Chemistry 281(01) Winter 2014 CTH 277 10:00-11:15 am Instructor: Dr. Upali Siriwardane E-mail: upali@latech.edu 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.
What are Acids &Bases? Definition? a) Arrhenius b) Bronsted-Lowry c) Lewis CHEM 281 Winter 2009 Chapter 4-2
Arrhenius definitions Acid Anything that produces hydrogen ions in a water solution. HCl (aq) H + + Cl - Base Anything that produces hydroxide ions in a water solution. NaOH (aq) Na + + OH - Arrhenius definitions are limited to aqueous solutions. Acid base reactions: HCl(aq) + NaOH(aq) NaCl(aq) + H 2 O(l) CHEM 281 Winter 2009 Chapter 4-3
Brønsted-Lowry definitions Expands the Arrhenius definitions Acid Proton donor Base Proton acceptor This definition explains how substances like ammonia can act as bases. NH 3 (g) + H 2 O(l) NH 4 + + OH - Eg. HCl(g) + NH 3 (g) ------> NH 4 Cl(s) HCl (acid), NH 3 (base). CHEM 281 Winter 2009 Chapter 4-4
Proton in water CHEM 281 Winter 2009 Chapter 4-5
Dissociation Equilibrium HCl(aq) + H 2 O(l) H 3+ O(aq) + Cl - (aq) H 2 SO 4 (aq) + H 2 O(l) H 3+ O(aq) + HSO 4- (aq) H 2 O(l) + H 2 O(l) H 3+ O(aq) + OH - (aq) This dissociation is called autoionization of water. HC 2 H 3 O 2 (aq) + H 2 O(l) H 3+ O(aq) + C 2 H 3 O 2- (aq) NH 3 (aq) + H 2 O(l) NH 4 + + OH - (aq) CHEM 281 Winter 2009 Chapter 4-6
Bronsted conjugate acid/base pairs in equilibria HCl(aq) + H 2 O(l) H 3+ O(aq) + Cl - (aq) HCl(aq): acid H 2 O(l): base H 3+ O(aq): conjugate acid Cl - (aq): conjugate base H 2 O/ H 3+ O: base/conjugate acid pair HCl/Cl - : acid/conjugate base pair CHEM 281 Winter 2009 Chapter 4-7
Brønsted-Lowry definitions Conjugate acid-base pairs. Acids and bases that are related by loss or gain of H + as H 3 O + and H 2 O. Examples. Acid Base H 3 O + H 2 O HC 2 H 3 O 2 C 2 H 3 O 2 - NH 4 + NH 3 H 2 SO 4 HSO 4 - HSO 4- SO 4 2- CHEM 281 Winter 2009 Chapter 4-8
Select acid, base, acid/conjugate base pair, base/conjugate acid pair H 2 SO 4 (aq) + H 2 O(l) acid base conjugate acid conjugate base base/conjugate acid pair acid/conjugate base pair H 3+ O(aq) + HSO 4- (aq) CHEM 281 Winter 2009 Chapter 4-9
Types of Acids and Bases Binary acids Oxyacid Organic acids Acidic oxides Basic oxides Amine Polyprotic acids CHEM 281 Winter 2009 Chapter 4-10
Binary Acids Compounds containing acidic protons bonded to a more electronegative atom. e.g. HF, HCl, HBr, HI, H 2 S The acidity of the haloacid (HX; X = Cl, Br, I, F) Series increase in the following order: HF < HCl < HBr < HI CHEM 281 Winter 2009 Chapter 4-11
Oxyacids Compounds containing acidic - OH groups in the molecule. Acidity of H 2 SO 4 is greater than H 2 SO 3 because of the extra O (oxygens) The order of acidity of oxyacids from the a halogen (Cl, Br, or I) shows a similar trend. HClO 4 > HClO 3 > HClO 2 >HClO perchloric chloric chlorus hyphochlorus CHEM 281 Winter 2009 Chapter 4-12
Aqua Acids Acidic proton is on a water molecule coordinated to a central metal ion [Fe(OH 2 ) 6 ] 3+,Al(OH 2 ) 6 3+, Si(OH) 4 Acidity increase with charge Acidity increase as metal become smaller CHEM 281 Winter 2009 Chapter 4-13
