Chapter Four TYPES OF CHEMICAL REACTIONS AND SOLUTION

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Chapter Four: TYPES OF CHEMICAL REACTIONS AND SOLUTION STOICHIOMETRY

Chapter Four: TYPES OF CHEMICAL REACTIONS AND SOLUTION STOICHIOMETRY

Water, the Common Solvent • One of the most important substances on earth •

Water, the Common Solvent • One of the most important substances on earth • Can dissolve many different substances • A polar molecule 4. 1 2 Copyright © Houghton Mifflin Company. All rights reserved.

Dissolution of a Solid in a Liquid 4. 1 3 Copyright © Houghton Mifflin

Dissolution of a Solid in a Liquid 4. 1 3 Copyright © Houghton Mifflin Company. All rights reserved.

Nature of Aqueous Solutions • Solute – substance being dissolved • Solvent – liquid

Nature of Aqueous Solutions • Solute – substance being dissolved • Solvent – liquid water • Electrolyte – substance that when dissolved in water produces a solution that can conduct electricity 4. 2 4 Copyright © Houghton Mifflin Company. All rights reserved.

Electrolytes • Strong Electrolytes – conduct current very efficiently (bulb shines brightly) • Weak

Electrolytes • Strong Electrolytes – conduct current very efficiently (bulb shines brightly) • Weak Electrolytes – conduct only a small current (bulb glows dimly) • Nonelectrolytes – no current flows (bulb remains unlit) 4. 2 5 Copyright © Houghton Mifflin Company. All rights reserved.

Electrolyte Behavior 4. 2 6 Copyright © Houghton Mifflin Company. All rights reserved.

Electrolyte Behavior 4. 2 6 Copyright © Houghton Mifflin Company. All rights reserved.

Chemical Reactions of Solutions • We must know: – Nature of the reaction –

Chemical Reactions of Solutions • We must know: – Nature of the reaction – Amounts of chemicals present in the solutions 4. 3 7 Copyright © Houghton Mifflin Company. All rights reserved.

Molarity • Molarity (M) = moles of solute per volume of solution in liters:

Molarity • Molarity (M) = moles of solute per volume of solution in liters: 4. 3 8 Copyright © Houghton Mifflin Company. All rights reserved.

Concept Check Which of the following solutions contains the greatest number of ions? a)

Concept Check Which of the following solutions contains the greatest number of ions? a) b) c) d) 400. 0 m. L of 0. 10 M Na. Cl. 300. 0 m. L of 0. 10 M Ca. Cl 2. 200. 0 m. L of 0. 10 M Fe. Cl 3. 800. 0 m. L of 0. 10 M sucrose. 4. 3 9 Copyright © Houghton Mifflin Company. All rights reserved.

Let’s Think About It • Draw molecular level pictures showing each solution. Think about

Let’s Think About It • Draw molecular level pictures showing each solution. Think about relative numbers of ions. • How many moles of each ion are in each solution? 4. 3 10 Copyright © Houghton Mifflin Company. All rights reserved.

Notice The solution with the greatest number of ions is not necessarily the one

Notice The solution with the greatest number of ions is not necessarily the one in which: – the volume of the solution is the largest. – the formula unit has the greatest number of ions. 4. 3 11 Copyright © Houghton Mifflin Company. All rights reserved.

Dilution • The process of adding water to a stock solution to achieve the

Dilution • The process of adding water to a stock solution to achieve the molarity desired for a particular solution. • Dilution with water does not alter the numbers of moles of solute present. • Moles of solute before dilution = moles of solute after dilution M 1 V 1 = M 2 V 2 4. 3 12 Copyright © Houghton Mifflin Company. All rights reserved.

Types of Chemical Reactions • Precipitation Reactions • Acid-Base Reactions • Oxidation-Reduction Reactions 4.

Types of Chemical Reactions • Precipitation Reactions • Acid-Base Reactions • Oxidation-Reduction Reactions 4. 4 13 Copyright © Houghton Mifflin Company. All rights reserved.

