2 Some Properties of Acids Produce H+ (as H3O+) ions in water (the hydronium ion is a hydrogen ion attached to a water molecule)Taste sourCorrode metalsElectrolytesReact with bases to form a salt and waterpH is less than 7Turns blue litmus paper to red “Blue to Red A-CID”
3 Some Properties of Bases Produce OH- ions in waterTaste bitter, chalkyAre electrolytesFeel soapy, slipperyReact with acids to form salts and waterpH greater than 7Turns red litmus paper to blue “Basic Blue”
4 Acid Nomenclature Review No Oxygenw/OxygenAn easy way to remember which goes with which…“In the cafeteria, you ATE something ICky”
5 Acid/Base definitions Definition 1: Arrhenius Arrhenius acid is a substance that produces H+ (H3O+) in waterArrhenius base is a substance that produces OH- in water
6 Acid/Base Definitions Definition #2: Brønsted – LowryAcids – proton donorBases – proton acceptorA “proton” is really just a hydrogen atom that has lost it’s electron!
7 A Brønsted-Lowry acid is a proton donor A Brønsted-Lowry base is a proton acceptorconjugate acidconjugate basebaseacid
8 ACID-BASE THEORIESThe Brønsted definition means NH3 is a BASE in water — and water is itself an ACID
14 The pH scale is a way of expressing the strength of acids and bases The pH scale is a way of expressing the strength of acids and bases. Instead of using very small numbers, we just use the NEGATIVE power of 10 on the Molarity of the H+ (or OH-) ion. Under 7 = acid 7 = neutral Over 7 = base
15 (Remember that the [ ] mean Molarity) Calculating the pHpH = - log [H+](Remember that the [ ] mean Molarity)Example: If [H+] = 1 X pH = - log 1 X 10-10pH = - (- 10)pH = 10Example: If [H+] = 1.8 X 10-5 pH = - log 1.8 X 10-5pH = - (- 4.74)pH = 4.74
16 Try These! pH = - log [H+] pH = - log 0.15 pH = - (- 0.82) pH = 0.82 pH = - log 3 X 10-7pH = - (- 6.52)pH = 6.52Find the pH of these:A 0.15 M solution of Hydrochloric acid2) A 3.00 X 10-7 M solution of Nitric acid
17 pH calculations – Solving for H+ If the pH of Coke is 3.12, [H+] = ???Because pH = - log [H+] then- pH = log [H+]Take antilog (10x) of both sides and get10-pH = [H+][H+] = = 7.6 x 10-4 M*** to find antilog on your calculator, look for “Shift” or “2nd function” and then the log button
18 More About Water Equilibrium constant for water = Kw H2O can function as both an ACID and a BASE.In pure water there can be AUTOIONIZATIONEquilibrium constant for water = KwKw = [H3O+] [OH-] = x at 25 oC
19 More About Water and so [H3O+] = [OH-] = 1.00 x 10-7 M Autoionization Kw = [H3O+] [OH-] = x at 25 oCIn a neutral solution [H3O+] = [OH-]and so [H3O+] = [OH-] = 1.00 x 10-7 M
20 pOH Since acids and bases are opposites, pH and pOH are opposites! pOH does not really exist, but it is useful for changing bases to pH.pOH looks at the perspective of a basepOH = - log [OH-]Since pH and pOH are on opposite ends,pH + pOH = 14
22 [H3O+], [OH-] and pH What is the pH of the 0.0010 M NaOH solution? [OH-] = (or 1.0 X 10-3 M)pOH = - logpOH = 3pH = 14 – 3 = 11OR Kw = [H3O+] [OH-][H3O+] = 1.0 x MpH = - log (1.0 x 10-11) = 11.00
23 What is the pH of a 2 x 10-3 M HNO3 solution? HNO3 is a strong acid – 100% dissociation.Start0.002 M0.0 M0.0 MHNO3 (aq) + H2O (l) H3O+ (aq) + NO3- (aq)End0.0 M0.002 M0.002 MpH = -log [H+] = -log [H3O+] = -log(0.002) = 2.7What is the pH of a 1.8 x 10-2 M Ba(OH)2 solution?Ba(OH)2 is a strong base – 100% dissociation.Start0.018 M0.0 M0.0 MBa(OH)2 (s) Ba2+ (aq) + 2OH- (aq)End0.0 M0.018 M0.036 MpH = – pOH = log(0.036) = 12.56
24 Strong and Weak Acids/Bases The strength of an acid (or base) is determined by the amount of IONIZATION.HNO3, HCl, HBr, HI, H2SO4 and HClO4 are the strong acids.
