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ACID BASE CHEMISTRY

ACID BASE CHEMISTRY. TERMS, ETC. AMPHOTERIC:. Subst. acts as either an acid or a base. H + ion; the acidic hydrogen(s) present in an acid. Proton (Acidic p + ):. H 2 SO 4 : two H +. HNO 3 : one H +. H 3 PO 4 : three H +. MONOPROTIC ACID:. An acid w/ one H +. DIPROTIC ACID:.

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ACID BASE CHEMISTRY

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  1. ACID BASE CHEMISTRY TERMS, ETC. AMPHOTERIC: Subst. acts as either an acid or a base H+ ion; the acidic hydrogen(s) present in an acid Proton (Acidic p+): H2SO4: two H+ HNO3: one H+ H3PO4: three H+ MONOPROTIC ACID: An acid w/ one H+ DIPROTIC ACID: An acid w/ two H+ POLYPROTIC ACID: An acid w/ 3 or more H+ HYDRONIUM ION: H2O (l) + H+1 (aq) ---------> H3O+1(aq) H+; a hydrogen w/ characteristics like a proton itself -----1 p+, 0 n0, 0 e- Proton:

  2. Acid BASE All acids contain H+; when in water give solution higher [H+] All bases contain OH-; when in water give solution higher [OH-] Arrhenius

  3. Acid BASE Any subst. that accepts a proton; H+ BRONSTAD – LOWRY Any subst. that donates a proton; H+ LEWIS Any subst. that donates an e- pair Any subst. that accepts an e- pair

  4. BASES ACIDS • Taste sour • Turns litmus blue -- red • Lowers pH • Feels slippery • Turns litmus red -- blue • Increases pH The stronger the acid the better it is at donating H+ STRONG ACIDS HCl ; HBr ; HI ; HNO3 ; H2SO4 ; HClO4 2H++SO4-2 H++I- H++Cl-

  5. pH SCALE 0 7 14 NEUTRAL ( ) MILD ACIDIC MILD BASIC WEAK ACIDIC WEAK BASIC STRONG ACIDIC STRONG BASIC Kw: constant for water, 1*10-14 ACID-BASE REACTIONS HCl (aq) + KOH (aq) ---> KCl (aq) + HOH (l) acid base salt water

  6. Formulas to Use Constants pH -- pOH -- [H+] -- [OH-] CALCULATIONS Kw = 1 *10 –14 pKw = 14 pH = -log [H+] pOH = -log [OH-] Rules for LOGS [H+] = 1*10-pH Log 1 = 0 [OH-] = 1*10-pOH Log 10exp = exponent

  7. Rules for LOGS

  8. Calculate pH for the following solutions 1) [H+] = 1 * 10-9 pH = -log (1*10-9) = -(-9) = 9 2) [H+] = 0.001 0.001 = 1*10-3 pH = -log (1*10-3) = -(-3) = 3

  9. Find pH & pOH 3) [H+] = 3.6 * 10-2 pH = -log(3.6*10-2) = 1.44 pH = 2 – log (3.6) = 2 – 0.56 = 1.44 -log 10-2 = 2 OR pKw = pH + pOH 14 = 1.44 + pOH pOH = 14 – 1.44 = 12.56 pOH OR = 2.78*10-13 pOH = 13 – log 2.78 = 13 – 0.44 =

  10. 1*10-14 [OH-] = 6.7*10-9 If [H+] is 6.7*10-9 mol/L, what is the pH? ACIDIC, BASIC, NEUTRAL What is the [OH-]? What is the pOH? Find pH Find pOH pH = -log(6.7*10-9) = 9 – log 6.7 = 9 – 0.83 = 8.17 pOH = 14 – 8.17 = 5.83 Find [OH-] BASIC [OH-] = 1*10-5.83 OR = 1.49*10-6

  11. CONJUGATE ACID-BASE PAIRS Acid, loses H+, form conjugate base Base, gains H+, forms conjugate acid base2 base1 acid1 acid2 CONJUGATE ACID-BASE PAIRS

  12. TITRATIONS Strong Acid + Strong Base ------ Neutral +/- ions of acid not react w/ H2O Strong Acid + Weak Base --- Acidic “+” ion of strong acid reacts w/ H2O, produces H3O+ Weak Acid + Strong Base --- Basic “-” ion of strong base reacts to produce OH- ions Weak Acid + Weak Base ---- ??????? Both +/- ions react w/ H2O

