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Chapter Four:
TYPES OF CHEMICAL REACTIONS AND
SOLUTION STOICHIOMETRY
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 2
Water, the Common Solvent
• One of the most important substances on earth
• Can dissolve many different substances
• A polar molecule
4.1
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 3
Dissolution of a Solid in a Liquid
4.1
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 4
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
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 5
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
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 6
Electrolyte Behavior
4.2
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 7
Chemical Reactions of Solutions
• We must know:– Nature of the reaction– Amounts of chemicals present in the solutions
4.3
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 8
Molarity
• Molarity (M) = moles of solute per volume of solution in liters:
4.3
M
M
molaritymoles of soluteliters of solution
HClmoles of HClliters of solution
362
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 9
Concept Check
Which of the following solutions containsthe greatest number of ions?
a) 400.0 mL of 0.10 M NaCl.
b) 300.0 mL of 0.10 M CaCl2.
c) 200.0 mL of 0.10 M FeCl3.
d) 800.0 mL of 0.10 M sucrose.
4.3
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 10
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
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 11
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
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 12
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
M1V1 = M2V2
4.3
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 13
Types of Chemical Reactions
• Precipitation Reactions
• Acid-Base Reactions
• Oxidation-Reduction Reactions
4.4
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 14
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
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 15
The Reaction of K2CrO4(aq) and Ba(NO3)2(aq)
4.5
• Ba2+(aq) + CrO42–(aq) → BaCrO4(s)
solid BaCrO4 formed
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 16
Precipitation of Silver Chloride
4.5
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 17
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
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 18
Simple Rules for Solubility
1. Most nitrate (NO3) salts are soluble.
2. Most alkali (group 1A) salts and NH4+ are soluble.
3. Most Cl, Br, and I salts are soluble (except Ag+, Pb2+, Hg2
2+).
4. Most sulfate salts are soluble (except BaSO4, PbSO4, Hg2SO4, CaSO4).
5. Most OH salts are only slightly soluble (NaOH, KOH are soluble, Ba(OH)2, Ca(OH)2 are marginally soluble).
6. Most S2, CO32, CrO4
2, PO43 salts are only slightly
soluble.
4.5
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 19
Describing Reactions in Solution
• Formula Equation (Molecular Equation)– Reactants and products as compounds
AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq)
• Complete Ionic Equation– All strong electrolytes shown as ions
Ag+(aq) + NO3(aq) + Na+(aq) + Cl(aq)
AgCl(s) + Na+(aq) + NO3(aq)
4.6
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 20
Describing Reactions in Solution
• Net Ionic Equation– Show only components that actually react
Ag+(aq) + Cl(aq) AgCl(s)
– Na+ and NO3 are spectator ions
4.6
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 21
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
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 22
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
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 23
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
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 24
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
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 25
Acid-Base Reactions (Brønsted-Lowry)
• Acid – proton donor
• Base – proton acceptor
• For a strong acid and base reaction:H+(aq) + OH–(aq) H2O(l)
4.8
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 26
Neutralization of a Strong Acid by a Strong Base
4.8
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 27
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
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 28
Performing Calculations for Acid-Base Reactions
1. List initial species and predict reaction.
2. Write balanced net ionic reaction.
3. Calculate moles of reactants.
4. Determine limiting reactant.
5. Calculate moles of required reactant or product.
6. Convert to grams or volume, as required.
4.8
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 29
Oxidation-Reduction Reactions (Redox Reactions)
• Reactions in which one or more electrons are transferred.
4.9
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Reaction of Sodium and Chlorine
4.9
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 31
Rules for Assigning Oxidation States
1. Oxidation state of an atom in an element = 0
2. Oxidation state of monatomic element = charge
3. Oxygen = 2 in covalent compounds (except in peroxides where it = 1)
4. Hydrogen = +1 in covalent compounds
5. Fluorine = 1 in compounds
6. Sum of oxidation states = 0 in compounds
7. Sum of oxidation states = charge of the ion
4.9
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 32
Exercise
Find the oxidation states for each of the elements in each of the following compounds:
• K2Cr2O7
• CO32-
• MnO2
• PCl5• SF4
4.9
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 33
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
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 34
Concept Check
Which of the following are oxidation-reduction reactions? Identify the oxidizing agent and the reducing agent.
a) Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g)
b) Cr2O72-(aq) + 2OH-(aq) 2CrO4
2-(aq) + H2O(l)
c) 2CuCl(aq) CuCl2(aq) + Cu(s)
4.9
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 35
Balancing Oxidation-Reduction Reactions
• Cr2O72-(aq) + SO3
2-(aq) Cr3+(aq) + SO42-(aq)
• How can we balance this equation?
• First Steps:– Separate into half-reactions– Balance elements except H and O
4.10
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 36
Method of Half Reactions
• Cr2O72-(aq) 2Cr3+(aq)
• SO32-(aq) SO4
2-(aq)
• How many electrons are involved in each half reaction?
4.10
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 37
Method of Half Reactions (continued)
• 6e- + Cr2O72-(aq) 2Cr3+(aq)
• SO32-(aq) + SO4
2-(aq) + 2e-
• How can we balance the oxygen atoms?
4.10
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 38
Method of Half Reactions (continued)
• 6e- + Cr2O72-(aq) Cr3+(aq) + 7H2O
• H2O +SO32-(aq) + SO4
2-(aq) + 2e-
• How can we balance the hydrogen atoms?
4.10
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 39
Method of Half Reactions (continued)
• This reaction occurs in an acidic solution.
• 14H+ + 6e- + Cr2O72- 2Cr3+ + 7H2O
• H2O +SO32- SO4
2- + 2e- + 2H+
• How can we balance the electrons?
4.10
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 40
Method of Half Reactions (continued)
• 14H+ + 6e- + Cr2O72- 2Cr3+ + 7H2O
• 3[H2O +SO32- SO4
2- + 2e- + 2H+]
• Final Balanced Equation:Cr2O7
2- + 3SO32- + 8H+ 2Cr3+ + 3SO4
2- + 4H2O
4.10
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 41
Exercise
Balance the following oxidation-reduction reaction that occurs in acidic solution.
Br-(aq) + MnO4-(aq) Br2(l)+ Mn2+(aq)
4.10
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 4 | Slide 42
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