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A CIDS /B ASES AND K W. A CID AND B ASE S TRENGTHS Taken from State University of West Georgia Chemistry Dept.

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Presentation on theme: "A CIDS /B ASES AND K W. A CID AND B ASE S TRENGTHS Taken from State University of West Georgia Chemistry Dept."— Presentation transcript:

1 A CIDS /B ASES AND K W

2 A CID AND B ASE S TRENGTHS Taken from State University of West Georgia Chemistry Dept.

3 A CID AND B ASE S TRENGTHS Taken from State University of West Georgia Chemistry Dept.

4 H YDRONIUM I ONS

5 H5O2+H5O2+

6 D ISSOCIATION OF W ATER H 2 O + H 2 O H 3 O 1+ + OH 1- The equilibrium expression is products over reactants. K = [H 3 O 1+ ] [OH 1- ] / [H 2 O] [H 2 O] The molarity for the water is a constant at any specific temperature. So K [H 2 O] [H 2 O] = [H 3 O 1+ ] [OH 1- ] 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 = x Kw = K[H 2 O] [H 2 O] or Kw = [H 3 O 1+ ] [OH 1- ]

7 D ISSOCIATION OF W ATER Equilibrium constants exist then for both acid dissociation and base. (K a and K b ) The higher the K a, the stronger the acid and the higher the K b, the stronger the base. K a and K b are related by the previous equation. K w = K a K b

8 D ISSOCIATION OF W ATER As K a gets larger the strength of the acid gets higher, but K b must fall. Therefore the stronger the acid, the weaker the conjugate base.

9 D ISSOCIATION OF W ATER 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 D ISSOCIATION OF W ATER The strength of an acid/base is usually given as a pK a value. As pK a is inversely related to K a, the higher the K a (the stronger the acid), the lower the pKa value. The same is true of bases.

11 C ALCULATING P H -log [H+] Power of Hydronium (Hydrogen) P[OH-] = - log [OH]

12 T HE P H S CALE

13

14 P H IN S OLUTIONS OF S TRONG A CIDS AND S TRONG B ASES Strong acids Certain acids are known as strong acids. These are acids that fully ionize when placed in water: HA + H 2 O  A - + H 3 O + Goes to completion and thus Ka = [A-][H3O+]/[HA] = infinity Some common strong acids are: HCl, hydrochloric acid HBr, hyrdobromic acid HI, hydroiodic acid H 2 SO 4, sulfuric acid HNO 3, nitric acid HClO 4, perchloric acid

15 P H IN S OLUTIONS OF S TRONG A CIDS AND S TRONG B ASES 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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