  13. IONIZATION CONSTANTS STRENGTH Strong Acid/Base ionize completely equilibrium lies far to the right HCl ------> H+ + Cl- NaOH -----> Na+ + OH- Weak Acid slightly ionize equilibrium lies far to the left HC2H3O2 + H2O <-----> H+ + C2H3O2- Ka: acid dissociation constant Kb: base dissociation constant

  14. Ka acetic acid = 1.8*10-5 Ka nitrous acid = 4.4*10-4 nitrous acid more ionized in soln BASE NH3 + H2O <---> NH4+ +OH- Kb ammonia = 1.8*10-5

  15. ACID BASE HCN _________ _______ OH-1 HSO4-1 ________ _______ C2H3O2-1 _______ C2O4-2 ______ NH3 Find the Missing Part ??? CN-1 H2O SO4-2 HC2H3O2 HC2O4-1 NH4+1

  16. Increasing base strength Increasing acid strength S.A. yields weak conjugate base W.A. yields strong conj. base MONOPROTIC ACIDS pg. 300 Ka Acid Kb Conj. Base 8.3*10-13 SO4-2 8.3*10-13 ClO2- 1.4*10-11 F- 5.56*10-10 C2H3O2- 2.9*10-7 OCl- 1.8*10-5 NH3 1.2*10-2 HSO4- 1.2*10-2 HClO2 7.2*10-4 HF 1.8*10-5 HC2H3O2 3.5*10-8 HOCl 5.6*10-10 NH4+

  17. conj. base strength acid strength Very Strong Very Weak Strong Weak Weak Strong Very Weak Very Strong

  18. Diprotic & Triprotic Acids H2CO3: 2 acidic protons Ka values for each H+ Ka1 = 4.3*10-7 Ka2 = 5.6*10-11 typically weak polyprotic acid Ka1 > Ka2 > Ka3 means???? -each step of dissociation is successively weaker -loss of 2nd & 3rd proton occurs less readily Why???? should not be surprising think in terms of charges, +/- being attracted

  19. S.A. : Ka 10-1 --- 10-3 W.A.: Ka 10-4 & smaller S.B.: Kb???? Polyprotic acid: Ka value lowers w/ each H+ lost Loss of each additional H+ more difficult H3PO4 + H2O <-----> H3O+ + H2PO4- Ka1 H2PO4- + H2O <-----> H3O+ + HPO4-2 Ka2 HPO4-2 + H2O <-----> H3O+ + PO4-3 Ka3 Ka1 >Ka2 > Ka3 10-3 10-8 10-13

  20. Ka: acid dissociation constant HA + H2O <-----> H3O+ + A- HNO3 + H2O <-----> H3O+ + NO3-

  21. BUFFER -used to control pH level of a soln. -either remove H+ or add OH- ions -usually W.A. & conj. Base TITRATION S.A. + W.B. -------> Acidic W.A. + S.B. -------> Basic S.A. + S.B. -------> Neutral W.A. + W.B. -----> ?? more info. S.A. ------> weak conjugate Base W.A. -----> strong conj. Base

  22. Property S.A. W.A. [H+] [HA]o Various Ways to Describe Acid Strength Ka value Ka is large Ka is small Position of dissociation equilibrium Far to left Far to right Equilibrium [H+] compared to [HA]o [H+]<<[HA]o A- much weaker acid than H2O Strength of conj.base compared to H2O A- much stronger base than H2O

  23. INTERMOLECULAR FORCES Forces that act between diff. molecules Gases: <<< forces, act independently of each other Liquids/Solids: >>>> Forces KEY PTS. Stronger the Force -------- more difficult to separate atoms/molecules ---- higher melting/boiling pts of subst.

  24. Weak Force; as mole.wt. 3 MAJOR FORCES Dipole-Dipole London Dispersion Hydrogen Bonding London Dispersion Dipole-Dipole Polar Cov. Bonds “net polarity” All molecules; behavior due to e- movement w/i subst. Nonpolar molecules form temporary Polarity Weak Force +/- ends of molecules align together Surface Area: > S.A. ---- > Force stronger the molecule held together

  25. .. .. .. .. .. .. N O O .. F .. H .. .. .. Cl H H H H .. .. H F .. Hydrogen Bonding Strong bond Force H bonded to an O, N, or F of one molecule; that H will be attracted to unshared e- pair of O, N, or F of another molecule

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