CHAPTER 5 Reactions in Aqueous Solution

1
CHAPTER 5Reactions in Aqueous Solution

• 5.1 Properties of Compounds in Aqueous Solution
• 5.2 Precipitation reactions
• 5.3 Acids and Bases
• 5.4 Reactions of Acids and Bases
• 5.5 Gas-forming reactions
• 5.6 Classifying Reactions in Aqueous Solution
• 5.7 Oxidation-Reduction Reactions
• 5.8 Measuring Concentrations of Compounds in
  solution
• 5.9 pH, a Concentration scale for acids and bases
• 5.10 Stoichiometry of Reactions in Aqueous
  Solutions

 
2
5.1 Properties of Compounds in Aqueous Solution

• Solute
• Solvent
• Solution
• Electrodes (conductor of electricity)
• Electrolytes (ionic compound soluble in water,
  conducts electricity)
• Ions in Aqueous Solution electrolytes,
  complete/nearly complete dissociation
• Electrolytes All ionic compounds soluble in
  water
• Strong nearly complete dissociation, good
  conductor
• Weak only partial dissociation, weak conductor
• Figure 5.3, page 179 (be able to use)
• Non-electrolyte dissolve in water, but do not
  conduct

3
Water Solubility of Ionic Compounds
If one ion from the Soluble Compd. list is
present in a compound, the compound is water
soluble.
4
5.2 Precipitation reactions Writing Equations
for Aqueous Ionic Reactions

• Produces a water-insoluble product precipitate
• Writing the equation use state symbols, (s)
  denotes the precipitate
• Three types of equations are used to represent
  aqueous ionic reactions molecular, total ionic,
  and net ionic equations.
• molecular equation shows all reactants and
  products as if they were intact, un-dissociated
• total ionic equation shows all the soluble ionic
  substances dissociated into ions. Charges must
  balance
• net ionic equation it eliminates the spectator
  ions and shows the actual chemical change taking
  place.
• Spectator ions not involved in chemical change.

5
Precipitation Reactions

• The driving force is the formation of an
  insoluble compound a precipitate.
• Molecular equation
• Pb(NO3)2(aq) 2 KI(aq) -----gt
• 2 KNO3(aq) PbI2(s)
• Net ionic equation
• Pb2(aq) 2 I-(aq) ---gt PbI2(s)

6
Precipitation Reactions Predicting Whether a
Precipitate Will Form

• Predict whether a reaction occurs, and write
  balanced total and net ionic equations.
• (a) iron(III) chloride(aq) cesium
  phosphate(aq) ?
• (b) sodium hydroxide(aq) cadmium nitrate(aq)
  ?
• (c) magnesium bromide(aq) potassium
  acetate(aq) ?
• (d) silver sulfate(aq) barium chloride(aq) ?

7
Problem 5.2.1

• molecular equation
• Pb(NO3)2(aq) K2CrO4(aq) ? PbCrO4(s)
  2 KNO3(aq)
• Write the Total Ionic and Net Ionic equations
• Total
• Net

8
Problem 5.2.2

• Write the Total Ionic and Net Ionic equations for
• CaCl2(aq) Na2CO3(aq) ?
• CaCO3(s) 2 NaCl(aq)
• Total
• Net

9
Problem 5.2.3

• This problem ties in concepts from at least 3
  chapters 3, 4, 5.
• Solutions of iron (III) chloride and potassium
  hydroxide are combined.
• Naming, balancing formulas, balancing reactions,
  solubility
• Write the
• Molecular equation
• Total ionic equation
• Net ionic equation

10
Review Combining skills Problem 5.2.4

• Combine calcium chloride and potassium phosphate
• Write the molecular equation

11
Review Combining skills Problem 5.2.4

• 3 CaCl2(aq) 2 K3PO4(aq) ? Ca3PO4(s) 6
  KCl(aq)
• Write the Total Ionic and Net Ionic equations
• Combining 5 grams CaCl2 with 3.5 grams of K3PO4
  produced only a 67 yield of KCl.
• What is the limiting reactant?
• What mass of product did you make?

