C. Y. Yeung (CHW, 2009) p.01 Acid-Base Eqm (2): K a and K b Review Questions Calculate the pH : Q.110 -8 HCl(aq) [100% ionized] Q.20.01M NaOH(aq) [100%

Slides:

Advertisements

Similar presentations

PART 4: Salt Hydrolysis and Buffer Solutions

Advertisements

Acids and Bases Section 18.1: Calculations involving Acids and Bases Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or.

Acid Base Equilibria Dr. Harris Ch 20 Suggested HW: Ch 20: 5, 9, 11*, 19*, 21, 29**, 35, 56** * Use rule of logs on slide 10 ** Use K a and K b tables.

ACIDS AND BASES Dissociation Constants. weaker the acid, the stronger its conjugate base stronger the acid, the weaker its conjugate base.

Acids and Bases Chapter and Br Ø nstead Acids and Br Ø nstead Bases Recall from chapter 4: Recall from chapter 4: –Br Ø nstead Acid-

Relationship Between Ka and Kb. Consider the dissociation of a weak acid: CH 3 COOH (aq) + H 2 O (l)  H 3 O + (aq) + CH 3 COO - (aq) K a = [H 3 O + ][CH.

Acid-Base Equilibria Chapter 16. HA (aq) + H 2 O (l) H 3 O + (aq) + A - (aq) Weak Acids (HA) and Acid Ionization Constants HA (aq) H + (aq) + A - (aq)

Acid-Base Equilibria Chapter 16.

PH = - log [H 3 O + ] [H 3 O + ] = 10 - pH mol/L For pure water at 25 o C pH = - log (1.0 x ) = 7.00 For a change in pH by 1, H 3 O + concentration.

Polyprotic Acids & Bases A polyprotic acid can donate more than one H + Carbonic acid: H 2 CO 3 (aq); dissolved CO 2 in water Sulfuric acid: H 2 SO 4 (aq)

EQUILIBRIUM Part 1 Common Ion Effect. COMMON ION EFFECT Whenever a weak electrolyte and a strong electrolyte share the same solution, the strong electrolyte.

Acids and Bases Chapter 20 Lesson 2. Definitions Acids – produce H + Bases - produce OH - Acids – donate H + Bases – accept H + Acids – accept e - pair.

Acids and Bases © 2009, Prentice-Hall, Inc. Chapter 16 Acids and Bases John D. Bookstaver St. Charles Community College Cottleville, MO Chemistry, The.

Chapter 16 Acid–Base Equilibria Lecture Presentation Dr. Subhash C Goel South GA State College Douglas, GA © 2012 Pearson Education, Inc.

Chapter 16 Acid–Base Equilibria

Chapter 16 Acids and Bases. © 2009, Prentice-Hall, Inc. Some Definitions Arrhenius – An acid is a substance that, when dissolved in water, increases the.

Calculations Involving Acids and Bases IB Chemistry Power Points Topic 18 Acids and Bases

Acids and Bases AP Chemistry Seneca Valley Chapter

Unless otherwise stated, all images in this file have been reproduced from: Blackman, Bottle, Schmid, Mocerino and Wille, Chemistry, 2007 (John Wiley)

The pK a Scale. Acid Dissociation Constant, K a K a, is a measure of how readily H + ions are released HA (aq) + H 2 O (aq) H 3 O + (aq) + A - (aq) K.

SCH 4U.  Ionize only partially in water, exist primarily in molecule form  Dynamic equilibrium established between unreacted molecules and ions formed.

Acid-Base Equilibria Chapter 16. Revision Acids and bases change the colours of certain indicators. Acids and bases neutralize each other. Acids and bases.

Acids and Bases  Arrhenius ◦ Acid:Substance that, when dissolved in water, increases the concentration of hydrogen ions. ◦ Base:Substance that, when dissolved.

Chapter 16 Acid–Base Equilibria

14.1 Intro to Acids and Bases 14.2 Acid Strength 14.3 pH Scale

PART 3: Weak Acids & Bases Unit 08 IB Topics 8 & 18 Chapters 14 & 15.

3 Acids, Bases, and Buffers

Weak Acids & Weak Bases. Review Try the next two questions to see what you remember Try the next two questions to see what you remember.

Acid-Base Strength: Ka, Kb, Kw Mrs. Kay Chemistry 12 Chapter 15 Pages: ,

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book 2 1 Chapter 17 Acid-base Equilibrium I : The Basic Concepts 17.1Concept of Acid and Base.