25 Strong and Weak Acids/Bases Generally divide acids and bases into STRONG or WEAK ones.STRONG ACID: HNO3 (aq) + H2O (l) H3O+ (aq) NO3- (aq)HNO3 is about 100% dissociated in water.
26 Strong and Weak Acids/Bases Weak acids are much less than 100% ionized in water.*One of the best known is acetic acid = CH3CO2H
27 Strong and Weak Acids/Bases Strong Base: 100% dissociated in water.NaOH (aq) Na+ (aq) + OH- (aq)Other common strong bases include KOH and Ca(OH)2.CaO (lime) + H2O -->Ca(OH)2 (slaked lime)CaOStrong bases are the group I hydroxidesCalcium, strontium, and barium hydroxides are strong, but only soluble in water to 0.01 M
28 Strong and Weak Acids/Bases Weak base: less than 100% ionized in waterOne of the best known weak bases is ammoniaNH3 (aq) + H2O (l) ↔ NH4+ (aq) + OH- (aq)
30 Equilibria Involving Weak Acids and Bases Consider acetic acid, HC2H3O2 (HOAc)HC2H3O2 + H2O ↔ H3O C2H3O2 -Acid Conj. base(K is designated Ka for ACID)K gives the ratio of ions (split up) to molecules (don’t split up)
31 Ionization Constants for Acids/Bases ConjugateBasesIncrease strengthIncrease strength
32 Equilibrium Constants for Weak Acids Weak acid has Ka < 1Leads to small [H3O+] and a pH of 2 - 7
33 Equilibria Involving A Weak Acid You have 1.00 M HOAc. Calc. the equilibrium concs. of HOAc, H3O+, OAc-, and the pH.Step 1. Define equilibrium concs. in ICE table.[HOAc] [H3O+] [OAc-]initialchangeequilib-x +x +x1.00-x x x
34 Equilibria Involving A Weak Acid You have 1.00 M HOAc. Calc. the equilibrium concs. of HOAc, H3O+, OAc-, and the pH.Step 2. Write Ka expressionThis is a quadratic. Solve using quadratic formula.or you can make an approximation if x is very small! (Rule of thumb: 10-5 or smaller is ok)
35 Equilibria Involving A Weak Acid You have 1.00 M HOAc. Calc. the equilibrium concs. of HOAc, H3O+, OAc-, and the pH.Step 3. Solve Ka expressionFirst assume x is very small because Ka is so small.Now we can more easily solve this approximate expression.
36 Equilibria Involving A Weak Acid You have 1.00 M HOAc. Calc. the equilibrium concs. of HOAc, H3O+, OAc-, and the pH.Step 3. Solve Ka approximate expressionx = [H3O+] = [OAc-] = 4.2 x 10-3 MpH = - log [H3O+] = -log (4.2 x 10-3) = 2.37
37 Equilibria Involving A Weak Acid Calculate the pH of a M solution of formic acid, HCO2H.HCO2H H2O ↔ HCO H3O+Ka = 1.8 x 10-4Approximate solution[H3O+] = 4.2 x 10-4 M, pH = 3.37Exact Solution[H3O+] = [HCO2-] = 3.4 x 10-4 M[HCO2H] = x 10-4 = MpH = 3.47
38 Equilibrium Constants for Weak Bases Weak base has Kb < 1Leads to small [OH-] and a pH of
40 Equilibria Involving A Weak Base You have M NH3. Calc. the pH.NH3 + H2O ↔ NH OH-Kb = 1.8 x 10-5Step 1. Define equilibrium concs. in ICE table[NH3] [NH4+] [OH-]initialchangeequilib-x +x +xx x x
41 Equilibria Involving A Weak Base You have M NH3. Calc. the pH.NH3 + H2O NH OH-Kb = 1.8 x 10-5Step 2. Solve the equilibrium expressionAssume x is small, sox = [OH-] = [NH4+] = 4.2 x 10-4 Mand [NH3] = x 10-4 ≈ MThe approximation is valid !
