1. Reactions in Aqueous Solution
Cornell Notes
Chapter 4
Reactions in Aqueous Solution

2. Warm Up
Pour the two solutions together. Observe what happens. Discuss with people at your table why this happens.

3. Plan for Today
Discussion: What would make this class better? What would you like to see me do differently to help you be more successful?
Lecture Notes and How to Write Them
Practice Problems

4. Today’s Lecture Notes Topics: What’s Important?
Definitions:
Electrolyte (strong vs. weak)
Non-electrolyte
Dissociate
Precipitate
Solubility ( and guideline table)
Metathesis Reactions
Types of Equations:
Molecular
Complete ionic
Net ionic
Neutralization
Strong Acids vs. Strong Bases

5. Today’s Lecture Notes Topics: What’s Important?
Processes
How to identify strong vs. weak electrolytes
How to predict precipitates and metathesis reactions
How to write a molecular equation
How to write a net ionic equation
How to write a neutralization reaction

6. What do I need to memorize and what do I need to just practice with?
Memorize Practice
Definitions Solubility Guidelines
Table 4.2, p Activity Series, p. 144
Table 4.3, p Steps for Molecular Eq
Molarity equation Steps for Net Ionic Eq
Dilution equation Steps for Neutralization

7. Solutions
Solutions are defined as homogeneous mixtures of two or more pure substances.
The solvent is present in greatest abundance.
All other substances are solutes.
When water is the solvent, the solution is called an aqueous solution.

8. Aqueous Solutions Substances can dissolve in water by different ways:
Ionic Compounds dissolve by dissociation, where water surrounds the separated ions.
Molecular compounds interact with water, but most do NOT dissociate.
Some molecular substances react with water when they dissolve.

9. Aqueous Solutions

10. Electrolytes and Nonelectrolytes
An electrolyte is a substance that dissociates into ions when dissolved in water.
A nonelectrolyte may dissolve in water, but it does not dissociate into ions when it does so.

11. Electrolytes
A strong electrolyte dissociates completely when dissolved in water.
A weak electrolyte only dissociates partially when dissolved in water.
A nonelectrolyte does NOT dissociate in water.

12. Give it some thought
Which solute will cause the light bulb to glow most brightly, CH3OH, NaOH, or CH3COOH?

13. Warm Up 11/24
If you have an aqueous solution that contains 2.3 moles of Pb(NO3)2 , how many total moles of ions are in the solution?
2.3
4.6
6.9
9.2
Pb2+
NO3-
NO3-

14. Solubility of Ionic Compounds
Not all ionic compounds dissolve in water.
A list of solubility rules is used to decide what combination of ions will dissolve.

15. (See Solubility Rules)
Aqueous Solutions
Soluable Compounds
(See Solubility Rules)
Electrolytes
Strong
Weak
Non-Electrolytes
All soluable ionics
Strong Acids
Weak acids
Weak bases
Molecular compounds

16. Precipitation Reactions
When two solutions containing soluble salts are mixed, sometimes an insoluble salt will be produced. A salt “falls” out of solution, like snow out of the sky. This solid is called a precipitate.

17. Predicting Precipitation Reactions
Identify ions present in the reactants
Consider the cation-anion combinations
Use Solubility table to determine if these combinations are soluable or insoluable

18. Which of these are soluable?
(NH4)2S, CaCO3, NaOH, Ag2SO4, Pb(CH3COOH)2

19. Predict the identity of the precipitate…
When MgCl2 and CaS are mixed.
Write the balanced equation.

20. Predict the identity of the precipitate…
When solutions of Fe2(SO4)3 and LiOH are mixed.
Write the balanced equation.

21. Yes or No?
Will a precipitate form when Ba(NO3)2 and KOH are mixed?

22. Review
Acetic acid, CH3COOH, is extremely soluable in water, but is a weak electrolyte. How is this possible?
A strong electrolyte dissociates completely when dissolved in water.
A weak electrolyte only dissociates partially when dissolved in water.
A nonelectrolyte does NOT dissociate in water.

