chemistry 281(01) winter 2014
DESCRIPTION
Chemistry 281(01) Winter 2014. CTH 277 10:00-11:15 am Instructor: Dr. Upali Siriwardane E-mail : [email protected] Office: 311 Carson Taylor Hall ; Phone: 318-257-4941; Office Hours: MTW 8:00 am - 10:00 am; TR 8:30 - 9:30 am & 1:00-2:00 pm. - PowerPoint PPT PresentationTRANSCRIPT
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CTH 277 10:00-11:15 amInstructor: Dr. Upali SiriwardaneE-mail: [email protected] Office: 311 Carson Taylor Hall ; Phone: 318-257-4941;Office Hours: MTW 8:00 am - 10:00 am; TR 8:30 - 9:30 am & 1:00-2:00 pm.January 16, 2014 Test 1 (Chapters 1&,2), February 6, 2014 Test 2 (Chapters 3 &4)February 25, 2014, Test 3 (Chapters 4 & 5),Comprehensive Final Make Up Exam: February 27, 2012 9:30-10:45 AM, CTH 311.
Chemistry 281(01) Winter 2014
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2CHEM 281 Winter 2014
Definition?
a) Arrhenius
b) Bronsted-Lowry
c) Lewis
What are Acids &Bases?
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3CHEM 281 Winter 2014
Acid Anything that produces hydrogen ions in a water solution.
HCl (aq) H+ + Cl-
Base Anything that produces hydroxideions in a water solution.
NaOH (aq) Na+ + OH-
Arrhenius definitions are limited to aqueous solutions.
Acid base reactions: HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)
Arrhenius definitions
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Expands the Arrhenius definitions
Acid Proton donorBase Proton acceptorThis definition explains how substances like
ammonia can act as bases.
Eg. HCl(g) + NH3(g) ------> NH4Cl(s) HCl (acid), NH3 (base).
NH3(g) + H2O(l) NH4+ + OH-
Brønsted-Lowry definitions
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Proton in water
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Dissociation EquilibriumHCl(aq) + H2O(l) H3
+O(aq) + Cl-(aq)
H2SO4(aq) + H2O(l) H3+O(aq) + HSO4
-(aq)
H2O(l) + H2O(l) H3+O(aq) + OH-(aq)
This dissociation is called autoionization of water.
HC2H3O2(aq) + H2O(l) H3+O(aq) + C2H3O2
-(aq)
NH3 (aq) + H2O(l) NH4+ + OH-(aq)
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Bronsted conjugate acid/base pairs in equilibria
HCl(aq) + H2O(l) H3+O(aq) + Cl-(aq)
HCl(aq): acidH2O(l): baseH3
+O(aq): conjugate acidCl-(aq): conjugate baseH2O/ H3
+O: base/conjugate acid pairHCl/Cl-: acid/conjugate base pair
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Conjugate acid-base pairs. Acids and bases that are related by loss or gain of H+ as H3O+ and H2O.Examples. Acid Base
H3O+ H2O
HC2H3O2 C2H3O2-
NH4+ NH3
H2SO4 HSO4-
HSO4-SO42-
Brønsted-Lowry definitions
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Select acid, base, acid/conjugate base pair,base/conjugate acid pair
H2SO4(aq) + H2O(l) H 3+O(aq) + HSO4
-(aq)acidbaseconjugate acidconjugate basebase/conjugate acid pairacid/conjugate base pair
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Types of Acids and Bases
Binary acids Oxyacid Organic acids Acidic oxidesBasic oxides AminePolyprotic acids
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Binary AcidsCompounds containing acidic protons
bonded to a more electronegative atom.
e.g. HF, HCl, HBr, HI, H2SThe acidity of the haloacid (HX; X = Cl, Br, I, F)Series increase in the following order: HF < HCl < HBr < HI
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OxyacidsCompounds containing acidic - OH
groups in the molecule.Acidity of H2SO4 is greater than H2SO3
because of the extra O (oxygens) The order of acidity of oxyacids from
the a halogen (Cl, Br, or I) shows a similar trend.