42 Equilibria Involving A Weak Base You have M NH3. Calc. the pH.NH3 + H2O NH OH-Kb = 1.8 x 10-5Step 3. Calculate pH[OH-] = 4.2 x 10-4 Mso pOH = - log [OH-] = 3.37Because pH + pOH = 14,pH = 10.63
44 Weak Bases are weak electrolytes F- (aq) + H2O (l) OH- (aq) + HF (aq)NO2- (aq) + H2O (l) OH- (aq) + HNO2 (aq)Conjugate acid-base pairs:The conjugate base of a strong acid has no measurable strength.H3O+ is the strongest acid that can exist in aqueous solution.The OH- ion is the strongest base that can exist in aqueous solution.
47 For a monoprotic acid HA Ionized acid concentration at equilibriumInitial concentration of acidx 100%percent ionization =For a monoprotic acid HAPercent ionization =[H+][HA]0x 100%[HA]0 = initial concentration
48 Ionization Constants of Conjugate Acid-Base Pairs HA (aq) H+ (aq) + A- (aq)KaA- (aq) + H2O (l) OH- (aq) + HA (aq)KbH2O (l) H+ (aq) + OH- (aq)KwKaKb = KwWeak Acid and Its Conjugate BaseKa =KwKbKb =KwKa
49 Molecular Structure and Acid Strength H XH+ + X-Bond strengthPolarityThe stronger the bondThe weaker the acidHF << HCl < HBr < HI
50 Molecular Structure and Acid Strength ZOHO-+ H+d-d+The O-H bond will be more polar and easier to break if:Z is very electronegative orZ is in a high oxidation state
51 Molecular Structure and Acid Strength 1. Oxoacids having different central atoms (Z) that are from the same group and that have the same oxidation number.Acid strength increases with increasing electronegativity of ZH O Cl OO•H O Br OO•Cl is more electronegative than BrHClO3 > HBrO315.9
52 Molecular Structure and Acid Strength 2. Oxoacids having the same central atom (Z) but different numbers of attached groups.Acid strength increases as the oxidation number of Z increases.HClO4 > HClO3 > HClO2 > HClO
53 Acid-Base Properties of Salts Neutral Solutions:Salts containing an alkali metal or alkaline earth metal ion (except Be2+) and the conjugate base of a strong acid (e.g. Cl-, Br-, and NO3-).NaCl (s) Na+ (aq) + Cl- (aq)H2OBasic Solutions:Salts derived from a strong base and a weak acid.NaCH3COO (s) Na+ (aq) + CH3COO- (aq)H2OCH3COO- (aq) + H2O (l) CH3COOH (aq) + OH- (aq)
54 Acid-Base Properties of Salts Acid Solutions:Salts derived from a strong acid and a weak base.NH4Cl (s) NH4+ (aq) + Cl- (aq)H2ONH4+ (aq) NH3 (aq) + H+ (aq)Salts with small, highly charged metal cations (e.g. Al3+, Cr3+, and Be2+) and the conjugate base of a strong acid.Al(H2O)6 (aq) Al(OH)(H2O)5 (aq) + H+ (aq)3+2+
55 Acid-Base Properties of Salts Solutions in which both the cation and the anion hydrolyze:Kb for the anion > Ka for the cation, solution will be basicKb for the anion < Ka for the cation, solution will be acidicKb for the anion Ka for the cation, solution will be neutral