CTH :00-11:15 am Instructor: Dr. Upali Siriwardane Office: 311 Carson Taylor Hall ; Phone: ; 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, :30- 10:45 AM, CTH 311. Chemistry 281(01) Winter 2014

CHEM 281 Winter Definition? a) Arrhenius b) Bronsted-Lowry c) Lewis What are Acids &Bases?

CHEM 281 Winter Acid AcidAnything that produces hydrogen ions in a water solution. HCl (aq) H + + Cl - Base BaseAnything 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) Arrhenius definitions

Expands the Arrhenius definitions Acid AcidProton donor Base BaseProton acceptor This definition explains how substances like ammonia can act as bases. Eg. HCl(g) + NH 3 (g) > NH 4 Cl(s) HCl (acid), NH 3 (base). NH 3 (g) + H 2 O (l) NH OH - Brønsted-Lowry definitions Chapter 4-4CHEM 281 Winter 2014

Proton in water Chapter 4-5CHEM 281 Winter 2014

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 OH - (aq) Chapter 4-6CHEM 281 Winter 2014

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 Chapter 4-7 CHEM 281 Winter 2014

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. Examples.AcidBase 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- Brønsted-Lowry definitions Chapter 4-8CHEM 281 Winter 2014

Select acid, base, acid/conjugate base pair, base/conjugate acid pair H 2 SO 4 (aq) + H 2 O(l) H 3 + O(aq) + HSO 4 - (aq) acid base conjugate acid conjugate base base/conjugate acid pair acid/conjugate base pair Chapter 4-9CHEM 281 Winter 2014

Types of Acids and Bases Binary acids Oxyacid Organic acids Acidic oxides Basic oxides Amine Polyprotic acids Chapter 4-10CHEM 281 Winter 2014

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 Chapter 4-11CHEM 281 Winter 2014

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 Chapter 4-12CHEM 281 Winter 2014

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 Chapter 4-13CHEM 281 Winter 2014

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 Chapter 4-14CHEM 281 Winter 2014

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 Chapter 4-15CHEM 281 Winter 2014

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. Chapter 4-16CHEM 281 Winter 2014

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. Chapter 4-17CHEM 281 Winter 2014

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) Chapter 4-18CHEM 281 Winter 2014

Common acids and bases Acids Acids Formula Molarity* nitricHNO 3 16 hydrochloric HCl 12 sulfuricH 2 SO 4 18 aceticHC 2 H 3 O 2 18Bases ammoniaNH 3 (aq) 15 sodium hydroxideNaOH solid *undiluted. Chapter 4-19CHEM 281 Winter 2014

Acids and bases AcidicBasic Acidic Basic – Citrus fruitsBaking soda – Aspirin Detergents – Coca Cola Ammonia cleaners – VinegarTums and Rolaids – Vitamin CSoap Chapter 4-20CHEM 281 Winter 2014

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] Chapter 4-21CHEM 281 Winter 2014

What is K a HCl(aq) + H 2 O(l) H 3 + O(aq) + Cl - (aq) Chapter 4-22CHEM 281 Winter 2014

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] Chapter 4-23CHEM 281 Winter 2014

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) Chapter 4-24CHEM 281 Winter 2014

What is K b NH 3 (aq) + H 2 O(l) NH OH - (aq) Chapter 4-25CHEM 281 Winter 2014

H 2 SO 4 Dissociation E.g. 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 ) [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 - ] Chapter 4-26CHEM 281 Winter 2014

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 OH - (aq) [NH 4 + ][OH - ] NH 3 ; K b = [ NH 3 ] Chapter 4-27CHEM 281 Winter 2014

Acidity/Basicity of HA and F - Chapter 4-28CHEM 281 Winter 2014

Which is weaker? a. HNO 2 ; K a = 4.0 x b. HOCl 2 ; K a = 1.2 x c. HOCl ; K a = 3.5 x d. HCN ; K a = 4.9 x 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. Chapter 4-30

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 - ] = 1.0 x at 25 o C Note: Note: [H 2 O] is constant and is included in K w. ion product of water ion product of water Autoionization of water 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 Chapter 4-32CHEM 281 Winter 2014