23. METATHESIS REACTIONS Molecular Equations Complete Ionic Equations
Net Ionic Equations
Neutralization Reactions
Gas Forming Reactions

24. Metathesis (Exchange) Reactions
Metathesis comes from a Greek word that means “to transpose.”
It appears as though the ions in the reactant compounds exchange, or transpose, ions, as seen in the equation below.
AgNO3(aq) + KCl(aq)  AgCl(s) + KNO3(aq)

25. Completing and Balancing Metathesis Equations
Steps to follow
Use the chemical formulas of the reactants to determine which ions are present.
Write formulas for the products: cation from one reactant, anion from the other. Use charges to write proper subscripts.
Check your solubility rules. If either product is insoluble, a precipitate forms.
Balance the equation.

26. Warm Up 11/30 Which set includes only substances that produce electrolytes in water?
NaBr, KCl, MgSO4
C6H12O6, CH3OH, C6H6
HCl, NH3, Cl2, N2
SiO2, CaCO3, H2SO4
Answer: a

27. Which set includes only substances that produce electrolytes in water?
NaBr, KCl, MgSO4
C6H12O6, CH3OH, C6H6
HCl, NH3, Cl2, N2
SiO2, CaCO3, H2SO4
Answer: a

28. Pb(NO3)2 + 2 KI  PbI2 + 2 KNO3 The physical evidence that the above reaction occurs is
an explosion.
the formation of a gas.
that the solution boils.
the formation of a precipitate.
Answer: d

29. Pb(NO3)2 + 2 KI  PbI2 + 2 KNO3 The physical evidence that the above reaction occurs is
an explosion.
the formation of a gas.
that the solution boils.
the formation of a precipitate.
Answer: d

30. H2SO4 and NaOH HNO3 and CaCl2 Ba(NO3)2 and Na3PO4 LiCl and SrI2
Which pair of compounds will produce a precipitate if solutions of appropriate concentrations are mixed together?
H2SO4 and NaOH
HNO3 and CaCl2
Ba(NO3)2 and Na3PO4
LiCl and SrI2
Answer: c

31. H2SO4 and NaOH HNO3 and CaCl2 Ba(NO3)2 and Na3PO4 LiCl and SrI2
Which pair of compounds will produce a precipitate if solutions of appropriate concentrations are mixed together?
H2SO4 and NaOH
HNO3 and CaCl2
Ba(NO3)2 and Na3PO4
LiCl and SrI2
Answer: c

32. Today’s Lecture Notes Topics: What’s Important?
Definitions:
Metathesis Reactions
Types of Equations:
Molecular
Complete ionic
Net ionic
Neutralization
Strong Acids vs. Strong Bases
Activity Series
Oxidation Reduction Reactions (Redox)
Displacement Reactions

33. Today’s Lecture Notes Topics: What’s Important?
Processes
How to identify strong vs. weak electrolytes
How to predict precipitates and metathesis reactions
How to write a molecular equation
How to write a net ionic equation
How to write a neutralization reaction
How to write a redox (oxidation-reduction) reaction

34. What do I need to memorize and what do I need to just practice with?
Memorize Practice
Definitions Solubility Guidelines
Table 4.2, p Activity Series, p. 144
Table 4.3, p Steps for Molecular Eq
Molarity equation Steps for Net Ionic Eq
Dilution equation Steps for Neutralization
Oxidation-Reduction Redox Problems

35. Ways to Write Metathesis Reactions
Molecular
Net Ionic
Complete Ionic

36. AgNO3(aq) + KCl(aq)  AgCl(s) + KNO3(aq)
Molecular Equation
The molecular equation lists the reactants and products without indicating the ionic nature of the compounds.
AgNO3(aq) + KCl(aq)  AgCl(s) + KNO3(aq)

