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Acids/Bases and Kw

Acids/Bases and Kw. Acid and Base Strengths. Taken from State University of West Georgia Chemistry Dept. Acid and Base Strengths. Taken from State University of West Georgia Chemistry Dept. Hydronium Ions. Hydronium Ions. H 5 O 2 +. Dissociation of Water.

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Acids/Bases and Kw

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  1. Acids/Bases and Kw

  2. Acid and Base Strengths • Taken from State University of West Georgia Chemistry Dept.

  3. Acid and Base Strengths • Taken from State University of West Georgia Chemistry Dept.

  4. Hydronium Ions

  5. Hydronium Ions H5O2+

  6. Dissociation of Water • H2O + H2O <---> H3O1+ + OH1- • The equilibrium expression is products over reactants. • K = [H3O1+] [OH1-] / [H2O] [H2O] • The molarity for the water is a constant at any specific temperature. So • K [H2O] [H2O] = [H3O1+] [OH1-] • The quantity on the right hand side of the equation is formally defined as Kw. The numerical vale for Kw is different at different temperatures. • At 25oC Kw = 1.014 x 10-14 • Kw = K[H2O] [H2O] or Kw = [H3O1+] [OH1-]

  7. Dissociation of Water • Equilibrium constants exist then for both acid dissociation and base. (Ka and Kb) • The higher the Ka, the stronger the acid and the higher the Kb, the stronger the base. • Ka and Kb are related by the previous equation. • Kw = KaKb

  8. Dissociation of Water • As Ka gets larger the strength of the acid gets higher, but Kb must fall.  Therefore the stronger the acid, the weaker the conjugate base.

  9. Dissociation of Water • It can now be said that the conjugate base (acid) of a weak acid (base) is a weak base (acid) and the conjugate base (acid) of a strong acid (base) is a worthless base (acid).

  10. Dissociation of Water • The strength of an acid/base is usually given as a pKa value. As pKa is inversely related to Ka, the higher the Ka (the stronger the acid), the lower the pKa value. The same is true of bases.

  11. Calculating pH -log [H+] Power of Hydronium (Hydrogen) P[OH-] = - log [OH]

  12. The pH Scale

  13. pH in Solutions of Strong Acids and Strong Bases • Strong acids • Certain acids are known as strong acids. These are acids that fully ionize when placed in water: • HA + H2O  A- + H3O+ • Goes to completion and thus • Ka = [A-][H3O+]/[HA] = infinity • Some common strong acids are: • HCl, hydrochloric acid • HBr, hyrdobromic acid • HI, hydroiodic acid • H2SO4, sulfuric acid • HNO3, nitric acid • HClO4, perchloric acid

  14. pH in Solutions of Strong Acids and Strong Bases • Strong Bases • Certain bases are known as strong bases. These are bases that fully ionize when placed in water. • Some common strong bases are: • LiOH, lithium hydroxide • NaOH, sodium hydroxide • KOH, potassium hydroxide • Ca(OH)2, calcium hydroxide • Sr(OH)2, strontium hydroxide • Ba(OH)2, barium hydroxide • Alkaline earth oxides. • Lime (CaO)

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