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### Understanding Bases in Aqueous Solutions: Reactions, Equations, and pH Calculations ####

Explore the role of bases in aqueous solutions using Arrhenius and Bronsted-Lowry definitions. Learn about strong bases like NaOH, KOH, and weak bases such as ammonia. Understand base equations and calculations for pH, pOH, [H+], and [OH-]. See examples with Ba(OH)2 and methylamine. ####

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### Understanding Bases in Aqueous Solutions: Reactions, Equations, and pH Calculations ####

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  1. Bases Definitions Arrhenius : Bases produce hydroxide ions in aqueous solutions Bronsted - Lowry: Bases accept hydrogen ions

  2. Reactions of Bases in Aqueous Solutions Strong Bases - Group 1 and 2 metal hydroxides NaOH, KOH, LiOH, Ca(OH)2, Ba(OH)2, Sr(OH)2 Kb is very large, not measureable MOH is 100% dissociated OH+- is approximately MOH initial

  3. Weak Bases - ammonia amines - nitrogen containing organic compounds Base Equation: B + HOH BH+ + OH - NH3 + HOH  NH4+ + OH - Kb = [BH+] [OH -] B Kb is much less than 1 Dissociation is reactant favored OH - is much less than B initial

  4. Determine the pH, pOH, [H +], and [OH -] of a 0.0015 M solution of barium hydroxide Ba(OH)2 is a strong base and 100% dissociated Ba(OH)2  Ba 2+ + 2 OH - OH - = 2 (0.0015) = 0.003 M pOH = - log (0.003) = 2.52 pH = 14 - 2.52 = 11.48 H + = log ( - 11.5) = 3.1 x 10 - 12 M

  5. Determine the pH, pOH, [H + ], and [OH - ] of a 1.0 M solution of methylamine (CH3NH2) if the Kb of methylamine is4.38 x 10 -4 CH3NH2 + HOH  CH3NH3+ + OH - Kb = 4.38 x 10 -4 = [CH3NH3+] [OH -] [CH3NH2 ] CH3NH2 + HOH  CH3NH3+ + OH - Initial (M) 1.0 0 0 Change (M) -x x x Equil (M) 1.0 - x x x 4.38 x 10 -4 = (x) (x) pOH = 1.68 1.0 pH = 12.32 x = 0.021 M = [OH -] [H +] = 4.79 x 10 -13 M

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