Acid Base Equilibrium CH 16. Some Definitions Arrhenius Acid:Substance that, when dissolved in water, increases the concentration of hydrogen ions. Base:Substance.

Acids and Bases Chapter 16 Acids and Bases. Acids and Bases Some Definitions Arrhenius  ________________:Substance that, when dissolved in water, increases.

Title: Lesson 7: K a /pK a and K b /pK b Learning Objectives: – Understand the concepts of K a and K b – Understand the concepts of pK a and pK b.

Strength of Acids and Bases Do they ionize 100%?.

Acids and Bases Chapter 14. Classifying Acids Organic acids contain a carboxyl group or -COOH -- HC 2 H 3 O 2 & citric acid. Inorganic acids -- HCl, H.

C. Y. Yeung (CHW, 2009) p.01 Acid-Base Eqm (4): Buffer Solutions Q.:What is the new pH after addition of mol HCl at 298K? (assume no volume change)

Strong base neutralizes weak acid Strong acid neutralizes weak base.

Buffers. A buffer is a solution whose pH is resistant to change on the addition of relatively small quantities of an acid or base. Buffers have the ability.

Weak acid and base calculations. What’s so hard? Unlike strong acids and bases, weak examples do not dissociate fully. For example, a 1 molL -1 HCl solution.

8.3 Bases Similar to weak acids, weak bases react with water to a solution of ions at equilibrium. The general equation is: B(aq) + H2O(l)  HB+(aq) +

Makeup midquarter exams Wed., Mar 9 5:30-7:30 pm 131 Hitchcock Hall You MUST Sign up in 100 CE Please do so as soon as possible.

C. Y. Yeung (CHW, 2009) p.01 Acid-Base Eqm (3): Explain the Strength of Organic Acids & Bases Review Questions Q.1:pK b of CH 3 NH 2 (an organic weak base)

Acid-Base Equilibria Chapter 16. Revision Acids and bases change the colours of certain indicators. Acids and bases neutralize each other. Acids and bases.

1 Acids and Bases - the Three Definitions 1. The Arrhenius Definition of an Acid 2. Acid strength and pK a 3. K a, pK a, pK b 4. polyprotic acids, pK a1,

Starter question. Consider propanoic acid (CH 3 CH 2 COOH) reacting with water….. 1. Write a symbol equation for the equilibrium that is established.

Advanced Acid/Base Theory

ACIDS AND BASES Questions may involve any of the following: description of acids and bases in terms of proton transfer calculations involving K w and pH.

15 Acids and Bases Contents 15-1 The Bronsted-Lowry Definitions 15-2 The Ion Product of Water, Kw 15-3 The pH and Other “p” Scales 15-4 Concentrations.

Acid-Base Equilibria. Some Definitions Arrhenius – An acid is a substance that, when dissolved in water, increases the concentration of hydrogen ions.

ACID-BASE EQUILIBRIUM ERT 207 ANALYTICAL CHEMISTRY SEMESTER 1, ACADEMIC SESSION 2015/16.

Updates Midterms marked; solutions are posted Assignment 03 is in the box Assignment 04 is up on ACME and is due Mon., Feb. 26 (in class)

Titration Curves I. Strong Acid + Strong Base 0.1 M HCl 0.1 M NaOH

3.6: ACIDS AND BASES … Equilibrium Constants…K a and K b.

Calculations Involving Acids and Bases Section 18.1.

Weak Acids & Bases Chapter 16. Dissociation Constants Since weak acids do not dissociate completely, [H 3 O + ] ≠ [acid] For a generalized acid dissociation,

Chapter 16 Acids and Bases. Arrhenius Definition Acids produce hydrogen ions in aqueous solution. Bases produce hydroxide ions when dissolved in water.

Acids, Bases, and Acid-Base Equilibria. Acid-Base Theories and Relative Strengths Arrhenius Theory of acids and bases acid – produces H + ions base –

Models of Acids and Bases Arrhenius Concept: Acids produce H + in solution, bases produce OH  ion. Brønsted-Lowry: Acids are H + donors, bases are proton.

Weak Acids and Bases. “WEAK” Acids and bases that ionize less (much less) than 100% The amount of H 3 O + or OH - in solution is MUCH smaller than the.