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) Chapter 4-33CHEM 281 Winter 2014

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. Chapter 4-34CHEM 281 Winter 2014

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 pH and other “p” scales Chapter 4-35CHEM 281 Winter 2014

A logarithmic scale used to keep track of the large changes in [H + ] M 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. pH scale Chapter 4-36CHEM 281 Winter 2014

Substance pH 1 M HCl0.0 Gastric juices Lemon juice Classic Coke2.5 Coffee5.0 Pure Water7.0 Blood Milk of Magnesia 10.5 Household ammonia M NaOH 14.0 Substance pH 1 M HCl0.0 Gastric juices Lemon juice Classic Coke2.5 Coffee5.0 Pure Water7.0 Blood Milk of Magnesia 10.5 Household ammonia M NaOH 14.0 pH of some common materials Chapter 4-37CHEM 281 Winter 2014

What is pH? K w = [H 3 + O][OH - ] = 1 x [H 3 + O][OH - ] = x Extreme cases: Basic medium [H 3 + O][OH - ] = x 10 0 Acidic medium [H 3 + O][OH - ] = 10 0 x pH value is -log[H + ] spans only 0-14 in water. Chapter 4-38CHEM 281 Winter 2014

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 = pH + pOH pH = 14 - pOH pOH = 14 - pH Chapter 4-39CHEM 281 Winter 2014

Acid and Base Strength Strong acidsStrong acids Ionize completely in water. HCl, HBr, HI, HClO 3, HNO 3, HClO 4, H 2 SO 4. Weak acidsWeak acids Partially ionize in water. Most acids are weak. Strong basesStrong bases Ionize completely in water. Strong bases are metal hydroxides - NaOH, KOH Weak basesWeak bases Partially ionize in water. Chapter 4-40CHEM 281 Winter 2014

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 Chapter 4-41CHEM 281 Winter 2014

Titration curves pH Equivalence Point % titration or ml titrant Buffer region Overtitration Indicator Transition Chapter 4-42CHEM 281 Winter 2014

Indicators Acid-base indicators are highly colored weak acids or bases. HIn In - + H + color 1color 2 color 1 color 2 They may have more than one color transition. Example. Example. Thymol blue Red - Yellow - Blue One of the forms may be colorless - phenolphthalein (colorless to pink) Chapter 4-43CHEM 281 Winter 2014

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 Chapter 4-44CHEM 281 Winter 2014

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) Chapter 4-45CHEM 281 Winter 2014

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 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. Buffers Chapter 4-46CHEM 281 Winter 2014

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 pH = 14 - ( pK b + log ) [HA] [A - ] [HA] Buffers Chapter 4-47CHEM 281 Winter 2014

Control of blood pHControl of blood pH 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 OH 2 CO 3 (aq) H + (aq) + HCO 3 - (aq) The bicarbonate buffer is essential for controlling blood pH The bicarbonate buffer is essential for controlling blood pH Buffers and blood Chapter 4-48CHEM 281 Winter 2014

Main Group Acid/Bases Chapter 4-49CHEM 281 Winter 2014

Amphoteric Oxides Chapter 4-50CHEM 281 Winter 2014

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. Chapter 4-51CHEM 281 Winter 2014

pK a Values of Oxy Acids Chapter 4-52CHEM 281 Winter 2014

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) Chapter 4-53CHEM 281 Winter 2014

Lewis Acids/Bases Chapter 4-54CHEM 281 Winter 2014

Hard and soft acids and bases Chapter 4-55CHEM 281 Winter 2014

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) Chapter 4-56CHEM 281 Winter 2014

Acid-Base Discrimination Windows Chapter 4-57CHEM 281 Winter 2014

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 NH 3 NH NH HNO 3 H 2 NO NO 2 - 3HF H 2 F + + HF 2 - 2H 2 SO 4 H 3 SO HSO 4 - Chapter 4-58CHEM 281 Winter 2014

Polycation Formation NaAl 13 O 4 (OH) 24 (H 2 O) 12 (SO 4 ) 4.x H 2 O Chapter 4-59CHEM 281 Winter 2014

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 Chapter 4-60CHEM 281 Winter 2014