Download - Chapter 6 Problems
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Chapter 6 Problems
6-29, 6-31, 6-39, 6.41, 6-42, 6-48,
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6-29
Distinguish between Lewis Acids/Bases & Bronsted-Lowry acids and bases. Give an example.
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6-31.
Why is the pH of water usually < 7? How can you prevent this from happening?
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6-39.
The equilibrium constant for autoprotolysis of water is 1.0 x 10-14 at 25oC. What is the value of K for 4 H2O 4H+ + 4OH-
K = [H+]4 [OH]4
K = (1x10-7)4(1x10-7)4
K = 1 x 10-56
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6-41
Use Le Chatelier’s principle and Kw in Table 6-1 to decide whether the autoprotolysis of water is exothermic or endothermic at 25oC 100oC 300oC
0
1E-12
2E-12
3E-12
4E-12
5E-12
6E-12
7E-12
0 100 200 300 400
Temp
K
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6-42
Make a list of strong acid and strong bases. Memorize this list.
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6-48 Which is the stronger acid?
Dichloracetic acid Chloroacetic acidKa = 8 x 10-2 Ka = 1.36 x 10-3
Stronger Base?
Hydrazine UreaKb = 1.1 x 10-6 Kb = 1.5 x 10-14
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Chapter 8
ActivityActivity
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HomeworkHomeworkChapter 8 - Chapter 8 - ActivityActivity
8.2, 8.3, 8.6, 8.9, 8.10, 8.12
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8-1 Effect of Ionic Strength 8-1 Effect of Ionic Strength on Solubility of Saltson Solubility of Salts
Consider a saturated solution of Hg2(IO3)2 in ‘pure water’. Calculate the concentration of mercurous ions.
Hg2(IO3)2(s) Hg22+ + 2IO3
- Ksp=1.3x10-18
A seemingly strange effectseemingly strange effect is observed when a salt such as KNO3 is added. As more KNO3 is added to the solution, more
solid dissolves until [Hg22+] increases to 1.0 x 10-6 M. Why?
1823
22 103.1]][[ IOHgK sp
IICCEE
somesome -- - --x-x +x+x +2x+2xsome-xsome-x +x+x +2x+2x
182 103.1]2][[ xxK sp7109.6][ x
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Increased solubility
Why? LeChatelier’s Principle?
NO – not a product nor reactant Complex Ion?
No Hg2
2+ and IO3- do not form complexes
with K+ or NO3-.
How else?
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The Explanation
Consider Hg22+ and the IO3
-
-2+
Electrostatic attraction
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The Explanation
Consider Hg22+ and the IO3
-
2+
Electrostatic attraction
-
Hg2(IO3)2(s) The Precipitate!!The Precipitate!!
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The Explanation
Consider Hg22+ and the IO3
-
-2+
Electrostatic attraction
Add KNO3
NO3-K+
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The Explanation
Consider Hg22+ and the IO3
-
-2+
Add KNO3
K+K+
K+K+
K+K+
NO3-
NO3-
NO3-
NO3-
NO3-
NO3-
NO3-
NO3-
NO3-
NO3-
K+K+
K+K+
K+ K+
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The Explanation
Consider Hg22+ and the IO3
-
2+
NO3-
NO3-
NO3-
NO3-
NO3-
NO3-
NO3-
NO3-
NO3-
NO3-
Hg22+ and IO3
- can’t getCLOSE ENOUGH to form Crystal latticeOr at least it is a lot “Harder” to form crystal lattice
-
K+ K+
K+K+
K+K+
K+K+
K+K+
K+ K+
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The potassium hydrogen tartrate example
K+-O
O
OH
OH
O
OH
potassium hydrogen tartrate
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Alright, what do we mean by Ionic strength?
Consider Hg22+ and the IO3
-
-2+
Add KNO3
K+K+
K+K+
K+K+
NO3-
NO3-
NO3-
NO3-
NO3-
NO3-
NO3-
NO3-
NO3-
NO3-
K+K+
K+K+
K+ K+
Low Ionic StrengthHigher Ionic StrengthHigh Ionic Strength
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Alright, what do we mean by Ionic strength?
Ionic strength is a measure of the total measure of the total concentration of ions in solutionconcentration of ions in solution.
