Ch 15: Slides (Acids and Bases)

Ch 15: Slides (Acids and Bases)

Acid/Base Definitions
Chapter 15: Acids and Bases General Chem (Dunn) 9/11/2018 Acid/Base Definitions Lewis Bronsted-Lowry Arrhenius Arrhenius Acids and Bases Acid: Released H+ in water (H3O+) Base: Releases OH- in water Bronsted-Lowry Acid: Proton (H+) Donor Base: Proton (H+) Acceptor Lewis Acid: Electron pair Acceptor Base: Electron pair Acceptor Which definition is the most narrow? Which is the most broad? Come back to this question after slide 10 Ch 15: Slides (Acids and Bases)

Chapter 15: Acids and Bases General Chem (Dunn)
Lewis Bronsted-Lowry Arrhenius HNO3 (aq) H+ + NO3- 9/11/2018 3. Write a reaction for HNO3(aq) showing that it is an Arrhenius acid: What is the relationship between H+(aq) and H3O+(aq) ? Why is H+ often referred to as a proton? HNO3 + H2O  H3O+ + NO3- Ch 15: Slides (Acids and Bases)

Rank the following solutions from most acidic to most basic (water molecules have been omitted for clarity). Ch 15: Slides (Acids and Bases)

9/11/2018 Lewis Bronsted-Lowry Arrhenius H+ Show the proton (H+) transfer in this Bronsted-Lowry Acid/Base reaction H3O NH3 ⇌ H2O + NH4+ Which compound is the acid? Why? Which compound is the base? Why? Could this example be used for an Arrhenius acid/base? Conjugate Acid/Base Pairs: Consider the backwards reaction Which compound is the base? Why? Ch 15: Slides (Acids and Bases)

9/11/2018 Lewis Bronsted-Lowry Arrhenius HNO H2O  H3O NO3- Show the proton (H+) transfer in this Bronsted-Lowry Acid/Base reaction HNO H2O  H3O NO3- Which compound is the acid? Why? Which compound is the base? Why? Label the CONJUGATE Acid and CONJUGATE Base How did you figure out the conjugates? Could this example be used to illustrate an Arrhenius acid/base reaction? Explain Ch 15: Slides (Acids and Bases)

Codeine, C18H21O3N is a BL base…
Chapter 15: Acids and Bases General Chem (Dunn) 9/11/2018 Codeine, C18H21O3N is a BL base… What is the conjugate acid of codeine? Write a net ionic equation to show codeine behaving as a BL base in water. Identify the acid/base pairs 7. Codeine, C18H21O3N is a Bronsted-Lowry (BL) base… What is the conjugate acid of codeine? Write a net ionic equation to show codeine behaving as a BL base in water. Label the acid/base pairs Note Nitrogen containing compounds (neutral charge) often behave a BL bases. Ch 15: Slides (Acids and Bases)

Water is amphoteric Give an example of water acting as an ACID (BL) Give an example of water acting as a BASE (BL) Ch 15: Slides (Acids and Bases)

Lewis Bronsted-Lowry Arrhenius - 9/11/2018 Ch 15: Slides (Acids and Bases)

Ammonia is A Base? By All three definitions
Write an example showing each definition: Ch 15: Slides (Acids and Bases)

What does it mean for an acid to be “strong”?
Chapter 15: Acids and Bases General Chem (Dunn) 9/11/2018 What does it mean for an acid to be “strong”? What do the symbols mean? What are the differences between a strong acid and weak acid: Degree of ionization Composition of aqueous solution Conductor of electricity Anything else? See phet on acids and bases Ch 15: Slides (Acids and Bases)

What does it mean for an acid to be “strong”?
HCl is a ________________ ______________ because: Write the reaction (BL) Ch 15: Slides (Acids and Bases)

What does it mean for an acid to be “weak”?
HF is a ________________ ______________ because: Write the reaction (BL) Ch 15: Slides (Acids and Bases)

9/11/2018 Strength of Bases Strong Base – Ionizes completely in aqueous solution Weak Base NH3 + H2O ⇌ NH4+ + H3O+ What is the solution composition of each? Ch 15: Slides (Acids and Bases)

