Copyright©2004 by houghton Mifflin Company. All rights reserved. Introductory Chemistry: A Foundation FIFTH EDITION by Steven S. Zumdahl University of Illinois Copyright©2004 by houghton Mifflin Company. All rights reserved. 1

Reactions in Aqueous Solutions Unit 2 Section 3 1

Overview In Chapter 7, goals for students are to: 1. Learn about some of the factors that cause reactions to occur. 2. Learn to identify the solid that forms in a precipitation reaction. 3. Learn to describe reactions in solution by writing molecular, complete, ionic, and net ionic equations. 4. Learn the key characteristics of reactions between strong acids and strong bases. 5. Learn the general characteristics of reactions between metals and nonmetals. 6. Understand electron transfer as a driving force for a chemical reaction. 7. Learn various classification schemes for reactions. 8. Consider additional classes of chemical reactions.

Predicting Whether a Reaction Will Occur Forces that drive a reaction formation of a solid (precipitate) formation of water transfer of electrons formation of a gas when chemicals (dissolved in water) are mixed and one of these 4 things can occur, the reaction will generally happen 2

What happens when an ionic compound dissolves in water? Ba(NO3)2 (aq) means barium nitrate has been dissolved in water Note: barium nitrate contains Ba2+ ions and NO3- ions When a solid containing ions is dissolved in water, the ions separate and move around NO3- NO3- Ba2+ NO3- NO3- Ba2+

Dissociation ionic compounds metal + nonmetal (Type I & II) metal + polyatomic anion polyatomic cation + anion Acids and Bases when ionic compounds dissolve in water the anions and cations are separated from each other; this is called dissociation we know that ionic compounds dissociate when they dissolve in water because the solution conducts electricity 4

Figure 7. 2: Electrical conductivity of aqueous solutions Figure 7.2: Electrical conductivity of aqueous solutions. (a) Pure water does not conduct an electric current. (b) When an ionic compound is dissolved in water, current flows and the lamp lights.

Dissociation Cu(SO4)(aq) = Cu+2(aq) + SO42-(aq) potassium chloride dissociates in water into potassium cations and chloride anions KCl(aq) = K+ (aq) + Cl- (aq) copper(II) sulfate dissociates in water into copper(II) cations and sulfate anions Cu(SO4)(aq) = Cu+2(aq) + SO42-(aq) K+ Cl- K Cl Cu+2 SO42- Cu SO4 5

K2(SO4)(aq) = 2 K+ (aq) + SO42-(aq) Dissociation potassium sulfate dissociates in water into potassium cations and sulfate anions K2(SO4)(aq) = 2 K+ (aq) + SO42-(aq) K+ SO42- K SO4 6

Precipitation Reactions in all precipitation reactions, the ions of one substance are exchanged with the ions of another substance when their aqueous solutions are mixed At least one of the products formed is insoluble in water KI(aq) + AgNO3(aq)  KNO3(aq) + AgIs K+ I- Ag+ NO3- Ag I 3

Predicting the Formation of a Precipitate How can you predict the formation of a precipitate in a double-replacement reaction? The mixing of two solutions can sometimes result in the formation of an insoluble salt called a precipitate. - We use solubility rules to determine which product is the precipitate Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Process for Predicting the Products of a Precipitation Reaction Determine what ions each aqueous reactant has Exchange Ions (+) ion from one reactant with (-) ion from other Balance Charges of combined ions to get formula of each product Balance the Equation count atoms Determine Solubility of Each Product in Water solubility rules if product is insoluble or slightly soluble, it will precipitate 7

Solubility Rules for Ionic Compounds Interpret Data Solubility Rules for Ionic Compounds Compounds Solubility Exceptions Salts of alkali metals and ammonia Soluble Some lithium compounds Nitrate salts and chlorate salts Few exceptions Sulfate salts Compounds of Pb, Ag, Hg, Ba, Sr, and Ca Chloride salts Compounds of Ag and some compounds of Hg and Pb Carbonates, phosphates, chromates, sulfides, and hydroxides Most are insoluble Compounds of the alkali metals and of ammonia Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Describing Reactions in Aqueous Solutions AIM: Learn to describe reactions in solution by writing molecular, complete, ionic, and net ionic equations.