37. Complete Ionic Equation
In the complete ionic equation all strong electrolytes (strong acids, strong bases, and soluble ionic salts) are dissociated into their ions.
This more accurately reflects the species that are found in the reaction mixture.
Ag+(aq) + NO3−(aq) + K+(aq) + Cl−(aq) 
AgCl(s) + K+(aq) + NO3−(aq)

38. Net Ionic Equation
To form the net ionic equation, cross out anything that does not change from the left side of the equation to the right.
The ions crossed out are called spectator ions, K+ and NO3−, in this example.
The remaining ions are the reactants that form the product—an insoluble salt in a precipitation reaction, as in this example.
Ag+(aq) + NO3−(aq) + K+(aq) + Cl−(aq) 
AgCl(s) + K+(aq) + NO3−(aq)

39. Writing Net Ionic Equations
Write a balanced molecular equation.
Dissociate all strong electrolytes.
Cross out anything that remains unchanged from the left side to the right side of the equation.
Write the net ionic equation with the species that remain.

40. Writing Net Ionic Equations
Write the net ionic equation for the reaction that occurs when aqueous solutions of silver nitrate and potassium phosphate are mixed.

41. Acids
The Swedish physicist and chemist S. A. Arrhenius defined acids as substances that increase the concentration of H+ when dissolved in water.
Both the Danish chemist J. N. Brønsted and the British chemist T. M. Lowry defined them as proton donors.

42. Bases
Arrhenius defined bases as substances that increase the concentration of OH− when dissolved in water.
Brønsted and Lowry defined them as proton acceptors (react with H+)

43. Strong or Weak?
Strong acids completely dissociate in water; weak acids only partially dissociate.
Strong bases dissociate to metal cations and hydroxide anions in water; weak bases only partially react to produce hydroxide anions.

44. Learning Check

45. Strong vs. Weak Electrolytes
If we remember the common strong acids and bases (table 4.2) and that NH3 is a weak base, we can make reasonable predictions about the electrolytic strength of a lot of compounds!

46. Acid-Base Reactions
In an acid–base reaction, the acid (H2O above) donates a proton (H+) to the base (NH3 above).
Reactions between an acid and a base are called neutralization reactions.
When the base is a metal hydroxide, water and a salt (an ionic compound) are produced.

47. Ways to Write Metathesis Reactions
Molecular
Neutralization Reactions
(Not all form precipitate!)
Net Ionic
Complete Ionic

48. Neutralization Reactions
When a strong acid (like HCl) reacts with a strong base (like NaOH), the net ionic equation is circled below:
HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l)
H+(aq) + Cl−(aq) + Na+(aq) + OH−(aq) 
Na+(aq) + Cl−(aq) + H2O(l)
H+(aq) + OH−(aq)  H2O(l)

49. K+ and NO3–. H+ and OH–. H+ and NO3–. K+ and OH–.
Warm Up 12/2 When nitric acid is neutralized by potassium hydroxide, the spectator ions are
K+ and NO3–.
H+ and OH–.
H+ and NO3–.
K+ and OH–.
Answer: a

50. K+ and NO3–. H+ and OH–. H+ and NO3–. K+ and OH–.
When nitric acid is neutralized by potassium hydroxide, the spectator ions are
K+ and NO3–.
H+ and OH–.
H+ and NO3–.
K+ and OH–.
Answer: a

51. Warm Up 12/2 Which compound below is not a strong acid?
HC2H3O2
H2SO4
HNO3
HBr
Answer: a

52. Which compound below is not a strong acid?
HC2H3O2
H2SO4
HNO3
HBr
Answer: a

53. Learning Check
a) Write the balanced molecular equation for the reaction between aqueous solutions of acetic acid, HC2H3O2, and barium hydroxide, Ba(OH)2.
b) Write the net ionic equation for this reaction