Precipitation Reaction • A double displacement reaction in which a solid forms and separates

Precipitation Reaction • A double displacement reaction in which a solid forms and separates from the solution. – When ionic compounds dissolve in water, the resulting solution contains the separated ions – Precipitate – the solid that forms 4. 5 14 Copyright © Houghton Mifflin Company. All rights reserved.

The Reaction of K 2 Cr. O 4(aq) and Ba(NO 3)2(aq) • Ba 2+(aq)

The Reaction of K 2 Cr. O 4(aq) and Ba(NO 3)2(aq) • Ba 2+(aq) + Cr. O 42–(aq) → Ba. Cr. O 4(s) solid Ba. Cr. O 4 formed 4. 5 15 Copyright © Houghton Mifflin Company. All rights reserved.

Precipitation of Silver Chloride 4. 5 16 Copyright © Houghton Mifflin Company. All rights

Precipitation of Silver Chloride 4. 5 16 Copyright © Houghton Mifflin Company. All rights reserved.

Precipitates • Soluble – solid dissolves in solution; (aq) is used in reaction •

Precipitates • Soluble – solid dissolves in solution; (aq) is used in reaction • Insoluble – solid does not dissolve in solution; (s) is used in reaction • Insoluble and slightly soluble are often used interchangeably 4. 5 17 Copyright © Houghton Mifflin Company. All rights reserved.

Simple Rules for Solubility 1. 2. 3. 4. 5. 6. Most nitrate (NO 3

Simple Rules for Solubility 1. 2. 3. 4. 5. 6. Most nitrate (NO 3 ) salts are soluble. Most alkali (group 1 A) salts and NH 4+ are soluble. Most Cl , Br , and I salts are soluble (except Ag+, Pb 2+, Hg 22+). Most sulfate salts are soluble (except Ba. SO 4, Pb. SO 4, Hg 2 SO 4, Ca. SO 4). Most OH salts are only slightly soluble (Na. OH, KOH are soluble, Ba(OH)2, Ca(OH)2 are marginally soluble). Most S 2 , CO 32 , Cr. O 42 , PO 43 salts are only slightly soluble. 4. 5 18 Copyright © Houghton Mifflin Company. All rights reserved.

Describing Reactions in Solution • Formula Equation (Molecular Equation) – Reactants and products as

Describing Reactions in Solution • Formula Equation (Molecular Equation) – Reactants and products as compounds Ag. NO 3(aq) + Na. Cl(aq) Ag. Cl(s) + Na. NO 3(aq) • Complete Ionic Equation – All strong electrolytes shown as ions Ag+(aq) + NO 3 (aq) + Na+(aq) + Cl (aq) Ag. Cl(s) + Na+(aq) + NO 3 (aq) 4. 6 19 Copyright © Houghton Mifflin Company. All rights reserved.

Describing Reactions in Solution • Net Ionic Equation – Show only components that actually

Describing Reactions in Solution • Net Ionic Equation – Show only components that actually react Ag+(aq) + Cl (aq) Ag. Cl(s) – Na+ and NO 3 are spectator ions 4. 6 20 Copyright © Houghton Mifflin Company. All rights reserved.

Concept Check You have two separate beakers with aqueous solutions, one with 4 “units”

Concept Check You have two separate beakers with aqueous solutions, one with 4 “units” of potassium sulfate and one with 3 “units” of barium nitrate. a) Draw molecular level diagrams of both solutions. 4. 6/4. 7 21 Copyright © Houghton Mifflin Company. All rights reserved.

Concept Check You have two separate beakers with aqueous solutions, one with 4 “units”

Concept Check You have two separate beakers with aqueous solutions, one with 4 “units” of potassium sulfate and one with 3 “units” of barium nitrate. b) Draw a molecular level diagram of the mixture of the two solutions before a reaction has taken place. 4. 6/4. 7 22 Copyright © Houghton Mifflin Company. All rights reserved.

