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ACIDS AND BASES

ACIDS AND BASES. Dissociation Constants. weaker the acid, the stronger its conjugate base. stronger the acid, the weaker its conjugate base. weaker the base, the stronger its conjugate acid. stronger the base, the weaker its conjugate acid. Write equilibrium expression for an acid or base

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ACIDS AND BASES

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  1. ACIDS AND BASES Dissociation Constants

  2. weaker the acid, the stronger its conjugate base stronger the acid, the weaker its conjugate base

  3. weaker the base, the stronger its conjugate acid stronger the base, the weaker its conjugate acid

  4. Write equilibrium expression for an acid or base • Calculate the acid/base dissociation constant • Calculate the percent dissociation

  5. HA(aq) H+(aq) + A-(aq) HA(aq) + H2O(l) H3O+(aq) + A-(aq) Strong Acid Weak Acid Ka - acid dissociation constant Larger Ka : strong acid: more product : more H+.

  6. BOH(aq) B+(aq) + OH-(aq) B(aq) + H2O(l) BH+(aq) + OH-(aq) Strong Base Weak Base Kb - base dissociation constant Larger Kb : strong base : more product : more OH-.

  7. CH3COOH(aq) + H2O(l) H3O+(aq) + C2H3O2¯(aq) Initially a 0.10 M solution of acetic acid, it reached equilibrium with a [H3O+] = 1.3 x 10-3 M. What is the acid dissociation constant, Ka? I0.10 0 0 C-1.3 x 10-3+1.3 x 10-3 +1.3 x 10-3 E0.987 1.3 x 10-3 1.3 x 10-3

  8. Ka = 1.7 x 10-5 There are no units for the Ka value

  9. HA(aq) + H2O(l) H3O+(aq) + A¯(aq) HA is a weak acid with a Ka of 7.3 x 10-8. What are the equilibrium concentrations (HA, H3O+ and A¯) if the initial concentration of HA is 0.50 mol/L? I0.50 0 0 C-x+x +x E0.5-x +x +x

  10. *Ka is small - assume that x is negligible compared to 0.50

  11. [H3O+] = [A¯] = x = 1.9 x 10¯4 mol/L [HA] = 0.50 - x = 0.50 - 1.9 x 10¯4 = 0.49981 mol/L [HA] = 0.50 mol/L *Ka is small - assume that x is negligible compared to 0.50

  12. Calculate the pH of a 0.10 mol/L hydrogen sulfide solution. (Ka=1.0 x 10-7) H2S (aq) + H2O (l) H3O+(aq) + HS-(aq) I 0.10 0 0 C -x +x +x E 0.10 - x x x

  13. [H3O+] = x = 1.0 x 10-4 mol/L pH = -log [H3O+] = -log(1.0 x 10-4) pH = 4.00

  14. Each acid/base has K associated with it. Diprotic/triprotic acids lose their hydrogensone at a time - Each ionization reaction has separate Ka. H2SO4(aq) H+(aq) + HSO4¯(aq) HSO4¯ (aq) H+(aq) + SO4-2(aq) Sulfuric acid H2SO4 Ka1 Ka2

  15. Percent Dissociation The dissociation constants represent the acid / base degree of dissociation. Another way to describe the amount of dissociation is by percent dissociation.

  16. CH2O2H (aq) + H2O(l) H3O+(aq) + CH2O2¯(aq) Calculate the percent dissociation of a 0.100 M solution of formic acid (CH2OOH) if the hydronium ion concentration is 4.21 x 10-3 M.

  17. Calculate the Kb of hydrogen phosphate ion (HPO42¯) if a 0.25 mol/L solution of hydrogen phosphate is dissociated is 0.080%. HPO42¯ + H2O H2PO4¯ + OH¯ [OH-] = [H2PO4-] = 2.0 x 10-4 mol/L

  18. HPO42¯ + H2O H2PO4¯ + OH¯ [OH-] = [H2PO4-] = 2.0 x 10-4 mol/L

  19. The smaller the Ka or Kb, the weaker the acid / base • The percent dissociation also describes the amount of acid/base dissociated • The percent dissociated is calculated by

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