54. Learning Check
a) Write the balanced molecular equation for the reaction between aqueous solutions of acetic acid, HC2H3O2, and barium hydroxide, Ba(OH)2.
2HC2H3O2(aq) + Ba(OH)2 (aq)  Ba(C2H3O2)2(aq)+ 2H2O(l)
b) Write the net ionic equation for this reaction
2H+(aq) + 2 C2H3O2-(aq) + Ba2+(aq) + 2 OH-(aq)  Ba2+(aq) + 2 C2H3O2-(aq) H2O (l)
2H+(aq) + 2 OH-(aq)  + 2H2O (l)

55. Gas-Forming Reactions
Some metathesis reactions do not give the product expected.
When a carbonate or bicarbonate reacts with an acid, the products are a salt, carbon dioxide, and water.
CaCO3(s) + 2 HCl(aq) CaCl2(aq) + CO2(g) + H2O(l)
NaHCO3(aq) + HBr(aq) NaBr(aq) + CO2(g) + H2O(l)
Na2S(aq) + H2SO4(aq)  Na2SO4(aq) + H2S(g)

56. Metathesis Reactions Gas Forming Molecular Neutralization Reactions
(Not all form precipitate!)
Complete Ionic
Net Ionic

57. OXIDATION – REDUCTION (REDOX REACTIONS)

58. Oxidation-Reduction Reactions
Loss of electrons is oxidation.
Gain of electrons is reduction.
One cannot occur without the other.
The reactions are often called redox reactions.

59. Oxidation-Reduction Reactions

60. Oxidation Numbers
To determine if an oxidation–reduction reaction has occurred, we assign an oxidation number to each element in a neutral compound or charged entity.

61. Rules to Assign Oxidation Numbers
Elements in their elemental form have an oxidation number of zero.
The oxidation number of a monatomic ion is the same as its charge.

62. Rules to Assign Oxidation Numbers
Nonmetals tend to have negative oxidation numbers, although some are positive in certain compounds or ions.
Oxygen has an oxidation number of −2, except in the peroxide ion, in which it has an oxidation number of −1.
Hydrogen is −1 when bonded to a metal, +1 when bonded to a nonmetal.

63. Rules to Assign Oxidation Numbers
Nonmetals tend to have negative oxidation numbers, although some are positive in certain compounds or ions.
Fluorine always has an oxidation number of −1.
The other halogens have an oxidation number of −1 when they are negative; they can have positive oxidation numbers, most notably in oxyanions (ex. Chlorate)

64. Rules to Assign Oxidation Numbers
The sum of the oxidation numbers in a neutral compound is zero.
The sum of the oxidation numbers in a polyatomic ion is the charge on the ion.

65. Warm Up – Look at Oxidation Number Rules
What is the oxidation state of Phosphorous in P2O5?
What is the oxidation state of Hydrogen in NaH?
What is the oxidation state of Chromium in Cr2O72- ?
What is the oxidation state of tin in SnBr4?
What is the oxidation state of Oxygen in BaO2?

66. What is the oxidation state of Phosphorous in P2O5
What is the oxidation state of Phosphorous in P2O5? = -5, because each oxygen has a -2 charge.
What is the oxidation state of Hydrogen in NaH? = -1, because hydrogen bonded to a metal is -1, +1 when bonded to a non-metal
What is the oxidation state of Chromium in Cr2O72- ? = +6, because each oxygen is -2 and the charge of the ion is -2 overall
What is the oxidation state of tin in SnBr4? = +4, because Br oxidation state is -1
What is the oxidation state of Oxygen in BaO2? = -2, because O2 is the peroxide ion

67. DISPLACEMENT REACTIONS and ACTIVITY SERIES

68. Displacement Reactions
In displacement reactions, ions oxidize an element.
In this reaction, silver ions oxidize copper metal:
Cu(s) + 2 Ag+(aq)  Cu2+(aq) + 2 Ag(s)
The reverse reaction does NOT occur. Why not?