12
Road Map

• Where we were
• Total Net ionic equations
• Precipitation reactions
• Where we are going
• Acids and Bases
• Classifying reactions
• Oxidation reactions
• Measuring concentrations of compounds in solution
• pH
• Stoichiometry of reactions in aqueous solution

13
5.3 Acids and Bases(know table 5.2, pg 187)

• Acid increases the H concentration
• Base increases the OH- concentration
• Strong acid or base completely
  dissociates/ionizes
• Weak acid or base partial ionization
• Oxides of nonmetals and metals
• Acidic oxides (C,N,S) give H
• Basic oxides (CaO) give OH-

14
Know the strong acids bases!
15
5.4 Acid-Base Reactions

• The driving force is the formation of water.
• NaOH(aq) HCl(aq) ---gt
• NaCl(aq) H2O(liq)
• Net ionic equation
• OH-(aq) H(aq) ---gt H2O(liq)
• This applies to ALL reactions of STRONG acids and
  bases.

16
5.4 - Reactions of Acids and Bases

• An Acid reacting with a Base produces a
• salt and water
• Acid(aq) Base(aq) ? salt (s) H2O (l)
• HX MOH ---gt MX H2O
• This is one way to make compounds!
• Neutralization reaction a strong acid with a
  strong base

17
5.4 Acid-Base Reactions Neutralization

• What volume of 0.1292 M Ba(OH)2 would neutralize
  50.00 mL of 0.325 M HCl solution?

18
5.5 Gas-forming reactions

• This is primarily the chemistry of metal
  carbonates.
• CO2 and water ---gt H2CO3
• H2CO3(aq) Ca2 (aq) ---gt
• 2 H(aq) CaCO3(s) (limestone)
• Adding acid reverses this reaction.
• MCO3 acid ---gt CO2 salt

19
5.5 Gas-Forming Reactions

• CaCO3(s) H2SO4(aq) ---gt
• 2 CaSO4(s) H2CO3(aq)
• Carbonic acid is unstable and forms CO2 H2O
• H2CO3(aq) ---gt CO2 (g) water (l)
• (Antacid tablet has citric acid NaHCO3)

20
(No Transcript)
21
CHAPTER 5Reactions in Aqueous Solution

• 5.1 Properties of Compounds in Aqueous Solution
• 5.2 Precipitation reactions
• Be familiar with and know how to use the
  solubility rules
• 5.3 Acids and Bases
• 5.4 Reactions of Acids and Bases
• 5.5 Gas-forming reactions
• 5.6 Classifying Reactions in Aqueous Solution
• Know the strong acids bases, table 5.2
• 5.7 Oxidation-Reduction Reactions
• 5.8 Measuring Concentrations of Compounds in
  solution
• 5.9 pH, a Concentration scale for acids and bases
• 5.10 Stoichiometry of Reactions in Aqueous
  Solutions

Kull Chem 105 Chapter 2
 
22
5.6 Classifying reactions in aqueous solution

• Balance the following reactions and then classify
  each as precipitation (s), acid-base, or
  gas-forming reaction (g).
• a) Ba(OH)2 (aq) 2 HCl (aq) ? BaCl2 (aq)
  2 H2O (l)
• b) 2 HNO3 (aq) CoCO3 (s) ? Co(NO3)2 (aq)
  H2O (l) CO2 (g)
• c) 2 Na3PO4 (aq) 3 Cu(NO3)2 (aq) ?
  Cu3(PO4)2 (s) 6 NaNO3 (aq)

23
5.7 Oxidation-Reduction Reactions

• Oxidation any process in which oxygen is added
  to another substance gains oxygen,
• OIL Oxidation Is Loss of electrons
• RIG Reduction Is Gain of electrons
• Reducing agent gets oxidized
• Oxidizing agent gets reduced

24
5.7 Oxidation-Reduction Reactions Oxidation
Numbers ReDox Reactions

• 5-36 (pg 225) Oxidation number
• PF6- H2AsO4- UO2- N2O5 POCl5
  XeO42-
• 5-37 (a)
• Zn (s) ? Zn2 (aq) 0 ? 2 (ox)
• N5 ? N4 (aq) 5 ? 4 (red)
• O2- ? O2- (aq) no change
• H ? H (aq) no change
• Oxidation (loss of e-)
• Reduction (gain of e-)

25
5.7 Recognizing a Redox Reaction

• Corrosion of aluminum
• 2 Al(s) 3 Cu2(aq) --gt 2 Al3(aq) 3 Cu(s)
• Al(s) --gt Al3(aq) 3 e-
• Ox. no. of Al increases as e- are donated by the
  metal.
• Therefore, Al is OXIDIZED
• Al is the REDUCING AGENT in this balanced
  half-reaction.

