Precipitation+Reactions

General Information:
A **precipitation reaction** is a reaction between two ionic compounds to form two new compounds. A **precipitate** (abbreviated ppt) is a solid that will form in the bottom of a reaction vessel after a reaction has occurred if one of the compounds is insoluble. The reaction that occurs is a double replacement (double displacement) reaction. When this reaction happens, there __//cannot//__ be more than one precipitate.

In a precipitate reaction, the acid will give off H+ ions when dissolved in water. The base will give off OH- ions when dissolved in water.

Double Replacement reactions occur in the form AB + CD à AD + CB   where A and C are cations and B and D are anions.


 * Make sure to indicate whether each substance is aqueous (aq), solid (s), gas (g), or liquid (l).** An arrow pointing downwards may also be used to indicate a precipitate (solid).

Precipitation Reactions can be written in three forms: (see below for examples)
 * ====**Molecular form ** (shows molecules)====
 * ====**Complete ionic ** (shows all ions with only the precipitate as a molecule)====
 * ====**Net Ionic** (all spectator ions removed; includes only those which the precipitate includes)====

Solubility:

 * ======When something is considered **soluble**, that means that the attraction between the polar water molecules and also the attraction between ions is stronger than the attraction between the two ions. If this is the case, a __precipitate will not form__ and the ions will remain in solution.======
 * ======When something is considered **insoluble**, that means that the attraction between the two ions is stronger than the reaction between the polar water molecules and the two ions separately. If this is the case, a __precipitate will form__.======
 * ======A solubility chart should be used to determine solubility. Here is an example of a solubility chart. Many charts display the same information in different ways. This chart displays ions that are insoluble as having "low solubility". http://www.saskschools.ca/curr_content/chem30_05/appendix/tables_charts/sol_table.pdf======

Predicting Products for Precipitation Reactions:

 * 1) ======Take the first cation and pair it with the opposite anion.======
 * 2) ======Take the second cation and pair it with the opposite anion.======
 * 3) ======Look at a solubility chart to determine whether or not a precipitate will form and if so, what it is.======
 * 4) ======Balance the equation.======

**Examples**: Each of the following is a "textbook" reaction and molecular forms would not usually be written unless the species exist largely undissociated in solution (unless otherwise noted).
===**1. Reaction between calcium nitrate and carbonic acid: ( **species exist largely undissociated in solution**) ** === __//**Molecular form: **//__ //**__Net Ionic: __**  // As seen above, CaCO3 is the precipitate.
 * //__Complete ionic: __//**



2. Reaction between iron(III) chloride and phosphoric acid:
__//**Molecular form: **//__ //**__<span style="color: rgb(128,0,128);">Net Ionic: __**// As seen above, FePO4 is the precipitate.
 * //__<span style="color: rgb(0,0,255);">Complete ionic: __//**

<span style="color: rgb(0,128,128);">3. Reaction between potassium nitrate and sodium iodide:
__//**<span style="color: rgb(255,0,0);">Molecular form: **//__ //**__<span style="color: rgb(128,0,128);">Net Ionic: __**//<span style="color: rgb(0,0,0);"> None because **no precipitate forms** and nothing can be removed as spectators.
 * //__<span style="color: rgb(0,0,255);">Complete ionic: __//**

No precipitate forms and all species remain in aqueous solution due to all species being soluble according to a solubility chart.

<span style="color: rgb(0,128,128);">4. Reaction between sodium hydroxide and copper(II) sulfate:
See here in picture form: http://www.bbc.co.uk/schools/gcsebitesize/science/images/42_transition_metal.gif

__//**<span style="color: rgb(255,0,0);">Molecular form: **//__ //**__<span style="color: rgb(128,0,128);">Net Ionic: __**// As seen above, Cu(OH)2 is the precipitate
 * //__<span style="color: rgb(0,0,255);">Complete ionic: __//**

Precipitate Reactions in Action!
In the following video, sodium carbonate is added to each substance unless otherwise noted. media type="youtube" key="RjBjwQF276A" height="344" width="425"

**Final Note: Remember to use solubility rules** to figure out whether or not a precipitate will form!
<span style="color: rgb(0,255,0); font-family: 'Arial Black',Gadget,sans-serif; background-color: rgb(0,0,128);">Places to Practice: http://www.wisc-online.com/objects/index_tj.asp?objID=GCH2904 http://www.mhhe.com/physsci/chemistry/animations/chang_7e_esp/crm3s2_3.swf

<span style="color: rgb(0,255,0); font-family: 'Arial Black',Gadget,sans-serif; background-color: rgb(0,0,128);">Works Cited: http://chemistry.twu.edu/tutorial/TypeChemRxSum.html http://hyperphysics.phy-astr.gsu.edu/Hbase/chemical/precip.html http://www.ausetute.com.au/ppteeqtn.html http://www.saskschools.ca/curr_content/chem30_05/4_solutions/solution3_4.htm __[]__ Brown, Theodore L., Eugene H. Lemay, Jr., Bruce E. Bursten, and Catherine J. Murphy. __Chemistry: The Central Science__. 10th ed. New Jersey: Pearson Education, Inc. 2006.