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ACIDS AND BASES

ACIDS AND BASES. Ionization of Water. CAN YOU / HAVE YOU? Describe equilibrium between hydronium and hydroxide ions in water. Define the ion product of water (K w ). Calculate the concentration of hydronium or hydroxide ions. Water is amphoteric.

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ACIDS AND BASES

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  1. ACIDS AND BASES Ionization of Water

  2. CAN YOU / HAVE YOU? • Describe equilibrium between hydronium and hydroxide ions in water. • Define the ion product of water (Kw). • Calculate the concentration of hydronium or hydroxide ions.

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

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

  5. ion product for water, Kw KW = [H+][OH¯] H2O(l) H+(aq) + OH¯(aq) KW = [H3O+][OH¯]

  6. In room temperature water, the concentration of hydrogen ions and hydroxide ions, are each 1.0 x 10 -7mol/L Water is neutral - these two must be a 1:1 ratio [H+] = [OH-] = 1.00 x 10-7 Kw = [H+][OH-] = 1.00 x 10-14 Like all eqbm constants, the value of Kw varies with temperature.

  7. Like any reversible reaction, Le Chatelier's applies: OH- H+ + H2O Add a SA – increase [H+] decrease [OH-] Add a SB – increase [OH-] decrease [H+] 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 concentration of the hydroxide ions? HCl (s) H+(aq) + Cl¯(aq) M = Since HCl is a strong acid (100% dissociation): [H3O+] = 0.50 mol/L.

  9. Kw = [H3O+] [OH-] 1.0 x 10-14 = [OH-] H2O(l) H+(aq) + OH¯(aq) [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 = 0.01 mol/L 1 L 40.0 g

  11. [NaOH] = [OH–] = 0.010 mol/L Substitute into the equilibrium law and solve for hydronium ion concentration: 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 equilibrium between hydronium and hydroxide ions in water. • Define the ion product of water (Kw). • Calculate the concentration of hydronium or hydroxide ions.

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