26
5.7 Recognizing a Redox Reaction

• Notice that the 2 half-reactions add up to give
  the overall reaction if we use 2 mol of Al and 3
  mol of Cu2.
• 2 Al(s) --gt 2 Al3(aq) 6 e-
• 3 Cu2(aq) 6 e- --gt 3 Cu(s)
• ------------------------------------------------
  --------------------------------------------------
  --------------------------------
• 2 Al(s) 3 Cu2(aq) ---gt 2 Al3(aq) 3 Cu(s)
• Final eqn. is balanced for mass and charge.

27
5.7 Common Oxidizing and Reducing AgentsSee
Table 5.4
Cu HNO3 --gt Cu2 NO2
2 K 2 H2O --gt 2 KOH H2
28
5.7 Oxidation-Reduction Reactions

• Thermite reaction
• Fe2O3(s) 2 Al(s)
• ----gt 2 Fe(s) Al2O3(s)
• X Reactant Product
• Fe 3 3 e- ? 0
• O -2 ? -2
• Al 0 ? 3 3e-

29
5.8 Measuring Concentrations

• How many moles of each ion are in each solution?
• (a) 2 mol of potassium perchlorate dissolved in
  water
• (b) 354 g of magnesium acetate dissolved in
  water
• (c) 1.88 x 1024 formula units of ammonium
  chromate dissolved in water
• (d) 1.32 L of 0.55 M sodium bisulfate

30
PROBLEM You have 50.0 mL of 3.0 M NaOH and you
want 0.50 M NaOH. What do you do?

• Add water to the 3.0 M solution to lower its
  concentration to 0.50 M
• Dilute the solution!

31
PROBLEM You have 50.0 mL of 3.0 M NaOH and you
want 0.50 M NaOH. What do you do?
But how much water do we add?
32
PROBLEM You have 50.0 mL of 3.0 M NaOH and you
want 0.50 M NaOH. What do you do?

• Amount of NaOH in original solution
• M V
• (3.0 mol/L)(0.050 L) 0.15 mol NaOH
• Amount of NaOH in final solution must also 0.15
  mol NaOH
• Volume of final solution
• (0.15 mol NaOH)(1 L/0.50 mol) 0.30 L
• or 300 mL

33
PROBLEM You have 50.0 mL of 3.0 M NaOH and you
want 0.50 M NaOH. What do you do?

• Conclusion
• add 250 mL of water to 50.0 mL of 3.0 M NaOH to
  make 300 mL of 0.50 M NaOH.
  

34
5.8 Measuring Concentrations of Compounds in
Solution

• Concentration (Molarity) moles/L
• How many moles of H(aq) are present in 451 mL of
  3.20 M hydrobromic acid?
• 5-46 What volume 2.06 M KMnO4, in liters,
  contains 322 g of solute?
• 0.989 L

35
5.8 Preparing solutions of Known Concentrations

• 5-50 What mass of oxalic acid, H2C2O4, is
  required to prepare 250. mL of a solution that
  has a concentration or 0.15 M H2C2O4?
• 3.4 g H2C2O4

36
5.9 pH, a Concentration scale for acids and bases

• pH a way to express acidity -- the concentration
  of H in solution.

