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Hydronium Ions and Hydroxide Ions

Hydronium Ions and Hydroxide Ions. Solutions Unit: Chapter 16. I. Self-Ionization of Water. Self-Ionization of Water – two water molecules produce a hydronium ion and a hydroxide ion by transfer of a proton. Equation: H 2 O (l) + H 2 O (l)  H 3 O + (aq) + OH - (aq)

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Hydronium Ions and Hydroxide Ions

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  1. Hydronium Ions and Hydroxide Ions Solutions Unit: Chapter 16

  2. I. Self-Ionization of Water • Self-Ionization of Water – two water molecules produce a hydronium ion and a hydroxide ion by transfer of a proton. • Equation: H2O (l) + H2O (l)  H3O+(aq) + OH-(aq) • Ionization Constant of Water, Kw • The product of [H3O+] and [OH-] remains constant in water and dilute aqueous solution at a constant temp. • Equation: Kw= [H3O+][OH-] = 1.0 x 10-14M2

  3. H2O + H2O  H3O+ + OH- I. Self-Ionization of Water Kw = [H3O+][OH-] = 1.0  10-14

  4. II. Neutral, Acidic and Basic Solutions • Neutral: [H3O+] and [OH-] are equal • Acidic: [H3O+] and [OH-] are not equal, [H3O+] is greater than [OH-] • Basic: [H3O+] and [OH-] are not equal, [OH-] is greater than [H3O+]

  5. III. [H3O+] and [OH-] Concentration Calc. • Need to recall that strong acid and bases are considered to be completely ionized or dissociated in weak aqueous solutions. • Steps of calculating concentrations: • Determine molarity of [H3O+] by using the concentration of the solution and the mole ratio of the equation. • Determine molarity of [OH-] using Kwformula solving for [OH-].

  6. III. [H3O+] and [OH-] Concentration Calc. • Example: What are the [H3O+] and [OH-] Concentration in a solution of 0.025 M HCl? • Given: 0.025 M HCl Unknown: [H3O+] and [OH-] • HCl (aq) + H2O (l) → H3O+ (aq) + Cl- (aq) Assuming 100% ionization 1. molarity of HCl = mol HCl/ L sol’n  mol HCl/L sol’n x 1 mol H3O+/1 mol HCl = mol H3O+/L sol’n = molarity HCl 0.025 mol HCl/L sol’n x 1 mol H3O+/1 mol HCl = 0.025 mol H3O+/L sol’n = 0.025 M H3O+ 2. [H3O+][OH-] = 1.0 x 10-14 M2 [OH-] = 1.0 x 10-14 M2 /[H3O+] [OH-] = 1.0 x 10-14 M2 /[0.025 M] = 4.0 x 10-13 M

  7. III. [H3O+] and [OH-] Concentration Calc. • Find the hydroxide ion concentration of 3.0  10-2 M HCl. Is it acidic or basic? • Given: 3.0  10-2 M HCl Unknown: [OH-] = ??? 2.[H3O+] = 3.0 10-2 M [H3O+][OH-] = 1.0  10-14 M2 [OH-] = 1.0  10-14 M2/ [3.0  10-2 M] [OH-] = 3.3  10-13 M 3. It is acidic because the [H3O+] [OH-].

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