The Strong Acids/Bases
These should be Memorized! Strong acids HClO4 H2SO4 HNO3 HCl HBr HI Strong bases LiOH NaOH KOH Ca(OH)2 Sr(OH)2 Ba(OH)2 If it does not appear on this list it is WEAK! Ch 15: Slides (Acids and Bases)

9/11/2018 Relative Strengths of Acids and Bases The stronger an acid, the weaker its conjugate base. The weaker an acid, the stronger its conjugate base. Ch 15: Slides (Acids and Bases)

9/11/2018 Ch 15: Slides (Acids and Bases)

Write the BL reaction equation for: Generic weak acid in water. Generic anion (base) in water. BL reaction of formic acid with water. BL reaction of Acetic acid in water. BL reaction equation of formate ion in water. Write the reaction of acetate ion in water. 9/11/2018 Formic acid, HCHO2, is a stronger acid than acetic acid, HC2H3O2. Which is the stronger base: formate ion, CHO2−, or acetate ion, C2H3O2−? Formic acid, HCHO2, is a stronger acid than acetic acid, HC2H3O2. Which is the stronger base: formate ion, CHO2−, or acetate ion, C2H3O2−? Write the BL reaction of formic acid with water. Write the BL reaction of Acetic acid in water. Write the BL reaction equation of formate ion in water. Write the reaction of acetate ion in water. The acetate ion is a stronger base than the formate ion. Ch 15: Slides (Acids and Bases)

Structure and Acid Strength : The issue
HOW EASILY IS THE PROTON REMOVED Easily removed = ______________ Tightly held = __________________ Ch 15: Slides (Acids and Bases)

#1 Strength of bond depends on size of atom How does bond strength correspond to acid strength? H-X; large X = strong acid Within a column (group), size is the main issue Compare acid strength HF, HCl, HBr, HI Ch 15: Slides (Acids and Bases)

#2 The first one is easy…… (polyprotic acids)
H2SO4 vs HSO4- H3PO4 vs H2PO4 vs HPO42- Ch 15: Slides (Acids and Bases)

#3 Structure and Acid Strength : The more polarized the bond, the greater the acid strength Polarized bond Electron with drawing groups weaken the bond to H Think electronegativity Across a row (period), this is the most important factor Ch 15: Slides (Acids and Bases)

#3 Structure and Acid Strength : The more polarized the bond, the greater the acid strength Electron with drawing groups weaken the bond to H COMPARE: H3N, H2O, HF Ch 15: Slides (Acids and Bases)

#3 Structure and Acid Strength : The more polarized the bond, the greater the acid strength Electron with drawing groups weaken the bond to H Look down chain: Ch 15: Slides (Acids and Bases)

Not all H’s are equally acidic
Ch 15: Slides (Acids and Bases)

The ISSUES SUMMARIZED In a column/group SIZE matters (as X gets bigger, acid gets stronger) In a row/period ELECTRON withdrawing matters (more electronegativity = stronger acid) Don’t forget to look down chain In a polyprotic acid, the first one is easy (more H’s= stronger acid) Ch 15: Slides (Acids and Bases)

STRUCTURE/STRENGTH OF ACID Concept check
Which is the stronger acid? KEY ISSUE CONCLUSION JUSTIFICATION NH3 or PH3 HI or H2Te H2SO3 or HSO3- H3AsO4 or H3PO4 HSO4- or HSeO4- Ch 15: Slides (Acids and Bases)

9/11/2018 IF the conjugate base is resonance stabilized THEN the acid is strong(er).. Info: Resonance structures that increase stability are those that delocalize electrons over the molecule and place negative charge on electronegative atoms. For example, HNO3 is a strong acid and HNO2 is a weak acid because HNO3 has more resonance structures that place the negative charge on difference oxygen atoms. Questions: Draw the Lewis resonance structures of NO3- and NO2- and use them to explain why nitric acid is a strong acid and nitrous acid is a weak acid. Ch 15: Slides (Acids and Bases)

Application questions
Explain why ethanol ( ) is considerably more acidic than ethane (CH3CH3). Give one reason why acetic acid ( ) is a stronger acid than ethanol? . , is the most acidic. Explain your reasoning Predict which hydrogen in aspartic acid, Ch 15: Slides (Acids and Bases)