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. NO 2, SO 2, SO 3, CO 2 They produce oxyacids when dissolved in water CHEM 281 Winter 2009 Chapter 4-14
Basic Oxides Oxides oxides of metallic elements such as Na, K, Ca. They produce hydroxyl bases when dissolved in water. e.g. CaO + H 2 O --> Ca(OH) 2 CHEM 281 Winter 2009 Chapter 4-15
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. H 2 SO 4 - diprotic acid H 3 PO 4 - triprotic acid. CHEM 281 Winter 2009 Chapter 4-16
Amines Class of organic bases derived from ammonia NH 3 by replacing hydrogen by organic groups. They are defined as bases similar to NH 3 by Bronsted or Lewis acid/base definitions. CHEM 281 Winter 2009 Chapter 4-17
What acid base concepts (Arrhenius/Bronsted/Lewis) would best describe the following reactions: a) HCl(aq) + NaOH(aq) ---> NaCl(aq) + H 2 O(l) b)hcl(g) + NH 3 (g) ---> NH 4 Cl(s) c)bf 3 (g) + NH 3 (g) ---> F 3 B:NH 3 (s) d)zn(oh) 2 (s) + 2OH - (aq) ---> [Zn(OH) 4 ] 2- (aq) CHEM 281 Winter 2009 Chapter 4-18
Common acids and bases Acids Formula Molarity* nitric HNO 3 16 hydrochloric HCl 12 sulfuric H 2 SO 4 18 acetic HC 2 H 3 O 2 18 Bases ammonia NH 3 (aq) 15 sodium hydroxide NaOH solid *undiluted. CHEM 281 Winter 2009 Chapter 4-19
Acids and bases Acidic Basic Citrus fruits Baking soda Aspirin Detergents Coca Cola Ammonia cleaners Vinegar Tums and Rolaids Vitamin C Soap CHEM 281 Winter 2009 Chapter 4-20
Equilibrium, Constant, K a & K b K a : Acid dissociation constant for a equilibrium reaction. K b : Base dissociation constant for a equilibrium reaction. Acid: HA + H 2 O H 3+ O + A - Base: BOH + H 2 O B + + OH - [H 3+ O][ A - ] [B + ][OH - ] K a = --------------- ; K b = ----------------- [HA] [BOH] CHEM 281 Winter 2009 Chapter 4-21
What is K a HCl(aq) + H 2 O(l) <===> H 3+ O(aq) + Cl - (aq) CHEM 281 Winter 2009 Chapter 4-22
E.g. K a HCl(aq) + H 2 O(l) H 3+ O(aq) + Cl - (aq) [H 3+ O][Cl-] K a = ----------------- [HCl] [H + ][Cl-] K a = ----------------- [HCl] CHEM 281 Winter 2009 Chapter 4-23
What is K a1 and K a2? H 2 SO 4 (aq) + H 2 O(l) H 3+ O(aq) + HSO 4- (aq) HSO 4- (aq) + H 2 O(l) H 3+ O(aq) + SO 4 2- (aq) CHEM 281 Winter 2009 Chapter 4-24
What is K b NH 3 (aq) + H 2 O(l) NH 4 + + OH - (aq) CHEM 281 Winter 2009 Chapter 4-25
H 2 SO 4 Dissociation E.g. H 2 SO 4 (aq) + H 2 O(l) HSO 4- (aq) + H 2 O(l) H 3+ O(aq) + HSO 4- (aq) H 3+ O(aq) + SO 2-4 (aq) [H 3+ O][HSO 4- ] H 2 SO 4 ; K a1 = ------------------- [H 2 SO 4 ] [H 3+ O][SO 4 2- ] H 2 SO 4 ; K a2 = ------------------- [HSO 4- ] CHEM 281 Winter 2009 Chapter 4-26
K a and K b E.g. HC 2 H 3 O 2 (aq) + H 2 O(l) H 3+ O(aq) + C 2 H 3 O 2- (aq) [H + ][C 2 H 3 O 2- ] H C 2 H 3 O 2 ; K a = ------------------ [H C 2 H 3 O 2 ] NH 3 (aq) + H 2 O(l) [NH 4+ ][OH - ] NH 3 ; K b = -------------- [ NH 3 ] NH 4 + + OH - (aq) CHEM 281 Winter 2009 Chapter 4-27
Acidity/Basicity of HA and F - CHEM 281 Winter 2009 Chapter 4-28
Which is weaker? a. HNO 2 ; K a = 4.0 x 10-4. b. HOCl 2 ; K a = 1.2 x 10-2. c. HOCl ; K a = 3.5 x 10-8. d. HCN ; K a = 4.9 x 10-10. CHEM 281 Winter 2009 Chapter 4-29