Ionic strength is dependent on the number of ions in solution and their charge. Not dependent on the chemical nature of the
ions
Ionic strength () = ½ (c1z12+ c2z2
2 + …)Or Ionic strength (m) = ½ cizi
2
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Examples Calculate the ionic strength of (a) 0.1 M
solution of KNO3 and (b) a 0.1 M solution of
Na2SO4 (c) a mixture containing 0.1 M KNO3
and 0.1 M Na2SO4.() = ½ (c1z1
2+ c2z22 + …)
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Alright, that’s great but how does it affect the equilibrium constant?
A + B C + D
Activity = Ac = [C]c
AND
bB
baA
a
dD
dcC
c
bB
aA
dD
cC
BA
DC
AA
AAK
][][
][][
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Relationship between activity coefficient and ionic strength
x
x
xz
3.31
51.0log
2
Debye-Huckel Equation
2 comments
= ionic strength of solution = activity coefficientZ = Charge on the species x = effective diameter of ion (nm)
(1)What happens to when approaches zero?(2)Most singly charged ions have an effective radius of about 0.3 nm
We generally don’t need to calculate – values are tabulated
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Concept Test
List at least three properties of activity coefficients
• Dimensionless• Depends on size of the ions (ex. Hg2
2+ and IO3-)
• Depends on the Ionic Strength of the Solution (K+ & NO3
-)• Depends on the charge of the ions (ex. Hg2
2+ and IO3
-)• In dilute solutions, where ionic strength is minimal,
the activity coefficient -> 1, and has little effect on equilibrium constant
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Activity coefficients are Activity coefficients are related to the hydrated related to the hydrated radius of atoms in radius of atoms in moleculesmolecules
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Relationship between and
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Back to our original problem
223
22
2
3223
22
][][ IOHgIOHgsp IOHgAAK
Consider a saturated solution of Hg2(IO3)2 in ‘pure water’. Calculate the concentration of mercurous ions.
Hg2(IO3)2(s) Hg22+ + 2IO3
- Ksp=1.3x10-18
At low ionic strengths -> 1
11 11
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Back to our original problem
223
22
2
3223
22
][][ IOHgIOHgsp IOHgAAK
Consider a saturated solution of Hg2(IO3)2 in ‘pure water’. Calculate the concentration of mercurous ions.
Hg2(IO3)2(s) Hg22+ + 2IO3
- Ksp=1.3x10-18
In 0.1 M KNO3 - how much Hg22+ will be dissolved?
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Back to our original problem
223
22
2
3223
22
][][ IOHgIOHgsp IOHgAAK
Consider a saturated solution of Hg2(IO3)2 in 0.1 M KNO0.1 M KNO33.. Calculate the concentration of mercurous ions.
Hg2(IO3)2(s) Hg22+ + 2IO3
- Ksp=1.3x10-18 22
322
2
3322
775.0][355.0][ IOIOHgsp IOHgAAK
222 775.0]2[355.0][3
22
xxAAK IOHgsp
)4(213122.0103.1 318 xx x 65 101.1
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Consider a saturated solution of Hg2(IO3)2 Calculate the concentration of mercurous ions in: In Pure water = 6.9 x 106.9 x 10-7-7
in 0.1 M KNO0.1 M KNO33 = 1.1 = 1.155 x 10 x 10-6-6
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pH revisited
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Definition of pH
pH = -log AH
or pH = - log [H+] H
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pH of pure water
H2O (l) H+ (aq) + OH-
(aq)Kw =1.0 x 10-14
Kw = AH AOH
Kw = [H+] H [OH-] OH
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pH of pure water
H2O (l) H+ (aq) + OH-
(aq)Kw =1.0 x 10-14
Kw = AH AOH
Kw = [H+] H [OH-] OH
Kw = x2 x = 1.0 x 10-7 M
11
- -ICE
+x +x+x +x
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pH of pure water
x = 1.0 x 10-7 M
Therefore [H+] = 1.0 x 10-7 M
pH = -log AH
= -log [H+] H
= - log [1.0 x 10-7]
= 7.00
1
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pH of pure water containing salt
Calculate the pH of pure water containing 0.10 M KCl at 25oC.
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