Chemistry 100 Acids and Bases. The Brønsted Definitions Brønsted Acid  proton donor Brønsted Base  proton acceptor Conjugate acid - base pair  an acid.

BUFFERS Mixture of an acid and its conjugate base. Buffer solution  resists change in pH when acids or bases are added or when dilution occurs. Mix: A.

CHAPTER 16: ACID BASE EQUILIBRIA Wasilla High School

Acid-Base Strength: Ka, Kb, Kw OR any K really…. Relative Strengths Of Binary Acids H –X The greater the tendency for the transfer of a proton from HX.

C. Y. Yeung (CHW, 2009) p.01 Titration Curves Acid-Base Eqm (5): Titration Curves Titration Curves Acid-Base Eqm (6): Titration Curves Plotting the Titration.

Chapter Fifteen Acids and Bases. Chapter Fifteen/ Acids and Bases acids is a substances that ionize in water to produce H + ions HCl (aq) → H + (aq) +

pH calculations strong acids complete dissociation HA  H+ + A-

PART 2: WEAK A & B EQUILIBRIA

BUFFER SOLUTIONS What is a buffer solution? Definition

pH calculations strong acids complete dissociation HA  H+ + A-

Dissociation Constants

Presentation transcript:

C. Y. Yeung (CHW, 2009) p.01 Acid-Base Eqm (2): K a and K b Review Questions Calculate the pH : Q HCl(aq) [100% ionized] Q.20.01M NaOH(aq) [100% ionized] [H 3 O + ] = ( ) M = 1.1  M,  pH = -log(1.1  ) = 6.96 [OH - ] = 0.01M, pOH = -log(0.01) = -2  pH = 14 – 2 = 12

weak acid p.02 Acid Dissociation Constant (K a ) [temperature dependent!!] HA + H 2 O A - + H 3 O + Kc =Kc =Kc =Kc = [H 3 O + (aq)] [A - (aq)] [HA(aq)] [H 2 O(l)] K c [H 2 O(l)] = [H 3 O + (aq)] [A - (aq)] [HA(aq)] Ka =Ka =Ka =Ka = [HA(aq)]

p.03 Ka =Ka =Ka =Ka = [H 3 O + (aq)] [A - (aq)] [HA(aq)] Q:K a of methanoic acid (HCOOH) at 298K is 1.78  mol dm -3. Calculate the pH value of 1.00M HCOOH. HCOOH + H 2 O HCOO - + H 3 O + at start at eqm – x xx Ka =Ka =Ka =Ka = x2x2x2x2 1 – x = 1.78  x 2 = 1.78  (x << 1,  K a is small) x =  pH = -log(0.0133) = 1.88 solved eqn without approximation, x = , pH = 1.88

p.04 Ka =Ka =Ka =Ka = x2x2x2x – x = 1.78  x 2 = 1.78  (x << 1,  K a is small) x = 1.33   pH = -log(1.33  ) = 2.87 Note: Different conc. of HA has different “% of dissociation” For 1.00M HCOOH, % of dissociation = ( /1)  100% = 1.33 % Q:K a of methanoic acid (HCOOH) at 298K is 1.78  mol dm -3. Calculate the pH value of 0.01 M HCOOH. For 0.01M HCOOH, % of dissociation = (1.242  /0.01)  100% = 12.4 % solved eqn without approximation, x =  10 -3, pH = 2.91 *** i.e. [HA] decreases, % of dissociation increases.

p.05 For Polyprotic Acid : K a1, K a2, ….. [Note: K a1 > K a2 > … ]  WHY? Note:It is more difficult to remove a H + from the negatively charged HSO 4 -. H 2 SO 4 + H 2 O HSO H 3 O + HSO H 2 O SO H 3 O + K a1 K a2 H 3 O + is already produced in the first dissociation, it would suppress the formation of H 3 O + from the second dissociation. [COMMON ION EFFECT (p.148)] Overall K a of Polyprotic acid = K a1  K a2  …

p.06 Q:Assuming that the first ionization of H 2 SO 4 is 100%, and the K a2 of sulphuric acid is 0.01M. Find the pH of 0.10M H 2 SO 4. HSO H 2 O SO H 3 O + K a2 = 0.01M at start at eqm – x x 0.1+x K a2 = x(0.1+x) 0.1 – x = 0.01 x = 8.44   pH = -log (  ) = 0.965

p.07 Importance of K a ?? 1.Indicates the strength of acid: (a)larger K a  stronger acid (b)smaller pK a  stronger acid (ref.: p. 141) 2.Indicates the relative stability of conjugate bases: e.g.K a of ethanoic acid = 1.80  mol dm -3, K a of butanoic acid = 1.48  mol dm -3. i.e.CH 3 CH 2 CH 2 COO - is less stable than CH 3 COO -.

