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Understanding Water Ionization: Relationship between Hydronium and Hydroxide Ions

Explore the ionization of water and the equilibrium between hydronium and hydroxide ions. Learn about the ion product of water (Kw) and how it varies with temperature. Discover how the addition of strong acids and bases affects the equilibrium of water.

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Understanding Water Ionization: Relationship between Hydronium and Hydroxide Ions

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  1. ACIDS AND BASES Ionization of Water

  2. Describe the relationship between the hydronium and hydroxideionconcentrations in water • Include: the ion productof water, Kw Additional KEY Terms

  3. Water is amphoteric H+ HA + H2O(l) H3O+(aq) + A¯(aq) or B + H2O(l) BH+(aq) + OH¯(aq) H+

  4. Water particles collide - ions form • Water also dissociates into ions - self-ionization H2O(l) + H2O(l)H3O+(aq) + OH¯(aq) H2O(l) H+(aq) + OH¯(aq)

  5. Water reaches equilibrium with its ions ion product for water, Kw H2O(l) H+(aq) + OH¯(aq) KW = [H+][OH¯] KW = [H3O+][OH¯]

  6. At room temperature: Kw = [H+][OH-] = 1.00 x 10-14 Water is neutral - these ions must be a 1:1 ratio [H+] = [OH-] = 1.00 x 10-7 M Like all constants, the value of Kw varies with temperature.

  7. Like any reversible reaction, Le Chatelier's applies: OH- H+ + H2O Add a SB – increase [OH-] decrease [H+] Add a SA – increase [H+] decrease [OH-] This means that H+and OH¯ are BOTH present in any solution - whether they are acidic or basic. Kw = [H+][OH-] = 1.00 x 10-14

  8. n V 2.5 mol = 0.50 mol/L 5.0 L If 2.5 moles of hydrochloric acid is dissolved in 5.0 L of water, what is the [hydroxide ions]? HCl (s) H+(aq) + Cl¯(aq) M = Since HCl is a strong acid (100% dissociation): [H+] = 0.50 M

  9. How does the addition of HCl affect WATER’s equilibrium? Kw = [H3O+] [OH-] Amount contributed by self-ionization of water H2O(l) H+(aq) + OH¯(aq) 1.0 x 10-14 = [OH-] [0.50 ] + 1.0 x 10-7] [OH-] = 2.0 x 10-14 M

  10. 0.40 g of NaOH is dissolved in water to make a solution with a volume of 1.0 L. What is the hydronium ion concentration in this solution? NaOH (s) Na+(aq) + OH¯(aq) NaOH = 40.0 g/mol 0.40 g 1 mol = 0.010 M 1 L 40.0 g Since NaOH is a strong base(100% dissociation): [OH-] = 0.010 M

  11. How does addition of NaOH affect WATER’s equilibrium? Kw = [H3O+] [OH-] 1.0 x 10-14 = [H3O+] [0.010 ] + 1.0 x 10-7] [H+] = 1.0 x 10-12 M

  12. H2O(l) H+(aq) + OH¯(aq) KW = [H+][OH¯] = 1.00 x 10-14 Add a SA – increase [H+] decrease [OH-] Add a SB – increase [OH-] decrease [H+]

  13. CAN YOU / HAVE YOU? • Describe the relationship between the hydronium and hydroxideionconcentrations in water • Include: the ion productof water, Kw Additional KEY Terms

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