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Ionization constant, K a, for a weak acid

Ionization constant, K a, for a weak acid. HA D H + + A - K a = [H + ][A - ] [HA]. What is the [H + ] in 0.100M formic acid? K a for formic acid is 1.77 x 10 -4 HCOOH D H + + COOH -

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Ionization constant, K a, for a weak acid

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  1. Ionization constant, Ka, for a weak acid HA D H+ + A- Ka = [H+][A-] [HA]

  2. What is the [H+] in 0.100M formic acid? Ka for formic acid is 1.77 x 10-4 HCOOH D H+ + COOH- Since this is a weak acid, [HCOOH] ͌ 0.100M Ka = [H+][COOH-]= 1.77 x 10-4 [HCOOH] Let x = [H+] = [COOH-] x2= 1.77 x 10-4 0.100 X = 4.21 x 10-3M

  3. Percent ionization [amount ionized] [original acid] What is the percent ionization of [H+] from the previous problem? [H+] = 4.21 x 10-3M, [HCOOH] = 0.100M 4.21 x 10-3= 4.21% 0.100

  4. Kb • base-dissociation constant NH3(aq) + H2O(l) NH4+(aq) + OH-(aq) Kb = [NH4+][OH-] [NH3] • if Kb is large, the products of the dissociation reaction are favored • if Kb is small, undissociated base is favored.

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