg+,
- r Pb2+
Soluble unless with Ag+, Hg+, Pb2+, Ca2+, Sr2+, Ba2+ Insoluble unless paired with ion that always dissolves acetate nitrate nitrite ammonium alkali metal ions chlorate bicarbonate chloride bromide iodide sulfate hydroxide phosphate carbonate sulfide flouride sulfite chromate
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When writing a precipitation reaction, a few simple steps must be followed. Example: If aqueous solutions of potassium hydroxide and barium nitrate are mixed... Picture what ions are present K+(aq) + OH-(aq) + Ba2+(aq) + NO3-(aq) Decide which ions will form a ppt. and show the reaction of these ions only in the formation of the ppt. product K+(aq) + OH-(aq) + Ba2+(aq) + NO3-(aq) 2OH-(aq) + Ba2+(aq) --> Ba(OH)2(s) Note: Ions not involved in the reaction are known as spectator ions. The spectator ions here are K+(aq) and NO3-(aq).