Molecular Equations KNO3(aq) + AgCl(s) KCl(aq) + AgNO3(aq)  Describing Reactions in Aqueous Solutions Molecular Equations An equation showing the reactants and products in undissociated form Identify as solid (s), gas (g), liquid (l) or dissolved (aq) KCl(aq) + AgNO3(aq)  KNO3(aq) + AgCl(s)

Describing Reactions in Aqueous Solutions Ionic Equations An equation that shows all dissolved substances as ions (except for weak electrolytes and nonelectrolytes) K+(aq) + Cl-(aq) + Ag+ (aq) + NO3- (aq) K+ (aq) + NO3- (aq) + AgCl(s)

Cl- (aq) + Ag+ (aq) AgCl(s) Net Ionic Equations ions that are both reactants and products are called spectator ions K+ (aq) + Cl- (aq) + Ag+(aq) + NO3- (aq) K+ (aq) + NO3- (aq) + AgCl(s) an ionic equation in which the spectator ions are dropped is called a net ionic equation Cl- (aq) + Ag+ (aq) AgCl(s) 10

Describing Reactions in Solution Precipitation 1.Write the molecular equation, ionic equation, and net ionic equation for the reaction below. Identify spectator ions. Rubidium hydroxide (aq) reacts with calcium chloride (aq) to produce 

Describing Reactions in Solution Precipitation 1. Molecular equation (reactants and products as compounds) 2RbOH(aq) + CaCl2(aq)  Ca(OH)2(s) + 2RbCl(aq) 2. Complete ionic equation (all strong electrolytes shown as ions) 2Rb+(aq) + 2OH- (aq) + Ca+(aq) + 2Cl-(aq)  Ca(OH)2 (s) + 2Rb+(aq) + 2Cl-(aq)

Describing Reactions in Solution (continued) 3. Net ionic equation (show only components that actually react) Ca+(aq) + 2OH(aq)  Ca(OH)2 (s) Rb+ and Cl are “spectator” ions.

Predicting the Formation of a Precipitate Will a precipitate form when aqueous solutions of Na2CO3(aq) and Ba(NO3)2(aq) are mixed? Na2CO3(aq) + Ba(NO3)2 (aq) → Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 22

Molecular equation, complete ionic equation and net ionic equation

Molecular equation, complete ionic equation and net ionic equation

Write the Molecular, Complete Ionic, and Net ionic equations 1. Predict the products formed when aqueous solution of aluminum nitrate is mixed with sodium hydroxide solution. 2. Predict the products formed when a lead(II) nitrate solution is mixed with a sodium iodide solution

Problem 1 Predict the precipitate formed when aqueous solution of aluminum nitrate is mixed with sodium hydroxide solution.

Answer for Problem 1

Answer for Problem 1 Net Ionic Equation

Problem 2 Predict the precipitate formed when a lead(II) nitrate solution is mixed with a sodium iodide solution

Answer for Problem 2

Problem 2 Write the molecular equation, the complete ionic equation, and the net ionic equation when a lead(II) nitrate solution is mixed with a sodium iodide solution.

Answer for Problem 2 The molecular equation is The complete ionic equation is

Answer for Problem 2 The net ionic equation is

Strong Electrolytes Any compound that dissolves (dissociates) in water produces separated ions, the substance is called a strong electrolyte. - Examples: KCl, CuSO4 electrolytes are substances whose aqueous solution is a conductor of electricity in strong electrolytes, virtually all the molecules are dissociated into ions 11

Weak Electrolytes and Nonelectrolytes in nonelectrolytes, none of the molecules are dissociated into ions in weak electrolytes, a small percentage of the molecules are dissociated into ions 11

Video https://www.youtube.com/watch?v=3ulzo5VzLwY

Acids

Bases

Reactions that Form Water: Acids + Bases Acids all contain H+ cations and an anion Bases all contain OH- anions and a cation when acids dissociate in water they release H+ ions and their anions when bases dissociate in water they release OH- ions and their cations 12

https://prezi.com/z_o845wma1aw/acids-and-bases/ https://www.youtube.com/watch?v=WnPrtYUKke8

Strong acids and strong bases They are called strong acids. They are called strong bases.

Important Points about Strong Acids and Strong Bases Six strong acids HCl, HBr, HI, HNO3, H2SO4, HClO3 A strong acid is a substance that completely dissociates (ionizes) in water. (Each molecule breaks up into an H+ ion plus an anion. Strong bases metal hydroxides NaOH and KOH

Important Points about Strong Acids and Strong Bases In the reaction of a strong acid and a strong base, one product is always water and the other is always an ionic compound called a salt, which remains dissolved in the water. This salt can be obtained as a solid by evaporating the water.

acid + base salt + water Acid-Base Reactions in the reaction of an acid with a base, the H+ from the acid combines with the OH- from the base to make water the cation from the base combines with the anion from the acid to make the salt acid + base salt + water H2SO4(aq) + Ca(OH)2(aq)  CaSO4(aq) + 2 H2O(l) the net ionic equation for an Acid-Base reaction is always H+ (aq) + OH- (aq)  H2O(l) 13

Example of acid-base reaction NaOH + HCl 

End of Chapter 7