69. Activity Series
Elements higher on the activity series are more reactive.
They are more likely to exist as ions.
Any metal on the list can be oxidized by the ions of the metal below it

70. Metal/Acid Displacement Reactions
The elements above hydrogen will react with acids to produce hydrogen gas.
The metal is oxidized to a cation.

71. Learning Check
Which of the following metals will be oxidized by Pb(NO3)2?
Zn, Cu, or Fe?
Write the balanced molecular equation for one.
Write the net ionic equation

72. Learning Check
Which of the following metals will be oxidized by Pb(NO3)2?
Zn, Cu, or Fe? Because Fe and Zn are above Pb on the activity series.
Write the balanced molecular equation for one:
Pb(NO3)2 (aq) + Zn(s)  Pb(s) + Zn(NO3)2 (aq)
Write the net ionic equation
Pb2+(aq) + Zn(s)  Pb(s) + Zn2+(aq)

73. MOLARITY and DILLUTION

74. volume of solution in liters
Molarity
The quantity of solute in a solution can matter to a chemist.
We call the amount dissolved its concentration.
Molarity is one way to measure the concentration of a solution:
moles of solute
volume of solution in liters
Molarity (M) =

75. Molarity Check
Which is more concentrated, a solution prepare by dissolving 21.0 grams of NaF (0.500 mol) in enough water to make 500 mL of solution, or a solution prepared dissolving 10.5 g (0.250 mol) of NaF in enough water to mak 100 mL of solution?
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76. Molarity Check
Which is more concentrated, a solution prepare by dissolving 21.0 grams of NaF (0.500 mol) in enough water to make 500 mL of solution, or a solution prepared dissolving 10.5 g (0.250 mol) of NaF in enough water to mak 100 mL of solution? 21.0 g (0.500 mol) in 500 mL mol / L = 1 M 10.5 g (0.250 mol) in 100 mL mol / 0.1L = 2.5 M
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77. Mixing a Solution
To create a solution of a known molarity, weigh out a known mass (and, therefore, number of moles) of the solute.
Then add solute to a volumetric flask, and add solvent to the line on the neck of the flask.

78. Molarity Check
What is the molar concentration of K+ ions in a M solution of potassium carbonate?
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79. Molarity Check
What is the concentration of ammonia in a solution made by dissolving 3.75 grams of ammonia in L of water? How many grams of Na2SO4are there in 15 mL of 0.50 M Na2SO4? How many mL of 0.50 M Na2SO4 solution are needed to provide mol of this salt?
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80. Dilution One can also dilute a more concentrated solution by
using a pipet to deliver a volume of the solution to a new volumetric flask, and
adding solvent to the line on the neck of the new flask.

81. Dilution
The molarity of the new solution can be determined from the equation
Mc  Vc = Md  Vd,
where Mc and Md are the molarity of the concentrated and dilute solutions, respectively, and Vc and Vd are the volumes of the two solutions.

82. Dilution: Check 1.75 mL 8.75 mL 48.6 mL 57.1 mL 28570 mL
What volume of a 1.00 M stock solution of glucose must be used to make 500 mL of a 1.75 x 10-2 M glucose solution?
1.75 mL
8.75 mL
48.6 mL
57.1 mL
28570 mL

83. Using Molarities in Stoichiometric Calculations

84. Titration
A titration is an analytical technique in which one can calculate the concentration of a solute in a solution.

85. Titration
A solution of known concentration, called a standard solution, is used to determine the unknown concentration of another solution.
The reaction is complete at the equivalence point.

86. Making Hot Chocoalte!
Make a cup of hot chocolate using exactly 28.0 g of chocolate mix in 200 mL of hot water. Then do the following calculations:
According to the nutrition label, there are exactly 23.0 g of sucrose (sugar) in the sample. What is the molar concentration of sucrose in your drink?
According the the nutrition label, there are 5.0 mg of “sodium” in your sample. This “sodium” is NaCl. Calculate the molarity of the sodium ion in your drink.