HClO4 > HClO3 > HClO2 >HClOperchloric chloric chlorus hyphochlorus
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Aqua Acids
Acidic proton is on a water molecule coordinated to a central metal ion
[Fe(OH2)6]3+,Al(OH2)63+, Si(OH)4
Acidity increase with charge
Acidity increase as metal become smaller
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Anhydrous oxides The Lux/Flood Definition
Covers things which would become acids or bases if dissolved in water.
Acidic Oxides These are usually oxides of non-metallic
elements such as P, S and N. E.g. NO2, SO2, SO3, CO2 They produce oxyacids when dissolved
in water
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Basic OxidesOxides oxides of metallic elements
such as Na, K, Ca. They produce hydroxyl bases when dissolved in water.
e.g. CaO + H2O --> Ca(OH)2
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Protic Acids
Monoprotic Acids: The form protic refers to acidity or protons. Monoprotic acids have only one acidic proton. e.g. HCl.
Polyprotic Acids: They have more than one acidic proton.
e.g. H2SO4 - diprotic acidH3PO4 - triprotic acid.
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AminesClass of organic bases derived
from ammonia NH3 by replacing hydrogen by organic groups. They are defined as bases similar to NH3 by Bronsted or Lewis acid/base definitions.
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What acid base concepts (Arrhenius/Bronsted/Lewis) would best describe the following reactions:
a) HCl(aq) + NaOH(aq) ---> NaCl(aq) + H2O(l)
b)HCl(g) + NH3(g) ---> NH4Cl(s)
c)BF3(g) + NH3(g) ---> F3B:NH3(s)
d)Zn(OH)2(s) + 2OH-(aq) ---> [Zn(OH)4]2- (aq)
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Common acids and bases
Acids Formula Molarity*nitric HNO3 16
hydrochloric HCl 12sulfuric H2SO4 18acetic HC2H3O2 18Basesammonia NH3(aq) 15sodium hydroxide NaOH solid
*undiluted.
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Acids and bases
Acidic Basic
– Citrus fruits Baking soda– Aspirin Detergents– Coca Cola Ammonia cleaners– Vinegar Tums and Rolaids– Vitamin C Soap
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Equilibrium, Constant, Ka & Kb
Ka: Acid dissociation constant for a equilibrium reaction. Kb: Base dissociation constant for a equilibrium reaction. Acid: HA + H2O H3
+O + A- Base: BOH + H2O B+ + OH-
[H3+O][ A-] [B+ ][OH-]
Ka = --------------- ; Kb = ----------------- [HA] [BOH]
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What is Ka
HCl(aq) + H2O(l) <===> H3+O(aq) + Cl-(aq)
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E.g. Ka
HCl(aq) + H2O(l) H3+O(aq) + Cl-(aq)
[H3+O][Cl-]
Ka= ----------------- [HCl]
[H+][Cl-] Ka= ----------------- [HCl]
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What is Ka1 and Ka2?
H2SO4(aq) + H2O(l) H3+O(aq) + HSO4
-(aq)
HSO4-(aq) + H2O(l) H3
+O(aq) + SO42-(aq)
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What is Kb
NH3 (aq) + H2O(l) NH4+ + OH-(aq)
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H2SO4 Dissociation
E.g.H2SO4(aq) + H2O(l) H3
+O(aq) + HSO4-(aq)
HSO4-(aq) + H2O(l) H3
+O(aq) + SO42-(aq)
[H3+O][HSO4
-] H2SO4 ; Ka1 = ------------------- [H2SO4] [H3
+O][SO42-]
H2SO4 ; Ka2 = ------------------- [HSO4
-]
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Ka and Kb
E.g.HC2H3O2(aq) + H2O(l) H3
+O(aq) + C2H3O2-(aq)
[H+][C2H3O2-]
H C2H3O2; Ka= ------------------ [H C2H3O2]
NH3 (aq) + H2O(l) NH4+ + OH-(aq)
[NH4+][OH-]
NH3; Kb= -------------- [ NH3]
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Acidity/Basicity of HA and F-
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Which is weaker?
