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Acid Base Equilibria

Acid Base Equilibria. Chapter 16 part II. Write the Dissociation Reaction for the following:. A. HCl B. Acetic Acid C. Ammonium ion D. C 6 H 5 NH 4 + E. [Al(H 2 O) 6 ] 3+. Answers. A. HCl  H + + Cl- B. HC 2 H 3 O 2  H + + C 2 H 3 O 2 - C. NH 4 +  H + + NH 3

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Acid Base Equilibria

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  1. Acid Base Equilibria Chapter 16 part II

  2. Write the Dissociation Reaction for the following: • A. HCl • B. Acetic Acid • C. Ammonium ion • D. C6H5NH4+ • E. [Al(H2O)6]3+

  3. Answers • A. HCl  H+ + Cl- • B. HC2H3O2  H+ + C2H3O2- • C. NH4+  H+ + NH3 • D. C6H5NH4+  H+ + C6H5NH3+ • E. [Al(H2O)6]3+ H++[Al(H2O)5 OH]2+ • What about their Ka?

  4. Acid Strength • Strength is defined by the equilibrium position of its ionization. • Strong acids almost completely dissociate. • That is because strong acids have WEAK conjugate bases that do not compete effectively for the H+ ion.

  5. Weak Acids • Weak acids do not completely dissociate. • In fact most of a weak acid remains completely intact in solution. • The minority of the weak acid ionizes. • The reason is that weak acids have STRONG conjugate bases that have high affinity for the proton. • The weaker the acid, the stronger the conjugate base.

  6. Vocabulary • Monoprotic acids • Have only one proton to donate. • They may have more than one hydrogen in the chemical formula, but only one is an acidic hydrogen. • HCl • HNO3 • HC2H3O2

  7. Diprotic Acids • These have two acidic hydrogens. • H2SO4 • H2S • Triprotic Acids • Have three acidic hydrogens. • H3PO4 • H3P

  8. Oxyacids • Acids in which the acidic hydrogen is bound to oxygen. • H2SO4 • Organic Acids aka • Carboxylic Acids are a type of oxyacid.

  9. Oxyacids • The –COOH group can share the negative charge between two oxygens as a resonance structure. These tend to be weak acids; they do not fully ionize.

  10. Table: Describing Acids

  11. What are the strong Acids? • Hickle • Hibber • Hi • Hicolo • HeNo • He So Fine

  12. Question • What is the relative strength of these conjugate bases? • Weak: H2O, F-, Cl-, NO2-, CN- • Find the Ka and arrange. • Ka Acid • 7.2 X 10-4 HF • 4.0 X 10-4 HNO2 • 6.2X 10-10 HCN

  13. Answer • H2O is a stronger base than the conjugate • base of a strong acid. • Therefore: • Weakest Cl- < H2O < F- < NO2- < CN- strongest • How did we pick the others? • Read the Ka.

  14. Water • Is a substance that can act as both an acid and base is called an amphoteric substance. • Not only is water an amphoteric substance, it can also auto-ionize. • It can ionize with itself to form a hydroxide ion and a hydronium ion.

  15. Is water the only compound capable of auto-ionization? • No. • In Solution ammonia ionizes to form ammonium and hydroxide.

  16. Kw of Water • From the auto-ionization expression of water we get the equilibrium constant expression. • 2 H2O  H3O+ + OH- • Kw= [H3O+ ][OH-] • Why not H2O? • Kw= [H+ ][OH-]

  17. Kw is the ion-product • Kw is aka dissociation constant of water • It has been found experimentally that at 25 °C, • [H+ ]=[OH-] and they both equal 1X10-7M • Since Kw= [H+ ][OH-] = [1X10-7M]2 • Then Kw = 1X 10-14.

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