Acid base equilibria
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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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Acid base equilibria

Acid Base Equilibria

Chapter 16 part II


Write the dissociation reaction for the following

Write the Dissociation Reaction for the following:

  • A. HCl

  • B. Acetic Acid

  • C. Ammonium ion

  • D. C6H5NH4+

  • E. [Al(H2O)6]3+


Answers

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?


Acid strength

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.


Weak acids

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.


Vocabulary

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


Diprotic acids

Diprotic Acids

  • These have two acidic hydrogens.

  • H2SO4

  • H2S

  • Triprotic Acids

  • Have three acidic hydrogens.

  • H3PO4

  • H3P


Oxyacids

Oxyacids

  • Acids in which the acidic hydrogen is bound to oxygen.

  • H2SO4

  • Organic Acids aka

  • Carboxylic Acids are a type of oxyacid.


Oxyacids1

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.


Table describing acids

Table: Describing Acids


What are the strong acids

What are the strong Acids?

  • Hickle

  • Hibber

  • Hi

  • Hicolo

  • HeNo

  • He So Fine


Question

Question

  • What is the relative strength of these conjugate bases?

  • Weak: H2O, F-, Cl-, NO2-, CN-

  • Find the Ka and arrange.

  • KaAcid

  • 7.2 X 10-4HF

  • 4.0 X 10-4HNO2

  • 6.2X 10-10HCN


Answer

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.


Water

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.


Is water the only compound capable of auto ionization

Is water the only compound capable of auto-ionization?

  • No.

  • In Solution ammonia ionizes to form ammonium and hydroxide.


Kw of water

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-]


Kw is the ion product

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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