Additional Aspects of Aqueous Equilibria. Reaction of Weak Bases with Water The base reacts with...
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Transcript of Additional Aspects of Aqueous Equilibria. Reaction of Weak Bases with Water The base reacts with...
Additional Aspects Additional Aspects of Aqueous of Aqueous EquilibriaEquilibria
Reaction of Weak Bases with Reaction of Weak Bases with WaterWater
The base reacts with water, producing The base reacts with water, producing its conjugate acid and hydroxide ion:its conjugate acid and hydroxide ion:
CH3NH2 + H2O CH3NH3+ + OH- Kb = 4.38 x 10-
4
4 3 3
3 2
[ ][ ]4.38 10
[ ]b
CH NH OHK x
CH NH
KKbb for Some Common Weak for Some Common Weak BasesBases
Base FormulaConjugat
e AcidKb
Ammonia NH3 NH4+ 1.8 x 10-5
Methylamine CH3NH2 CH3NH3+ 4.38 x 10-4
Ethylamine C2H5NH2 C2H5NH3+ 5.6 x 10-4
Diethylamine (C2H5)2NH (C2H5)2NH2+ 1.3 x 10-3
Triethylamine (C2H5)3N (C2H5)3NH+ 4.0 x 10-4
Hydroxylamine HONH2 HONH3+
1.1 x 10-8
Hydrazine H2NNH2 H2NNH3+
3.0 x 10-6
Aniline C6H5NH2 C6H5NH3+
3.8 x 10-10
Pyridine C5H5N C5H5NH+ 1.7 x 10-9
Many students struggle with identifying weak bases and their conjugate acids.What patterns do you see that may help you?
Reaction of Weak Bases with Reaction of Weak Bases with WaterWater
The generic reaction for a base The generic reaction for a base reacting with water, producing its reacting with water, producing its conjugate acid and hydroxide ion:conjugate acid and hydroxide ion:
B + H2O BH+ + OH-
[ ][ ]
[ ]b
BH OHK
B
(Yes, all weak bases do this – DO (Yes, all weak bases do this – DO NOTNOTendeavor to make this endeavor to make this complicated!)complicated!)
Buffered SolutionsBuffered Solutions
A solution that resists a change A solution that resists a change in pH when either hydroxide ions in pH when either hydroxide ions oror protons are added. protons are added.
Buffered solutions contain either:Buffered solutions contain either: A weak acid and its saltA weak acid and its salt A weak base and its saltA weak base and its salt
Acid/Salt Buffering PairsAcid/Salt Buffering Pairs
Weak AcidFormula
of the acidExample of a salt of the
weak acid Hydrofluoric HF KF – Potassium fluoride
Formic HCOOH KHCOO – Potassium formate
Benzoic C6H5COOH NaC6H5COO – Sodium benzoate
Acetic CH3COOH NaH3COO – Sodium acetate
Carbonic H2CO3 NaHCO3 - Sodium bicarbonate
Propanoic HC3H5O2 NaC3H5O2 - Sodium propanoate
Hydrocyanic HCN KCN - potassium cyanide
The salt will contain the anion of the The salt will contain the anion of the acid, and the cation of a strong base acid, and the cation of a strong base ((NaNaOH, OH, KKOH)OH)
Base/Salt Buffering PairsBase/Salt Buffering PairsThe salt will contain the cation of the The salt will contain the cation of the base, and the anion of a strong acid base, and the anion of a strong acid (H(HClCl, H, HNONO33))
BaseFormula of the base
Example of a salt of the weak acid
Ammonia NH3 NH4Cl - ammonium chloride
Methylamine
CH3NH2
CH3NH2Cl – methylammonium chloride
Ethylamine C2H5NH2
C2H5NH3NO3 - ethylammonium nitrate
Aniline C6H5NH2 C6H5NH3Cl – aniline hydrochloride
Pyridine C5H5N C5H5NHCl – pyridine hydrochloride
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0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 45.00m illiliters NaOH (0.10 M)
pH
Titration of an Unbuffered Titration of an Unbuffered SolutionSolution
A solution that is 0.10 M CH3COOH is titrated with 0.10 M NaOH
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m illiliters NaOH (0.10 M)
pH
Titration of a Buffered Titration of a Buffered SolutionSolution
A solution that is 0.10 M CH3COOH and 0.10 M NaCH3COO is titrated with 0.10 M NaOH
Comparing ResultsComparing Results
Graph
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0 5 10 15 20 25 30 35 40 45
mL 0.10 M NaOH
pH
BufferedBuffered
UnbufferedUnbuffered
Comparing ResultsComparing Results
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0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 45.00
m illiliters NaOH (0.10 M)
pH
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0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 45.00m illiliters NaOH (0.10 M)
pH
Unbuffered Buffered
In what ways are the graphs different?In what ways are the graphs similar?
