Equilibrium Constant Determination eral Solubilities of Common Compounds in Wa Guidelines for Identifying Electrolytes and Non-electrolytes Guidelines for Writing Net Ionic Equations Ionization Constants for Acids and Bases Problem Set Handouts
Dec 22, 2015
Equilibrium Constant Determination
General Solubilities of Common Compounds in Water
Guidelines for IdentifyingElectrolytes and Non-electrolytes
Guidelines for Writing Net Ionic Equations
Ionization Constants for Acids and Bases
Problem Set
Handouts
Aqueous EquilibriaElectrolytic Character
Edward A. Mottel
Department of Chemistry
Rose-Hulman Institute of Technology
04/19/23
Electrolytes
• Reading Assignment: • Chang: Chapter 14.5; Lab manual Exp. F
• The degree that a compound dissociates into ions is a measure of its strength, not its concentration.• Strong electrolytes - dissociate virtually
100% into ions, at all concentrations• Weak electrolytes - dissociate less than
50% into ions• Non-electrolytes - do not form ions when
dissolved in a solvent.
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Strong Electrolytes
• Strong Acids
• HCl, HBr, HI, HNO3, H2SO4, HClO4, etc.
• Strong Bases• Group IA hydroxides: NaOH, KOH
• Ca(OH)2, Sr(OH)2, Ba(OH)2
• Most ionic compounds
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Strong Electrolytes
• Soluble Salts• Binary compounds of metal cations with
nonmetal anions• Compounds of metal cations with
polyatomic anions• Ammonium cation with nonmetal or
polyatomic anions.
Which of these are soluble, strong electrolytes?
KCl, Zn(NO3)2, CuSO4, NH4I
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Strong Electrolytes
• Slightly soluble salts• Compounds which have a solubility
product constant (Ksp) are strong electrolytes, but are not very soluble.
• AgCl, BaSO4, Mg(OH)2, etc.
This indicates that AgClisn’t very soluble.(sparingly soluble)
AgCl (s) AgCl (aq) Ag+(aq) + Cl–(aq)
This indicates that theamount of AgCl which dissolves
ionizes extensively.(strong electrolyte)
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Weak Electrolytes
• Weak acids, weak bases, and other soluble compounds which do not ionize extensively.
• A weak electrolyte will usually have a dissociation constant associated with it such as Ka or Kb.
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Weak Electrolytes
• Weak Acids
• HCOOH, CH3COOH, HF, HCN, HNO2, H3PO4, H2S, HS–, H2CO3, HCO3
–, etc.
• Weak Bases
• NH3, CH3NH2, N2H4, etc.
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Non-electrolytes
Compounds which dissolve but do not form a significant number of ions.
Most covalent compounds: compounds of two or more nonmetals excluding those which are strong or weak electrolytes.• water, sugar, methanol, ethylene glycol,
etc.
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Solubility is related to theconcentration of the solute
in the solvent
Dissociationis related
to the ability ofthe compoundto form ionsin solution
Categorize each of thefollowing compounds
in terms of its solubilityand tendency to form ions.
oilNaClsugar
acetic acidCa(OH)2
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Electrolytic Character SolubilityExamples
• Oil -- not very soluble, doesn’t ionize• NaCl -- very soluble and very conductive• Sugar -- very soluble but non-conducting• Acetic acid -- very soluble but poorly
conducting• Calcium hydroxide -- slightly soluble but
the amount that dissolves, completely ionizes in water
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Solubility is related to theconcentration of the solute
in the solvent
Dissociationis related
to the ability ofthe compoundto form ionsin solution
solubleslightlysoluble
strong
weak
non-electrolyte
oil
NaCl Ca(OH)2
sugar
acetic acid CO2
The solubility of a compound does not predictits electrolytic character.
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Equation Notation
Each compound in solution is considered in its “predominant” form with proper annotation:
HCl(aq) H+(aq) + Cl– (aq)
KOH (aq) K+(aq) + OH– (aq)
• Strong Electrolytes as completely dissociated.