Low pH high H
High pH low H
Acidic solution pH lt 7 Neutral pH 7 Basic
solution pH gt 7
37
5.9 pH, a Concentration scale for acids and bases

• pH -log H
• pOH - log OH-
• Kw HOH- 1.00 x 10-14
• pH pOH 14
• 5-56 A saturated solution of milk of magnesia,
  Mg(OH)2, has a pH of 10.5. What is the hydrogen
  ion concentration of the solution? Is the
  solution acidic or basic?
• 3 x 10-11
• basic

38
H and pH

• If the H of soda is 1.6 x 10-3 M, the pH is
  ____?
• Because pH - log H then
• pH - log (1.6 x 10-3)
• pH 2.80

39
5.10 Stoichiometry of Reactions in Aqueous
Solutions

• 5-64 Hydrazine, N2H4, a base like ammonia, can
  react with an acid such as sulfuric acid. What
  mass of hydrazine reacts with 250. mL of 0.146 M
  H2SO4?
• 2 N2H4 (aq) H2SO4 (aq) ?
• 2 N2H5 (aq) SO42- (aq)
• 2.34 g N2H4

40
5.10 SOLUTION STOICHIOMETRY

• Zinc reacts with acids to produce H2 gas.
• We have 10.0 g of Zn
• What volume of 2.50 M HCl is needed to convert
  the Zn completely?

41
5.10 SOLUTION STOICHIOMETRY

• Zinc reacts with acids to produce H2 gas. If you
  have 10.0 g of Zn, what volume of 2.50 M HCl is
  needed to convert the Zn completely?
• Step 1 Write the balanced equation
• Zn(s) 2 HCl(aq) --gt ZnCl2(aq) H2(g)
• Step 2 Calculate moles of Zn

42
5.10 Zinc reacts with acids to produce H2 gas.
If you have 10.0 g of Zn, what volume of 2.50 M
HCl is needed to convert the Zn completely?

• Step 3 Use the stoichiometric factor to get
• Moles of HCl

Step 4 Calculate volume of HCl reqd
43
5.10 Standardize a solution of NaOH i.e.,
accurately determine its concentration.

• 1.065 g of H2C2O4 (oxalic acid) requires 35.62
  mL of NaOH for titration to an equivalence point.
  What is the concentration of the NaOH?

44
1.065 g of H2C2O4 (oxalic acid) requires 35.62 mL
of NaOH for titration to an equivalence point.
What is the concentration of the NaOH?

• Step 1 Calculate amount of H2C2O4

Step 2 Calculate amount of NaOH reqd
45
1.065 g of H2C2O4 (oxalic acid) requires 35.62 mL
of NaOH for titration to an equivalence point.
What is the concentration of the NaOH?

• Step 1 Calculate amount of H2C2O4
• 0.0118 mol acid
• Step 2 Calculate amount of NaOH reqd
• 0.0236 mol NaOH
• Step 3 Calculate concentration of NaOH

NaOH 0.663 M
46
5.10 Use standardized NaOH to determine the
amount of an acid in an unknown.

• Apples contain malic acid, C4H6O5.
• C4H6O5(aq) 2 NaOH(aq) ---gt
• Na2C4H4O5(aq) 2 H2O(liq)
• 76.80 g of apple requires 34.56 mL of 0.663 M
  NaOH for titration.
• What is weight of malic acid?

47
76.80 g of apple requires 34.56 mL of 0.663 M
NaOH for titration. What is weight of malic
acid?

• Step 1 Calculate moles of NaOH used.
• C V (0.663 M)(0.03456 L) 0.0229 mol NaOH
• Step 2 Calculate amount of acid titrated.
• Step 3 Calculate mass of acid titrated.
• Step 4 Calculate malic acid.

0.0115 mol acid
48
Challenge

• 5- 72
• 5- 75
• 5-76
• First 3 teams (max 4 members) to correctly solve
  the problem receive 5 bonus points

49
Next Lesson

• Quiz Chapter 5
• Chapter 6

50
Chapter 6 Principles of Reactivity Energy and
Chemical Reactivity

• Energy transfer
• Calorie burning, gravitational, chemical,
  electrostatic
• Heat- mostly seen in chemical processes
• Thermodynamics transfer of heat between
  objects science of heat and work
• Energy Some basic principles capacity to do
  work
• Kinetic energy of motion
• Potential energy of position
• Conservation of energy (aka First law of
  thermodynamics)
• Total energy of universe is constant

51
Energy Some basic principles capacity to do
work

• Systems and surroundings
• Thermal equilibrium system and surroundings
  reach same temperature
• Exothermic (heat out of system)
• Endothermic (heat into system)