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CHAPTER 5 Reactions in Aqueous Solution

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Title: 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
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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)
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