Metathesis Reactions. Metathesis Reactions

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1 Make sure as we go through the material for the third unit exam that you read the text and study the concepts presented in both the text and lecture materials. The homework for this unit will only focus on skill development. It is up to you to learn the concepts and vocabulary from the text. One of the biggest mistakes students make in this unit is not studying the material from the text and trying to link it to lecture. We have already seen that reactions can be classified based on how atoms rearrange. Now we will begin to learn another system for classifying reactions based on: What electrons do in a chemical reaction. How reactants are changed. There are only two types of Chemical Changes: 1. Reactions in which electrons are being transferred from atom(s) to atom(s). REDOX. Reactions in which ions are being rearranged with no change in their oxidation states. METATHESIS Metathesis Reaction Types Redox Double Neutralization Precipitation Single Combustion Synthesis Decomposit Displacement Displacement Ion Exchange Ions are combined to form new compounds Electron Transfer Electrons are lost from one atom, or group of atoms, and gained by another atom, or group of atoms, resulting in new atomic interactions forming new compounds Handout Metathesis Reactions Metathesis reactions Metathesis reactions occur when two ionic aqueous solutions are mixed and the ions switch partners. AX + BY AY + BX Metathesis reactions remove ions from solution in two ways: 1. form an insoluble solid.. form predominantly unionized molecules like H O (l) and CO (g). Ion removal is the driving force of metathesis reactions. 1

2 1. Precipitation reactions are metathesis reactions in which an insoluble compound is formed from two aqueous solutions. The solid precipitates out of the solution much like rain or snow precipitates out of the air. Precipitate Reactions Formation of a solid ionic precipitate from the combination of two ionic solutions. Must begin with two soluble reactants Solubility guidelines predict the formation of a precipitate 1. Write the Molecular equation for each of the following solution pairs, using the solubility rules for predicting the precipitate formed. Silver nitrate and tin (IV) chloride Potassium iodide and lead (II) nitrate Magnesium sulfate and barium hydroxide Remember, there are three ways we write chemical equations: 1. Molecular Equations. Full Ionic Equations 3. Net Ionic Equations Reactions that involve ions should always be written as net ionic Molecular Equations Gives overall reaction stoichiometry, but NOT necessarily the actual forms of reactants & products involved in the reaction Should include the correct physical states Full Ionic Equations Represents all reactants and products that are strong electrolytes as ions.

3 Considerations When Writing Full Ionic Equations Weak electrolytes / weak acids and bases, are not dissociated. Re-write the molecular equations from problem # 1 as full ionic Solids, liquids and gases are not dissociated Physical states are included Net Ionic Equations Includes only those solution components undergoing change Spectator ions are not included. Considerations When Writing Net Ionic Equations If the substance is not soluble, or only partially soluble in water, write the molecular formula. If the substance forms a soluble salt, strong base or strong acid, write the ionic form. 3. Re-write the molecular equations from problem # 1 as net ionic Precipitation Reactions 3CaCl + Na 3 PO 4 6 NaCl + Ca 3 PO ( 4 ) (s) Total ionic reaction Net ionic reaction 3

4 . Acid-Base (neutralization) Reactions Formation of the nonelectrolyte H O acid + base salt + water A salt is another name for an ionic compound formed from the cation of a base and an anion from an acid HBr + Neutralization KOH KBr Total ionic equation Net ionic equation + H O ( l) Ca(OH) Neutralization + HNO Ca(NO 3 3) + HO( l) Total ionic equation Metathesis Reactions 3. Double Displacement reactions Are reactions where two aqueous solutions result in the formation of nonelectrolyte compounds other than water. Net ionic equation What do you notice about neutralization reactions involving strong acids and bases? Double Displacement Reactions HCl + Na SO NaCl + H O + SO 3 Total ionic reaction Net ionic reaction ( l) ( g) You should see why it is important to memorize: Solubility Rules Strong Acids/Bases Polyatomic ions On my exams you will be responsible for writing molecular equations as well as on every exam, there is a section where you will write net ionic 4

5 Summary Question Barium sulfate is a commonly used imaging agent for gastrointestinal X-rays. This compound can be prepared by some of the simple reactions described in this chapter. Write a balanced molecular reaction and a net ionic reaction for the production of barium sulfate. You can choose any aqueous starting materials that will form barium sulfate! 5