Acid Base Equilibria Chapter 16 part II Write

Acid Base Equilibria Chapter 16 part II

Write the Dissociation Reaction for the following: n n n A. HCl B. Acetic Acid C. Ammonium ion D. C 6 H 5 NH 4+ E. [Al(H 2 O)6]3+

Answers n n n A. HCl H+ + Cl. B. HC 2 H 3 O 2 H+ + C 2 H 3 O 2 C. NH 4+ H+ + NH 3 D. C 6 H 5 NH 4+ H+ + C 6 H 5 NH 3+ E. [Al(H 2 O)6]3+ H+ + [Al(H 2 O)5 OH]2+ What about their Ka?

Acid Strength n n n 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.

Weak Acids n n n 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.

Vocabulary n n n 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 HNO 3 HC 2 H 3 O 2

Diprotic Acids n n n n These have two acidic hydrogens. H 2 SO 4 H 2 S Triprotic Acids Have three acidic hydrogens. H 3 PO 4 H 3 P

Oxyacids n n Acids in which the acidic hydrogen is bound to oxygen. H 2 SO 4 Organic Acids aka Carboxylic Acids are a type of oxyacid.

Oxyacids n 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.

Table: Describing Acids Strong Weak Ka Value Large small Equilibrium position Equilibrium [H+] to [HA] Strength of conjugate base Far to right Far to left [H+]>>[HA] [H+]<<[HA] Weak A- is weaker than H 2 O Strong A- is stronger than H 2 O

What are the strong Acids? n n n Hickle Hibber Hi Hicolo He. No He So Fine

Question n n n What is the relative strength of these conjugate bases? Weak: H 2 O, F-, Cl-, NO 2 -, CNFind the Ka and arrange. Ka Acid 7. 2 X 10 -4 HF 4. 0 X 10 -4 HNO 2 6. 2 X 10 -10 HCN

Answer n n n H 2 O is a stronger base than the conjugate base of a strong acid. Therefore: Weakest Cl- < H 2 O < F- < NO 2 - < CN- strongest How did we pick the others? Read the Ka.

Water n n n 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.

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

Kw of Water n n n From the autoionization expression of water we get the equilibrium constant expression. 2 H 2 O H 3 O+ + OHKw= [H 3 O+ ][OH-] Why not H 2 O? Kw= [H+ ][OH-]

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