• a. HNO2 ; Ka= 4.0 x 10-4.• b. HOCl2 ; Ka= 1.2 x 10-2.• c. HOCl ; Ka= 3.5 x 10-8.• d. HCN ; Ka= 4.9 x 10-10.
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WEAKER/STRONGER Acids and Bases & Ka and Kb
values
• A larger value of Ka or Kb indicates an equilibrium favoring product side.
• Acidity and basicity increase with increasing Ka or Kb.
• pKa = - log Ka and pKb = - log Kb
• Acidity and basicity decrease with increasing pKa or pKb.
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Autoionization When water molecules react with one another to form ions.
H2O(l) + H2O(l) H3O+(aq) + OH-
(aq)
(10-7M) (10-7M)
Kw = [ H3O+ ] [ OH- ]
= 1.0 x 10-14 at 25oC Note: [H2O] is constant and is included in Kw.
ion productof water
Autoionization of water
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What is Kw?H2O(l) + H2O(l) H3
+O(aq) + OH-(aq) This dissociation is called autoionization of
water. Autoionization of water: Kw = [H3
+O][OH-]Kw is called ionic product of waterKw = 1 x 10-14
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Why is water important for acid/base equilibria?
Water is the medium/solvent for acids and bases.
Acids and bases alter the dissociation equilibrium of water based on Le Chaterlier’s principle
H2O(l) + H2O(l) H3+O(aq) + OH-(aq)
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Comparing Kw and Ka & Kb
Any compound with a Ka value greater than Kw of water will be a an acid in water.
Any compound with a Kb value greater than Kw of water will be a base in water.
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We need to measure and use acids and bases over a very large concentration range.
pH and pOH are systems to keep track of these very large ranges.– pH = -log[H3O+]– pOH = -log[OH-]– pH + pOH = 14
pH and other “p” scales
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A logarithmic scale used to keep track of the large changes in [H+].
14 7 010-14 M 10-7 M 1 M Very Neutral VeryBasic Acidic
When you add an acid, the pH gets smaller.When you add a base, the pH gets larger.
pH scale
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Substance pH
1 M HCl 0.0Gastric juices 1.0 - 3.0Lemon juice 2.2 - 2.4Classic Coke 2.5Coffee 5.0Pure Water 7.0Blood 7.35 - 7.45Milk of Magnesia 10.5Household ammonia 12.01M NaOH 14.0
pH of some common materials
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What is pH?
Kw = [H3+O][OH-] = 1 x 10-14
[H3+O][OH-] = 10-7 x 10-7
Extreme cases:Basic medium [H3
+O][OH-] = 10-14 x 100 Acidic medium [H3
+O][OH-] = 100 x 10-14 pH value is -log[H+]spans only 0-14 in water.
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pH, pKw and pOHThe relation of pH, Kw and pOH Kw = [H+][OH-] log Kw = log [H+] + log [OH-] -log Kw= -log [H+] -log [OH-] ; previous equation multiplied by -1 pKw = pH + pOH; pKw = 14 since Kw =1 x 10-14
14 = pH + pOH pH = 14 - pOH pOH = 14 - pH
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Acid and Base Strength• Strong acids Ionize completely in water.
HCl, HBr, HI, HClO3, HNO3, HClO4, H2SO4.
• Weak acids Partially ionize in water. Most acids are weak.
• Strong bases Ionize completely in water. Strong bases are metal
hydroxides - NaOH, KOH• Weak bases Partially ionize in water.