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Equation Notation
Each compound in solution is considered in its “predominant” form with proper annotation:• Weak Electrolytes and Non-electrolytes as
molecular compounds
HF(aq) H+(aq) + F– (aq)
CH3OH (aq) H+(aq) + CH3O–
(aq)
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Group Activity
Identify the predominant form and write a dissociation reaction for the following compounds• nitric acid• hydrofluoric acid• potassium chlorate• aqueous ammonia• sodium hydroxide
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Equilibrium Arrows
HNO3(aq) H+(aq) + NO3–
(aq)
HF(aq) H+(aq) + F– (aq)
KClO3(aq) K+(aq) + ClO3–
(aq)
NH3(aq) + H2O (l) NH4+(aq) + OH–
(aq)
NaOH (aq) Na+(aq) + OH– (aq)
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Ionization Constants
Acid dissociation constants, Ka
• The larger the constant, the stronger the acid.
Base dissociation constants, Kb
• The larger the constant, the stronger the base.
Function of temperature
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Acid Strength
acetic acidphosphoric acidnitrous acid
Rank the following compounds in terms of acid strength (strongest to weakest).
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Acid Strength
H3PO4 7.5 x 10–3
Rank the following compounds in terms of acid strength (strongest to weakest).
HNO2 4.5 x 10–4
CH3COOH 1.8 x
10–5
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Numeric Values of
Ionization Constants
Describe this reaction in a sentence.
F–(aq) + H+(aq) HF(aq)
How is the equation listed in the Ionization Constants of Aqueous Acids table?
What is the numerical value of the reaction? Is the arrow notation correct?
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Numeric Values of
Ionization Constants
F–(aq) + H+(aq) HF(aq)
HF(aq) H+(aq) + F–(aq) Ka= 7.2 x 10–4 M
K = 1 / 7.2 x 10–4 M–1
= 1.4 x 103 M–1
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Numeric Values of
Equilibrium Constants
For carbonic acid• write the acid dissociation reaction.• determine the mass-action expression.• find the numeric value of the equilibrium
constant.• confirm the equilibrium arrow assignment.
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Carbonic Acid
H2CO3(aq) H+(aq) + HCO3–(aq) Ka,1= 4.2 x 10–7
HCO3–
(aq) H+(aq) + CO32–(aq) Ka,2= 4.8 x 10–11
Write the mass-action expression forthe second ionization of carbonic acid.
Carbonic acid has more than one acidic proton, and each ionization has its own
constant.
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Determining Unlisted
Equilibrium Constants
H2CO3(aq) 2 H+(aq) + CO32–(aq)
What is the numeric value of theequilibrium constant for this reaction?
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Determining Unlisted
Equilibrium Constants
[H+]2 [CO32–]
[H2CO3][H+] [HCO3
–]
[H2CO3]= 4.2 x 10–7
[H+] [CO32–]
[HCO3–]
= 4.8 x 10–11
What is similar, what is different?
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Determining Unlisted
Equilibrium Constants
[H+]2 [CO32–]
[H2CO3]=
[H+] [HCO3–]
[H2CO3]
[H+] [CO32–]
[HCO3–]
= 4.2 x 10–7 4.8 x 10–11
= 2.0 x 10–17 M2
H2CO3(aq) 2 H+(aq) + CO32–(aq)
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Chemical EquationsCan Be Treated Algebraically
H2CO3(aq) H+ (aq) + HCO3
– (aq)
HCO3–
(aq) H+ (aq) + CO3
2– (aq)
H2CO3(aq) 2 H+ (aq) + CO3
2– (aq)
target equation
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Numeric Values of
Dissociation Constants
Describe the reaction in a sentence. How is the listed Kb equation related to this
reaction?
NH4+(aq) NH3(aq) + H+(aq)
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Dissociation of Ammonium Ion
NH4+(aq) NH3(aq) + H+(aq) (target)
NH4+(aq) + OH–(aq) NH3 (aq) + H2O(l)
What other equation can be added to the first equationto give the target equation?
H2O(l) OH–(aq) + H+(aq)
What is the numeric value of the equilibrium constant?
Assignments
Equilibrium Constant Determination Problem Set
Complete Experiment F in the laboratory manual
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Group Activity
hydrogen peroxide
water
ammonium ion
Rank the following species in terms of acid strength (strongest to weakest).
ammonium ion
hydrogen peroxide
water