2 Students will learn… 3 definitions of Acids and Bases Acid Strength – pH scaleWater as acid and baseCalculating pH of strong acids and basesBuffered solutions*Review naming acids, Pg 132 & 133
3 Three Definitions of Acids-Bases ArrheniusBrØnsted-LowryLewis
4 3 Definitions of Acids and Bases ArrheniusProduce H+ ion* (= proton)Produce OH– ionBrØnsted-LowryDonate H+ ionsAccept H+ ionsLewisAccept an electron-pairDonate an electron-pair*H+ ion always combines with water molecule, forming hydronium ion, H3O+
5 Arrhenius Acids: HCl, HC2H3O2, HCN Arrhenius Bases: NaOH, Ca(OH)2 BrØnsted-Lowry Acids and Bases: can only be determined from chemical equationsH2O + HCl → H3O+ + Cl-base acid conjugate conjugateacid baseconjugate pairconjugate pair
6 Conjugate Acid-Base Pair An acid and a base that only differ by one H+ ionAlways made of one reactant and one productOften in reversable reactions(Ex) HSO4- + H2O ↔ SO42- + H3O+acid base base acidHSO4- + H2O ↔ H2SO4 + OH-base acid acid base
7 Examples1. Which of the following represent conjugate acid–base pairs? a) HCl, HNO3 b) H3O+, OH– c) H2SO4, SO42– d) HCN, CN–
8 2. Write the conjugate base for each of the following. HClO4H3PO4CH3NH3+
9 Strong vs. Weak Strong: 100% dissociation of H+ or OH– Strong electrolytes (conduct electricity very well)Weak: Less than 100% dissociation of H+ or OH–Weak electrolytes (conduct electricity somewhat)
10 Common Strong and Weak Acids/Bases Strong acids: H+7A, H2SO4, HClO4, HNO3Weak acids: HCN, HC2H3O2Strong bases: 1A+OH, Sr(OH)2, Ba(OH)2Weak bases: NH3 (ammonia) in water = NH4OH (ammonium hydroxide)
12 ExampleAcetic acid (HC2H3O2) and HCN are both weak acids. Acetic acid is a stronger acid than HCN. Arrange these bases from weakest to strongest : Cl– CN– C2H3O2–
13 Terms related AcidsAmphoteric: Ions or molecules that can become an acid and a base(Ex) HSO4- + H2O → SO42- + H3O+acid baseHSO4- + H2O → H2SO4 + OH-base acid(Ex) H2O + H2O → H3O+ + OH-Oxyacids: acids containing oxygen(Ex) HNO3, H2SO4, HClO
14 Monoprotic Acids Diprotic Acids Triprotic Acids Have one proton (H+) to donate(Ex) HCl, HNO3, HI, HClO3Diprotic AcidsHave more than two protons to donate(Ex) H2SO4Triprotic AcidsHave three protons to donate(Ex) H3PO4
15 Self-ionization of Water In neutral water,H2O + H2O ↔ H3O+ + OH–[H3O+] = [OH–] = 1×10-7 mol/L[H3O+] · [OH–] = (1×10-7)·(1×10-7)=1× @ 25 °= KwKw = ion-product constant for water*The constant changes to the temperature
17 Common Misunderstanding An acidic solution has only H+ ionsA basic solution has only OH‒ ions
18 Example(1) In an acidic aqueous solution, which statement below is correct?a) [H+] < 1.0 × 10–7 Mb) [H+] > 1.0 × 10–7 Mc) [OH–] > 1.0 × 10–7 Md) [H+] < [OH–]
19 (2) In an aqueous solution in which [OH–] = 2 (2) In an aqueous solution in which [OH–] = 2.0 x 10–10 M, the [H+] = ________ M, and the solution is ________.a) 2.0 × 10–10 M ; basicb) 1.0 × 10–14 M ; acidicc) 5.0 × 10–5 M ; acidic5.0 × 10–5 M ; basic
20 pH and pOH Scale pH = –log[H+] [H+] = 10-pH pOH = ‒log [OH‒] A compact way to represent solution aciditypH decreases as [H+] increases[H+] = 10-pHpOH = ‒log [OH‒]pOH decreases as [OH‒] increases[OH‒] = 10-pOHpH + pOH = 14
21 pH = 7; neutralpH > 7; basicHigher the pH, more basic.pH < 7; acidicLower the pH, more acidic.
22 Acidity and pH Scalehigh pH = weak acidhigh pOH = weak base
23 Examples (1) Calculate the pH for each of the following solutions. 1.0 × 10–4 M H+b) M OH–
24 (2) The pH of a solution is 5.85. What is the [H+] for this solution?
25 (3) Consider an aqueous solution of 2. 0 × 10–3 M HCl. What is the pH (3) Consider an aqueous solution of 2.0 × 10–3 M HCl. What is the pH? *If the solution was 2.0 × 10–3 M HNO2, a weak acid, you can’t take the same approach. Why?
26 Buffered Solutionsresists a change in its pH when either an acid or a base has been added.Presence of a weak acid and its conjugate base buffers the solution.
27 Characteristics of Buffered Solutions The solution contains a weak acid HA and its conjugate base A–.The buffer resists changes in pH by reacting with any added H+ or OH– so that these ions do not accumulate.Any added H+ reacts with the base A–.H+(aq) + A–(aq) → HA(aq)4. Any added OH– reacts with the weak acid HA.OH–(aq) + HA(aq) → H2O(l) + A–(aq)
28 ExampleIf a solution is buffered with NH3 to which has been added NH4Cl, what reaction will occur if a strong base such as NaOH is added?a) NaOH + NH3 → NaNH4Ob) NaOH + NH4+ → Na+ + NH3 + H2Oc) NaOH + Cl– → NaCl + OH–d) NaOH + H2O → NaH3O2