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pH and pOH calculations of acid and base solutions
a) Strong acids/bases dissociation is complete for strong acid
such as HNO3 or base NaOH
[H+] is calculated from molarity (M) of the solution
b) weak acids/bases needs Ka , Kb or percent(%)dissociation
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Titration curvespH Equivalence
Point
% titration or ml titrant
Buffer region
OvertitrationIndicatorTransition
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IndicatorsAcid-base indicators are highly colored weak
acids or bases. HIn In- + H+
color 1 color 2
They may have more than one color transition. Example. Thymol blue
Red - Yellow - Blue One of the forms may be colorless -
phenolphthalein (colorless to pink)Chapter 4-43CHEM 281 Winter 2014
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Selection of an indicator for a titration
a) strong acid/strong base b) weak acid/strong base c) strong acid/weak base d) weak acid/weak base Calculate the pH of the solution at he
equivalence point or end point
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Common Ion Effect
Weak acid and salt solutionsE.g. HC2H3O2 and NaC2H3O2
Weak base and salt solutionsE.g. NH3 and NH4Cl. H2O + C2H3O2
- <==> OH- + HC2H3O2 (common ion)
H2O + NH4+ <==> H3
+O + NH3 (common ion)
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Solutions that resist pH change when small amounts of acid or base are added.
Two typesweak acid and its saltweak base and its salt
HA(aq) + H2O(l) H3O+(aq) + A-(aq)
Add OH- Add H3O+
shift to right shift to left Based on the common ion effect.
Buffers
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The pH of a buffer does not depend on the absolute amount of the conjugate acid-base pair. It is based on the ratio of the two.Henderson-Hasselbalch equation.Easily derived from the Ka or Kb expression.
Starting with an acid
pH = pKa + log Starting with a base
pH = 14 - ( pKb + log )[HA][A-]
[A-][HA]
Buffers
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• Control of blood pH
Oxygen is transported primarily by hemoglobin in the red blood cells.
CO2 is transported both in plasma and the red blood cells.CO2 (aq) + H2O H2CO3 (aq)
H+(aq) + HCO3-(aq)
The bicarbonatebuffer is essential
for controllingblood pH
Buffers and blood
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Main Group Acid/Bases
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Amphoteric Oxides
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Strength of oxo-acids by Paulings Rules
For OpE(OH)q, pKa ~ 8 - 5pThe successive pKa values of polyprotic acids (i.e.
q >1) increase by 5 units for each successive proton transfer.
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pKa Values of Oxy Acids
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Lewis Definition
• Lewis was successful in including acid and bases without proton or hydroxyl ions.
• Lewis Acid: A substance that accepts an electron pair.
• Lewis base: A substance that donates an electron pair.
• E.g. BF3(g) + :NH3(g) F3B:NH3(s)
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Lewis Acids/Bases
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Hard and soft acids and bases
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Solvent leveling
• If the solvent contains ionizable protons it is said to be protonic, and if it is protonic, it will engage in acid-base reactions.
• All acids/bases which are stronger than the H3O+(aq) or OH-(aq) ion will react to produce hydronium/hydroxide ion, and so their strength will be leveled to that of the H3O+(aq) or OH-(aq) ion.
• In aqueous solution, the strongest acid/base which can exist is the H3O+(aq) or OH-(aq)
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Acid-Base Discrimination Windows
Chapter 4-57CHEM 281 Winter 2014
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Levelling effect in other protic liquid
all acids are levelled to the strength of theammonium ion, NH4
+, and all bases are levelled to the strength of the amide ion, NH2
-. 2 NH3 NH4
+ + NH2-.
2HNO3 H2NO3+ + NO2
-
3HF H2F+ + HF2-
2H2SO4 H3SO4+ + HSO4
-
Chapter 4-58CHEM 281 Winter 2014
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Polycation Formation
NaAl13O4(OH)24(H2O)12(SO4)4 .x H2O
Chapter 4-59CHEM 281 Winter 2014
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Polyanion Formation:ZeolitesThe general method of zeolite production involves dissolving an aluminium source (metal or oxide) into an aqueous solution of sodium or potassium hydroxide. Once this solution has cooled the silica source (and organic template, if required) is added in The form of an aqueous slurry and the resulting gel stirred until homogenous.Na12[(AlO2)12(SiO2)12.27H2O
Chapter 4-60CHEM 281 Winter 2014