WEAKER/STRONGER Acids and Bases & K a and K b values A larger value of K a or K b indicates an equilibrium favoring product side. Acidity and basicity increase with increasing K a or K b. pk a = - log K a and pk b = - log K b Acidity and basicity decrease with increasing pk a or pk b. CHEM 281 Winter 2009 Chapter 4-30
Autoionization of water Autoionization When water molecules react with one another to form ions. H 2 O (l) + H 2 O (l) H 3 O + (aq) + OH - (aq) (10-7 M) (10-7 M) K w = [ H 3 O + ] [ OH - ] ion product of water = 1.0 x 10-14 at 25 o C Note: [H 2 O] is constant and is included in K w. CHEM 281 Winter 2009 Chapter 4-31
What is K w? H 2 O(l) + H 2 O(l) H 3+ O(aq) + OH - (aq) This dissociation is called autoionization of water. Autoionization of water: K w = [H 3+ O][OH - ] K w is called ionic product of water K w = 1 x 10-14 CHEM 281 Winter 2009 Chapter 4-32
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 H 2 O(l) + H 2 O(l) H 3+ O(aq) + OH - (aq) CHEM 281 Winter 2009 Chapter 4-33
Comparing K w and K a & K b Any compound with a K a value greater than K w of water will be a an acid in water. Any compound with a K b value greater than K w of water will be a base in water. CHEM 281 Winter 2009 Chapter 4-34
ph and other p scales 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[h 3 O + ] poh = -log[oh - ] ph + poh = 14 CHEM 281 Winter 2009 Chapter 4-35
ph scale A logarithmic scale used to keep track of the large changes in [H + ]. 14 7 0 10-14 M 10-7 M 1 M Very Neutral Very Basic Acidic When you add an acid, the ph gets smaller. When you add a base, the ph gets larger. CHEM 281 Winter 2009 Chapter 4-36
ph of some common materials Substance ph 1 M HCl 0.0 Gastric juices 1.0-3.0 Lemon juice 2.2-2.4 Classic Coke 2.5 Coffee 5.0 Pure Water 7.0 Blood 7.35-7.45 Milk of Magnesia 10.5 Household ammonia 12.0 1M NaOH 14.0 CHEM 281 Winter 2009 Chapter 4-37
What is ph? K w = [H 3+ O][OH - ] = 1 x 10-14 [H 3+ O][OH - ] = 10-7 x 10-7 Extreme cases: Basic medium [H 3+ O][OH - ] = 10-14 x 10 0 Acidic medium [H 3+ O][OH - ] = 10 0 x 10-14 ph value is -log[h + ] spans only 0-14 in water. CHEM 281 Winter 2009 Chapter 4-38
ph, pk w and poh The relation of ph, K w and poh K w = [H + ][OH - ] log K w = log [H + ] + log [OH - ] -log K w = -log [H + ] -log [OH - ] ; previous equation multiplied by -1 pk w = ph + poh; pk w = 14 since K w =1 x 10-14 14 = ph + poh ph = 14 - poh poh = 14 - ph CHEM 281 Winter 2009 Chapter 4-39
Acid and Base Strength Strong acids Weak acids Ionize completely in water. HCl, HBr, HI, HClO 3, HNO 3, HClO 4, H 2 SO 4. 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. CHEM 281 Winter 2009 Chapter 4-40
ph and poh calculations of acid and base solutions a) Strong acids/bases dissociation is complete for strong acid such as HNO 3 or base NaOH [H + ] is calculated from molarity (M) of the solution b) weak acids/bases needs K a, K b or percent(%)dissociation CHEM 281 Winter 2009 Chapter 4-41
