acids bases and titrations

7/28/2019 Acids Bases and Titrations

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Aqueous Acid-BaseEquilibria and

Titrations

Chapter 14

Sections 14.1 14.7

Chapter 15

Section 15.3


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Acid and Base

Theories Arrhenius Theory 1884

Assumes all acids have H+ and allbases have OH- (problem)

Strong electrolytes dissociate

completely upon dissolving Weak electrolytes dissociate partly

upon dissolving

Neutralization makes water(problem)

Brnsted-Lowry Theory 1923 Acids are proton (p+ or H+) donors

and bases are proton acceptors

Neutralization may make water orsalts

Lewis Theory Lewis acids accept an electron pair

via an empty orbital whereas Lewisbases donate an electron pair


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Brnsted-Lowry

Theory Conjugate acid acid formed by the addition

of a proton to a base

Conjugate base base formed by the removalof a proton from an acid

Conjugate pair set of base andcorresponding conjugate acid or the set of acidand corresponding conjugate base

Amphiprotic compound that may accept ordonate a proton, i.e. may be an acid or a base

Polyprotic compound that may donate more

than one proton per molecule Monoprotic compound that is capable of only

donating (or accepting) 1 proton per molecule

(Practice) Example:


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Ionization

Strong acids and bases ionize ordissociate completely

Weak acids and bases ionize/dissociatepartially Are at equilibrium, favoured side based on

relative strengths Acid ionization constant (Ka)

Base ionization constant (Kb)

Water may self-ionize/autoionize Ion product of water (Kw)

Hydronium ion = H3O+ = essentially the

same thing as H+

Kw = [H3O+][OH-] = 1.0 x 10-14 M at 25oC

Kw = (Ka)(Kb)

b

w

a

K

K

HA

HAK ==

+

][

]][[

a

w

b

K

K

B

OHBHK ==

+

][

]][[

(Practice) Examples:

Section Exercises:


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pH Method of describing [H3O

+]

potential of hydrogen ion

pH = - log[H3O+]

[H3O+] = 10-pH

pOH = - log[OH-] [OH-] = 10-pOH

pK = - logK K = 10-pK

pKw = pH + pOH = 14.00

pH, pOH, pK(Practice) Examples:

Section Exercises:


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Percent Hydrolysis and

Salts Percent ionization or percent

dissociation or percent hydroylsis

Strong acids/bases are 100% ionized

Weak acids/bases have increased ionizationat lower concentrations

Salts

Strong acid + strong base no pH effect

Strong acid + weak base

acidic effect Weak acid + strong base basic effect

Weak acid + weak base depends on Kaand Kb

%100][

][% 3

HA

OHionization

+

=

(Practice) Examples:Section Exercises:Table:


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Structure and Recognition

Molecular structure relationshipto strength Oxyacids

Carboxyic acids

Binary acids

Amines Zwitterions


Tables:

Section Exercises:


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Neutralization

Reactions andTitration Curves

Titration Curve Plot of pH vs amount of titrant added

Titrant The solution that is added to the beaker

where the neutralization reaction takesplace/has indicator

End Point

When the indicator changes colour Equivalence or Stoichiometric point

When the stoiciometric amount (in mol) ofacid is the same as the amount of base(neither are in excess)

Mid Point

When the amount (in mol) of titrant is that of the solution

Also known as the half equivalence point


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Neutralization


Indicators Display colour changes with different pHs

Very little is required and used

Need ~90% in the acid or base form to getthat colour and may have intermediatecolours

May be prepared as a paper or as asolution

Is approximate pH

Standardization To find the solution concentration by the

use of another solution with a knownconcentration


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Neutralization


Strong acid + Strong base Drastic change in pH at the equivalence

point

Weak acid + Strong base Has an acidic buffer region with a less

drastic change in pH at the equivalencepoint

Weak acid + Weak base Has an acidic buffer region and a basic

buffer region and is difficult to identify theequivalence point

Weak polyprotic acid + Strong base Has multiple acidic buffer regions and more

than one equivalence point


Figures:

Section Exercises:

acids bases and titrations

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