Determining the position of Equilibrium: The crabapple analogy
Chapter 15: Acids and Bases General Chem (Dunn) 9/11/2018 Determining the position of Equilibrium: The crabapple analogy Think of the “crab apple” as the proton Strength of acid refers to how quickly or aggressively those crab apples are thrown. This is a “WAR” of the acids The crabapple analogy Think of the “crab apple” as the proton Strength of acid refers to how quickly or aggressively those crab apples are thrown. This is a “WAR” of the acids Ch 15: Slides (Acids and Bases)

Chapter 8: Acids and Bases

Boy Throws apples across the fence.
Chapter 8: Acids and Bases

Old man is a slow runner, but his apples are close at hand.
Old Man Fights Back. Boy is faster, but he has to run around gathering apples. Old man is a slow runner, but his apples are close at hand. Chapter 8: Acids and Bases

Acid-Base Equilibrium
Chapter 15: Acids and Bases General Chem (Dunn) 9/11/2018 How do we determine equilibrium position? Identify the acids (one on each side) Which acid is stronger: (See table) Identify the stronger base (the stronger acid gives the weaker conjugate base) Strongest acid and base react to give weaker acid and base Example: CH3COOH NH ⇌ CH3COO- + NH4+ Strength of acids

Table 9.2For the following reaction, equilibrium lies to the ________ because ________ is the stronger acid. {image} Chapter 15: Acids and Bases General Chem (Dunn) For the following reaction, equilibrium lies to the _____ because _____ is the stronger acid. C6H5OH + H2PO ? H3PO4 + C6H5O- 9/11/2018 left; C6H5OH right; C6H5OH left; H3PO4 right; H3PO4 Left; C6H5OH Right; C6H5OH Left; H3PO4 Right; H3PO4

Acidic and Basic Properties of Pure Water
Acids make H3O+ and bases produce OH- ions What goes on in pure water with no acid or base? Small amounts of ions are present! Ch 15: Slides (Acids and Bases)

Auto-ionization of water
Amphoteric Water H2O(l) + H2O(l)  H3O+(aq) + OH-(aq) Auto-ionization of water Soooo... K = [H3O+] [OH-] Kw = [H3O+] [OH-] [H2O][H2O] Kw, the ion product of water Ch 15: Slides (Acids and Bases)

Meaning of “p” in pH and pOH
Ch 15: Slides (Acids and Bases)

SIG FIG RULE of Logs: # of digits in the mantissa = # of sig figs in the original number log(3.000x104) =4.4771 log(3x104) = 4.5 antilog(0.301) = 2.00 antilog(0.30) = 2.0 Ch 15: Slides (Acids and Bases)

Prove the relationships and/or practice (pH/pOH worksheet)
Chapter 15: Acids and Bases General Chem (Dunn) 9/11/2018 Prove the relationships and/or practice (pH/pOH worksheet) Ch 15: Slides (Acids and Bases)

pH Scale Acidic/basic pH pOH Example solution [H+] (M) [ OH-] (M) 1 M HCl 1 Gastric juices pH= 2 Lemon Juice 3 Vinegar/Diet Coke 4 Tomato Juice 5 Coffee 6 Unpolluted rain 7 Pure water 8 Pancreatic fluid 9 Soap 10 Milk of Magnesia 11 12 Household Ammonia 13 14 Lye (1.0 M NaOH) Ch 15: Slides (Acids and Bases)

[OH-] pH pOH Acid/Base/or Neutral 1.0E-6 M 1.0E-8 M 9.00 7.00 2.5E-9M 3.3E-5 M 3.25 9.6 Ch 15: Slides (Acids and Bases)

[OH-] pH pOH Acid/Base/or Neutral 3.8E-6 M 9.4E-8 M 9.55 6.53 6.8E-9M 1.6E-5 M 2.25 6.75 Ch 15: Slides (Acids and Bases)

pH strategy problems 9/11/2018 You want to make up 3.00 L of aqueous hydrochloric acid, HCl(aq), that has a pH of How many grams of concentrated hydrochloric acid will you need? Concentrated hydrochloric acid contains 37.2 % HCl (wt/wt). This problem is an application of the following concepts: pH scale Degree of ionization of a strong acid Concentration terms, definitions and conversion between different terms (strict unit analysis). Dilution 1. Find [H3O+] pH = 2.00, [H3O+] =0.0100M Ch 15: Slides (Acids and Bases)

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Ch 15: Slides (Acids and Bases)

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