ph Titration curves Indicator Transition Overtitration Equivalence Point Buffer region % titration or ml titrant CHEM 281 Winter 2009 Chapter 4-42
Indicators Acid-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) CHEM 281 Winter 2009 Chapter 4-43
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 CHEM 281 Winter 2009 Chapter 4-44
Common Ion Effect Weak acid and salt solutions E.g. HC 2 H 3 O 2 and NaC 2 H 3 O 2 Weak base and salt solutions E.g. NH 3 and NH 4 Cl. H 2 O + C 2 H 3 O 2 - <==> OH - + HC 2 H 3 O 2 (common ion) H 2 O + NH 4 + <==> H 3+ O + NH 3 (common ion) CHEM 281 Winter 2009 Chapter 4-45
Solutions that resist ph change when small amounts of acid or base are added. Two types weak acid and its salt weak base and its salt Buffers HA(aq) + H 2 O(l) H 3 O + (aq) + A - (aq) Add OH - Add H 3 O + shift to right shift to left Based on the common ion effect. CHEM 281 Winter 2009 Chapter 4-46
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 K a or K b expression. Starting with an acid ph = pk a + log Starting with a base Buffers [A - ] [HA] [HA] [A - ] ph = 14 - ( pk b + log ) CHEM 281 Winter 2009 Chapter 4-47
Control of blood ph Buffers and blood Oxygen is transported primarily by hemoglobin in the red blood cells. CO 2 is transported both in plasma and the red blood cells. CO 2 (aq) + H 2 O H 2 CO 3 (aq) The bicarbonate buffer is essential for controlling blood ph H + (aq) + HCO 3 - (aq) CHEM 281 Winter 2009 Chapter 4-48
Main Group Acid/Bases CHEM 281 Winter 2009 Chapter 4-49
Amphoteric Oxides CHEM 281 Winter 2009 Chapter 4-50
Strength of oxo-acids by Paulings Rules For O p E(OH) q, pk a ~ 8-5p The successive pk a values of polyprotic acids (i.e. q >1) increase by 5 units for each successive proton transfer. CHEM 281 Winter 2009 Chapter 4-51
pk a Values of Oxy Acids CHEM 281 Winter 2009 Chapter 4-52
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. BF 3 (g) + :NH 3 (g) F 3 B:NH 3 (s) CHEM 281 Winter 2009 Chapter 4-53
Lewis Acids/Bases CHEM 281 Winter 2009 Chapter 4-54
Hard and soft acids and bases CHEM 281 Winter 2009 Chapter 4-55
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 H 3 O + (aq) or OH - (aq) ion will react to produce hydronium/hydroxide ion, and so their strength will be leveled to that of the H 3 O + (aq) or OH - (aq) ion. In aqueous solution, the strongest acid/base which can exist is the H 3 O + (aq) or OH - (aq) CHEM 281 Winter 2009 Chapter 4-56
Acid-Base Discrimination Windows CHEM 281 Winter 2009 Chapter 4-57
Levelling effect in other protic liquid all acids are levelled to the strength of the ammonium ion, NH 4+, and all bases are levelled to the strength of the amide ion, NH 2-. 2 NH 3 NH 4 + + NH 2-. 2HNO 3 H 2 NO 3 + + NO 2-3HF H 2 F + + HF 2-2H 2 SO 4 H 3 SO 4 + + HSO 4 - CHEM 281 Winter 2009 Chapter 4-58
Polycation Formation NaAl 13 O 4 (OH) 24 (H 2 O) 12 (SO 4 ) 4.x H 2 O CHEM 281 Winter 2009 Chapter 4-59
Polyanion Formation:Zeolites The 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. Na 12 [(AlO 2 )12(SiO 2 ) 12.27H 2 O CHEM 281 Winter 2009 Chapter 4-60