Henderson-Hasselbalch Henderson-Hasselbalch EquationEquation
][
][log
][
][log
acid
basepK
HA
ApKpH aa
[ ] [ ]log log
[ ] [ ]b b
BH acidpOH pK pK
B base
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0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 45.00m illiliters NaOH (0.10 M)
pH
Weak Acid/Strong Base Weak Acid/Strong Base TitrationTitration
A solution that is 0.10 M CH3COOH is titrated with 0.10 M NaOH
Endpoint is above pH 7
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m illiliters NaOH (0.10 M)
pH
Strong Acid/Strong Base Strong Acid/Strong Base TitrationTitration
A solution that is 0.10 M HCl is titrated with 0.10 M NaOH
Endpoint is at pH 7
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m illiliters HCl (0.10 M)
pH
Strong Acid/Strong Base Strong Acid/Strong Base TitrationTitration
A solution that is 0.10 M NaOH is titrated with 0.10 M HCl
Endpoint is at pH 7 It is important to
recognize that titration curves are not always increasing from left to right.
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m illiliters NH3 (0.10 M)
pH
Strong Acid/Weak Base Strong Acid/Weak Base TitrationTitration
A solution that is 0.10 M HCl is titrated with 0.10 M NH3
Endpoint is below pH 7
Selection of Selection of IndicatorsIndicators
Some Acid-Base IndicatorsSome Acid-Base IndicatorsIndicator
pH Range in whichColor Change Occurs
Color Changeas pH Increases
Crystal violetThymol blueOrange IVMethyl orangeBromcresol greenMethyl redChlorophenol redBromthymol bluePhenol redNeutral redThymol bluePhenolphthaleinThymolphthaleinAlizarin yellowIndigo carmine
0.0 - 1.61.2 - 2.81.4 - 2.83.2 - 4.43.8 - 5.44.8 - 6.25.2 - 6.86.0 - 7.66.6 - 8.06.8 - 8.08.0 - 9.6
8.2 - 10.09.4 - 10.6
10.1 - 12.011.4 - 13.0
yellow to bluered to yellowred to yellowred to yellowyellow to bluered to yellowyellow to redyellow to blueyellow to redred to amberyellow to bluecolourless to pinkcolourless to blueyellow to blueblue to yellow
pH pH IndicatorIndicator
s s and theirand theirrangesranges
KKspsp Values for Some Salts at Values for Some Salts at 2525CC
Name Formula Ksp
Barium carbonate BaCO3 2.6 x 10-9
Barium chromate BaCrO4 1.2 x 10-10
Barium sulfate BaSO4 1.1 x 10-10
Calcium carbonate CaCO3 5.0 x 10-9
Calcium oxalate CaC2O4 2.3 x 10-9
Calcium sulfate CaSO4 7.1 x 10-5
Copper(I) iodide CuI 1.3 x 10-12
Copper(II) iodate Cu(IO3)2 6.9 x 10-8
Copper(II) sulfide CuS 6.0 x 10-37
Iron(II) hydroxide Fe(OH)2 4.9 x 10-17
Iron(II) sulfide FeS 6.0 x 10-19
