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 m...
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.
Metathesis Reactions
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.
There are only two types of Chemical Changes:
Now we will begin to learn another system for classifying reactions…
1. Reactions in which electrons are being transferred from atom(s) to atom(s). REDOX
…based on: • What electrons do in a chemical reaction. • How reactants are changed.
2. Reactions in which ions are being rearranged with no change in their oxidation states. METATHESIS
Metathesis Reactions
Reaction Types Metathesis Double Displacement
Neutralization
•
Redox Precipitation
Ion Exchange Ions are combined to form new compounds
Single Displacement
Combustion
Synthesis
Decomposit
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 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. 2. form predominantly unionized molecules like H2O(l) and CO2(g). Ion removal is the driving force of metathesis reactions.
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Metathesis Reactions
Precipitate Reactions
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.
Formation of a solid ionic precipitate from the combination of two ionic solutions. Must begin with two soluble reactants
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
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
Solubility guidelines predict the formation of a precipitate
Remember, there are three ways we write chemical equations:
1. Molecular Equations 2. Full Ionic Equations 3. Net Ionic Equations
Reactions that involve ions should always be written as net ionic equations.
Full Ionic Equations • Represents all reactants and products that are strong electrolytes as ions.
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Considerations When Writing Full Ionic Equations
2. Re-write the molecular equations from problem # 1 as full ionic equations.
• Weak electrolytes / weak acids and bases, are not dissociated • Solids, liquids and gases are not dissociated • Physical states are included
Considerations When Writing Net Ionic Equations
Net Ionic Equations • Includes only those solution components undergoing change • Spectator ions are not included.
• 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 equations.
Metathesis Reactions 2. Acid-Base (neutralization) Reactions – Formation of the nonelectrolyte H2O 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
Neutralization • Molecular equation
Ca(OH)2 (aq) + 2 HNO3(aq) → Ca(NO3 ) 2 ( aq) + 2 H 2O(l ) Total
Net
ionic equation
Neutralization • Molecular equation
HBr(aq) + KOH (aq) → KBr(aq) + H 2 O ( l ) Total
Net
ionic equation
ionic equation
Metathesis Reactions 3. Double Displacement reactions – Are reactions where two aqueous solutions result in the formation of nonelectrolyte compounds other than water.
ionic equation
What do you notice about neutralization reactions involving strong acids and bases?
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 equations.
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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!
