ACIDS AND BASES Ionization of Water H O H H + O H -

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    29-Mar-2015

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ACIDS AND BASES Ionization of Water H O H H + O H - Slide 2 Describe the equilibrium between hydronium and hydroxide ions in water. Define the ion product of water (K w ). Describe the concentrations of hydronium and hydoxide ions. Calculate the concentration of hydronium or hydroxide ions. Slide 3 Water is amphoteric HA + H 2 O (l) H 3 O + (aq) + A (aq) or B + H 2 O (l) BH + (aq) + OH (aq) Slide 4 Water dissociates into ions - self-ionization. When water particles collide - ions form. H 2 O (l) H + (aq) + OH (aq) H 2 O (l) + H 2 O (l) H 3 O + (aq) + OH (aq) or Slide 5 ion product for water, K w K W = [H 3 O + ][OH] K W = [H + ][OH] H 2 O (l) H + (aq) + OH (aq) Slide 6 In room temperature water, the concentration of hydrogen ions and hydroxide ions, are each 1.0 x 10 -7 mol/L Water is neutral - these two must be a 1:1 ratio Any solution in which the [H + ] and [OH - ] are 1.0 x 10 -7 M is described as a neutral solution. Like all eqbm constants, the value of K w varies with temperature. K w = [H + ][OH - ] = 1.00 x 10 -14 Slide 7 Like any reversible reaction, Le Chatelier's applies: 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. OH - H2OH2O H+H+ + Slide 8 If 2.5 moles of hydrochloric acid is dissolved in 5.0 L of water, what is the concentration of the hydroxide ions? Since HCl is a strong acid (100% dissociation): [H 3 O + ] = 0.50 mol/L. 5.0 L = 0.50 mol/L 2.5 mol n V M= HCl (s) H + (aq) + Cl (aq) Slide 9 [OH - ] = 2.0 x 10 -14 M K w = [H 3 O + ] [OH - ] 1.0 x 10 -14 = [0.50 [OH - ] + 1.0 x 10 -7 ]] Slide 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 = 40.0 g/mol 0.40 g 1 L 40.0 g 1 mol = 0.01 mol/L NaOH (s) Na + (aq) + OH (aq) Slide 11 [NaOH] = [OH ] = 0.010 mol/L Substitute into the equilibrium law and solve for hydronium ion concentration: [H + ] = 1.0 x 10 -12 M K w = [OH - ] [H 3 O + ] 1.0 x 10 -14 = [0.010 [H 3 O + ] + 1.0 x 10 -7 ]] Slide 12 H 2 O (l) H + (aq) + OH (aq) K W = [H + ][OH] = 1.00 x 10 -14 Add a SA increase [H + ] decrease [OH - ] Add a SB increase [OH - ] decrease [H + ]

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