Concept Check You have two separate beakers with aqueous solutions, one with 4 “units”

Concept Check You have two separate beakers with aqueous solutions, one with 4 “units” of potassium sulfate and one with 3 “units” of barium nitrate. c) Draw a molecular level diagram of the product and solution formed after the reaction has taken place. 4. 6/4. 7 23 Copyright © Houghton Mifflin Company. All rights reserved.

Solution Stoichiometry Problems • Identify the species present in the combined solution. • Write

Solution Stoichiometry Problems • Identify the species present in the combined solution. • Write the balanced net ionic equation. • Calculate the moles of reactants. • Determine limiting reactant. • Calculate the moles of product(s). • Convert to grams or other units. 4. 7 24 Copyright © Houghton Mifflin Company. All rights reserved.

Acid-Base Reactions (Brønsted-Lowry) • Acid – proton donor • Base – proton acceptor •

Acid-Base Reactions (Brønsted-Lowry) • Acid – proton donor • Base – proton acceptor • For a strong acid and base reaction: H+(aq) + OH–(aq) H 2 O(l) 4. 8 25 Copyright © Houghton Mifflin Company. All rights reserved.

Neutralization of a Strong Acid by a Strong Base 4. 8 26 Copyright ©

Neutralization of a Strong Acid by a Strong Base 4. 8 26 Copyright © Houghton Mifflin Company. All rights reserved.

Key Titration Terms • Titrant – solution of known concentration used in titration •

Key Titration Terms • Titrant – solution of known concentration used in titration • Analyte – substance being analyzed • Equivalence point – enough titrant added to react exactly with the analyte • Endpoint – the indicator changes color so you can tell the equivalence point has been reached 4. 8 27 Copyright © Houghton Mifflin Company. All rights reserved.

Performing Calculations for Acid-Base Reactions 1. 2. 3. 4. 5. 6. List initial species

Performing Calculations for Acid-Base Reactions 1. 2. 3. 4. 5. 6. List initial species and predict reaction. Write balanced net ionic reaction. Calculate moles of reactants. Determine limiting reactant. Calculate moles of required reactant or product. Convert to grams or volume, as required. 4. 8 28 Copyright © Houghton Mifflin Company. All rights reserved.

Oxidation-Reduction Reactions (Redox Reactions) • Reactions in which one or more electrons are transferred.

Oxidation-Reduction Reactions (Redox Reactions) • Reactions in which one or more electrons are transferred. 4. 9 29 Copyright © Houghton Mifflin Company. All rights reserved.

Reaction of Sodium and Chlorine 4. 9 30 Copyright © Houghton Mifflin Company. All

Reaction of Sodium and Chlorine 4. 9 30 Copyright © Houghton Mifflin Company. All rights reserved.

Rules for Assigning Oxidation States 1. 2. 3. 4. 5. 6. 7. Oxidation state

Rules for Assigning Oxidation States 1. 2. 3. 4. 5. 6. 7. Oxidation state of an atom in an element = 0 Oxidation state of monatomic element = charge Oxygen = 2 in covalent compounds (except in peroxides where it = 1) Hydrogen = +1 in covalent compounds Fluorine = 1 in compounds Sum of oxidation states = 0 in compounds Sum of oxidation states = charge of the ion 4. 9 31 Copyright © Houghton Mifflin Company. All rights reserved.

Exercise Find the oxidation states for each of the elements in each of the

Exercise Find the oxidation states for each of the elements in each of the following compounds: • • • K 2 Cr 2 O 7 CO 32 Mn. O 2 PCl 5 SF 4 4. 9 32 Copyright © Houghton Mifflin Company. All rights reserved.

Redox Characteristics • • Transfer of Electrons Transfer may occur to form ions Oxidation

Redox Characteristics • • Transfer of Electrons Transfer may occur to form ions Oxidation – increase in oxidation state (loss of electrons); reducing agent Reduction – decrease in oxidation state (gain of electrons); oxidizing agent 4. 9 33 Copyright © Houghton Mifflin Company. All rights reserved.