Iron(III) hydroxide Fe(OH)3 2.6 x 10-39
Lead(II) bromide PbBr2 6.6 x 10-6
Lead(II) chloride PbCl2 1.2 x 10-5
Lead(II) iodate Pb(IO3)2 3.7 x 10-13
Lead(II) iodide PbI2 8.5 x 10-9
Lead(II) sulfate PbSO4 1.8 x 10-8
Name Formula Ksp
Lead(II) bromide PbBr2 6.6 x 10-6
Lead(II) chloride PbCl2 1.2 x 10-5
Lead(II) iodate Pb(IO3)2 3.7 x 10-13
Lead(II) iodide PbI2 8.5 x 10-9
Lead(II) sulfate PbSO4 1.8 x 10-8
Magnesium carbonate MgCO3 6.8 x 10-6
Magnesium hydroxide Mg(OH)2 5.6 x 10-12
Silver bromate AgBrO3 5.3 x 10-5
Silver bromide AgBr 5.4 x 10-13
Silver carbonate Ag2CO3 8.5 x 10-12
Silver chloride AgCl 1.8 x 10-10
Silver chromate Ag2CrO4 1.1 x 10-12
Silver iodate AgIO3 3.2 x 10-8
Silver iodide AgI 8.5 x 10-17
Strontium carbonate SrCO3 5.6 x 10-10
Strontium fluoride SrF2 4.3 x 10-9
Strontium sulfate SrSO4 3.4 x 10-7
Zinc sulfide ZnS 2.0 x 10-25
Solving Solubility ProblemsSolving Solubility Problems
For the salt AgI at 25C, Ksp = 1.5 x 10-16
AgI(s) Ag+(aq) + I-(aq)
I
C
E
OO
+x +x
x x
1.5 x 10-16 = x2
x = solubility of AgI in mol/L = 1.2 x 10-8 M
Solving Solubility ProblemsSolving Solubility Problems
For the salt PbCl2 at 25C, Ksp = 1.6 x 10-
5PbCl2(s) Pb2+(aq) + 2Cl-(aq)
I
C
E
OO
+x +2x
x 2x
1.6 x 10-5 = (x)(2x)2 = 4x3
x = solubility of PbCl2 in mol/L = 1.6 x 10-2 M
Solving Solubility with a Common Solving Solubility with a Common IonIon
For the salt AgI at 25C, Ksp = 1.5 x 10-16
What is its solubility in 0.05 M NaI?
AgI(s) Ag+(aq) + I-(aq)
I
C
E
0.05O
+x 0.05+x
x 0.05+x
1.5 x 10-16 = (x)(0.05+x) (x)(0.05)
x = solubility of AgI in mol/L = 3.0 x 10-15 M
Precipitation and Qualitative Precipitation and Qualitative AnalysisAnalysis
Complex IonsComplex Ions
A Complex ion is a charged species composed of:
1. A metallic cation
2. Ligands – Lewis bases that have a lone electron pair that can form a covalent bond with an empty orbital belonging to the metallic cation
NHNH33, CN, CN--, and H, and H22O O are Common Ligandsare Common Ligands
O
H
HNH
HH
C N-
Coordination NumberCoordination Number Coordination number refers to the number of ligands attached to the cation 2, 4, and 6 are the most common coordination numbersCoordinatio
n number
Example(s)
2 Ag(NH3)2+
4 CoCl42- Cu(NH3)42+
6 Co(H2O)62+ Ni(NH3)6
2+
Complex Ions and SolubilityComplex Ions and Solubility
AgCl(s) Ag+ + Cl- Ksp = 1.6 x 10-10
Ag+ + NH3 Ag(NH3)+ K1 = 2.1 x 103
Ag(NH3)+ NH3 Ag(NH3)2+ K2 = 8.2 x 103
AgCl + 2NH3 Ag(NH3)2+ +
Cl-K = KspK1K2
23
233
][
]][)([108.2
NH
ClNHAgxK