p.08 Base Dissociation Constant (K b ) [temperature dependent!!] B + H 2 O HB + + OH - Kb =Kb =Kb =Kb = [HB + (aq)] [OH - (aq)] [B(aq)] Q:K b of NH 3 at 298 K is 1.78  mol dm -3. What is the pH value of 1M NH 3 at 298K? Kb =Kb =Kb =Kb = x2x2x2x2 1 – x = 1.78  x = 4.22   pOH = -log(4.22  ) = 2.37 pH = 14 – pOH = 11.6 pH = 14 – pOH = 11.6

p.09 Q:K b of NH 3 at 298 K is 1.78  mol dm -3. What is the pH value of a solution which is both 1M NH 3 and 1M NH 4 Cl at 298K? NH 3 + H 2 O NH OH - at start at eqm – x 1+x x Kb =Kb =Kb =Kb =x(1+x) = 1.78  x = 1.78   pOH = -log(1.78  ) = 4.75 pH = = 9.25

p.10 Importance of K b ?? 1.Indicates the strength of base: (a)larger K b  stronger base (b)smaller pK b  stronger base (ref.: p. 142) 2.Indicates the relative stability of conjugate acid: e.g.K b of NH 3 = 1.74  mol dm -3, K b of (CH 3 ) 2 NH = 9,55  mol dm -3. i.e.(CH 3 ) 2 NH 2 + is more stable than NH 4 +.

p.11 Relationship between K w, K a and K b ?? HA + H 2 O A - + H 3 O + Ka =Ka =Ka =Ka = [H 3 O + (aq)] [A - (aq)] [HA(aq)] Kb =Kb =Kb =Kb = [HA(l)] [OH - (aq)] [A - (aq)] A - + H 2 O HA + OH - Ka  Kb =Ka  Kb =Ka  Kb =Ka  Kb = [H 3 O + (aq)] [A - (aq)] [HA(aq)]  [HA(l)] [OH - (aq)] [A - (aq)] [H 3 O + (aq)] [A - (aq)] [HA(aq)]  [HA(l)] [OH - (aq)] [A - (aq)] = K w

Assignment Study all examples in p p.152 Q.3 –12 [due date: 26/3(Thur)] p.12 Next …. Explain the Strength of Organic Acids & Bases (Book 3A p. 113 – 133) Pre-Lab: Expt. 12 Determination of K a

p.13 Expt. 12Dissociation Constant of Weak Acids HA + H 2 O A - + H 3 O + Ka =Ka =Ka =Ka = [H 3 O + (aq)] [A - (aq)] [HA(aq)] log K a = [H 3 O + (aq)] [A - (aq)] [HA(aq)] log pK a = [A - (aq)] [HA(aq)] + log log [H 3 O + (aq)] pK a = [A - (aq)] [HA(aq)] + log pH

p.14 HA + H 2 O A - + H 3 O + pK a = [A - (aq)] [HA(aq)] + log pH Step 6 (10cm 3 NaOH added) 1  mol 0 mol Step 5 1  mol 0 mol Step 7 (another 10cm 3 HA added) 1  mol at eqm 1  mol – x 1  mol + x in the same volume, i.e. same conc.! = pH + log (1) = pH measured by pH meter

p.15 Simple explanation on the Relative Acidity of Organic Acids The more stable is the conjugate base, the more acidic is the acid. 1. If the –ve charge of conjugate base is localized, it is more likely to recombine with the H 3 O + to form the acid again.  the acid is less acidic! 2. If the –ve charge of conjugate base is delocalized, it is less likely to recombine with the H 3 O + to form the acid again.  the acid is more acidic!

p.16 Alkyl group (e.g. CH 3 ) is e - releasing, halo group (e.g. Cl) is e - withdrawing. H C H CH 3 C O O -HC H Cl C O O - e- releasing group e- withdrawing group more stable conjugate base,  ClCH 2 COOH is more acidic! (i.e. larger K a, smaller pK a ) *** Longer alkyl group, more e - realeasing. ***More halogen atoms, more e- withdrawing.