Concept Check Which of the following are oxidation-reduction reactions? Identify the oxidizing agent and

Concept Check Which of the following are oxidation-reduction reactions? Identify the oxidizing agent and the reducing agent. a) b) c) Zn(s) + 2 HCl(aq) Zn. Cl 2(aq) + H 2(g) Cr 2 O 72 -(aq) + 2 OH-(aq) 2 Cr. O 42 -(aq) + H 2 O(l) 2 Cu. Cl(aq) Cu. Cl 2(aq) + Cu(s) 4. 9 34 Copyright © Houghton Mifflin Company. All rights reserved.

Balancing Oxidation-Reduction Reactions • Cr 2 O 72 -(aq) + SO 32 -(aq) Cr

Balancing Oxidation-Reduction Reactions • Cr 2 O 72 -(aq) + SO 32 -(aq) Cr 3+(aq) + SO 42 -(aq) • How can we balance this equation? • First Steps: – Separate into half-reactions – Balance elements except H and O 4. 10 35 Copyright © Houghton Mifflin Company. All rights reserved.

Method of Half Reactions • Cr 2 O 72 -(aq) 2 Cr 3+(aq) •

Method of Half Reactions • Cr 2 O 72 -(aq) 2 Cr 3+(aq) • SO 32 -(aq) SO 42 -(aq) • How many electrons are involved in each half reaction? 4. 10 36 Copyright © Houghton Mifflin Company. All rights reserved.

Method of Half Reactions (continued) • 6 e- + Cr 2 O 72 -(aq)

Method of Half Reactions (continued) • 6 e- + Cr 2 O 72 -(aq) 2 Cr 3+(aq) • SO 32 -(aq) + SO 42 -(aq) + 2 e • How can we balance the oxygen atoms? 4. 10 37 Copyright © Houghton Mifflin Company. All rights reserved.

Method of Half Reactions (continued) • 6 e- + Cr 2 O 72 -(aq)

Method of Half Reactions (continued) • 6 e- + Cr 2 O 72 -(aq) Cr 3+(aq) + 7 H 2 O • H 2 O +SO 32 -(aq) + SO 42 -(aq) + 2 e • How can we balance the hydrogen atoms? 4. 10 38 Copyright © Houghton Mifflin Company. All rights reserved.

Method of Half Reactions (continued) • • This reaction occurs in an acidic solution.

Method of Half Reactions (continued) • • This reaction occurs in an acidic solution. 14 H+ + 6 e- + Cr 2 O 72 - 2 Cr 3+ + 7 H 2 O +SO 32 - SO 42 - + 2 e- + 2 H+ How can we balance the electrons? 4. 10 39 Copyright © Houghton Mifflin Company. All rights reserved.

Method of Half Reactions (continued) • 14 H+ + 6 e- + Cr 2

Method of Half Reactions (continued) • 14 H+ + 6 e- + Cr 2 O 72 - 2 Cr 3+ + 7 H 2 O • 3[H 2 O +SO 32 - SO 42 - + 2 e- + 2 H+] • Final Balanced Equation: Cr 2 O 72 - + 3 SO 32 - + 8 H+ 2 Cr 3+ + 3 SO 42 - + 4 H 2 O 4. 10 40 Copyright © Houghton Mifflin Company. All rights reserved.

Exercise Balance the following oxidation-reduction reaction that occurs in acidic solution. Br-(aq) + Mn.

Exercise Balance the following oxidation-reduction reaction that occurs in acidic solution. Br-(aq) + Mn. O 4 -(aq) Br 2(l)+ Mn 2+(aq) 4. 10 41 Copyright © Houghton Mifflin Company. All rights reserved.

Half-Reaction Method – Balancing in Base 1. Balance as in acid. 2. Add OH

Half-Reaction Method – Balancing in Base 1. Balance as in acid. 2. Add OH that equals H+ ions (both sides!) 3. Form water by combining H+, OH. Cancel any water molecules that appear on both sides. 4. Check elements and charges for balance. 4. 10 42 Copyright © Houghton Mifflin Company. All rights reserved.