Transcript 5/26 up to date

Chapter 15:
Acids and Bases
“K” Chemistry
(part 3 of 3)
Properties of Acids
• A sour taste
• Dissolves many metals
• Turns blue Litmus paper
red
• Neutralizes bases
• Liberate the H+ ion
– Reacts to form hydronium
– H3O+
• A STRONG ACID will
dissociate 100%
– What is HF not a strong acid??
Six Strong Acids
1.
2.
3.
4.
5.
6.
Properties of Bases
•
•
•
•
•
A bitter taste
Feel slippery to the touch
Turn red Litmus paper blue
The ability to neutralize acids
Associated with the OH- anion
• What would be a strong base??
– Hint: Think about your solubility rules
Bases
• Bases feel slippery because they react with
the oils on the skin to form a soap-like
substance
• It is for this reason that bases are used as
cleaning agents around the house
Definitions of Acids and Bases
• Three different working definitions of acids and
bases:
– Arrhenius
– Brᴓnsted-Lowry
– Lewis
• Why Have three?? Which is correct??
– Different definitions are convenient at different times
and in different scenarios… no one perfect definition
The Arrhenius Definition
• Acid: A substance that produces H+ ions in
aqueous solution
HCl(aq)  H+(aq) + Cl-(aq)
– HCl is an acid because it produces H+ ions
• Base: a substance that produces OH- ions in
aqueous solution
NaOH(aq)  Na+(aq) + OH-(aq)
– NaOH dissociate completely and produced the
hydroxide ion
Arrhenius Acids
HCl(aq)  H+(aq) + Cl-(aq)
• Consider the acid… the H+ is aqueous
– It continues and reacts with H2O to yield the
hydronium ion
H+(aq) + H2O(l)  H3O+(aq)
Acids and Bases
HCl(aq)  H+(aq) + Cl-(aq)
NaOH(aq)  Na+(aq) + OH-(aq)
Under the Arrhenius Definition, acids and bases
readily and naturally come together to form water:
H+(aq) + OH-(aq)  H2O(l)
Think way back… what does the reaction represent?
The Brᴓnsted-Lowry Definition
• Acid: A proton (H+ ion) donor
• Base: A proton (H+ ion) acceptor
• Again, HCl is an acid by this definition
HCl(aq) + H2O(l)  H3O+(aq) + Cl-(aq)
– The acid donates the proton to the water… HCl is
an acid here… Water is _______________
Brᴓnsted-Lowry Base
• Think about ammonia…
NH3(aq) + H2O(l)  NH4+(aq) + OH-(aq)
There is no OH- to be liberated from NH3
(Arrhenius Definition), however, it does “accept
a proton” from the water, making it a BrᴓnstedLowry Base!!
Amphoteric
• HCl(aq) + H2O(l)  H3O+(aq) + Cl-(aq)
• NH3(aq) + H2O(l)
NH4+(aq) + OH-(aq)
• Water plays a couple different roles here…
– Water can be an acid OR a base depending on who is
around… this trait is called Amphoteric
Conjugate Acid-Base Pairs
NH3(aq) + H2O(l)
NH4+(aq) + OH-(aq)
• In the reverse rxn, the NH4+ (acid) is the proton
donor and the OH- is the proton accepter (base)
• NH4+ and NH3 are known as a conjugate acidbase pair
– Two substances related to each other by the transfer
of a proton
Conjugate Pairs
NH3(aq) + H2O(l)
Base
Acid
NH4+(aq) + OH-(aq)
Conjugate
Acid
Conjugate
Base
• In an Acid-Base Reaction,
– A base accepts a proton and becomes a conjugate
acid
– An acid donates a proton and becomes the
conjugate base
Practice
• Identify the Bronsted-Lowry acid, the
Bronsted-Lowry base, the conjugate acid, and
the conjugate base
(a) H2SO4(aq) + H2O(l)  HSO4-(aq) + H3O+(aq)
(b) HCO3-(aq) + H2O(l)
H2CO3(aq) + OH-(aq)
More Practice
• Identify the Bronsted-Lowry acid, the
Bronsted-Lowry base, the conjugate acid, and
the conjugate base
(a) C5H5N(aq) + H2O(l)
C5H5NH+(aq) + OH-(aq)
(b) HNO3(aq) + H2O(l)  H3O+(aq) + NO3-(aq)
Acids
• Monoprotic Acids – containing only one
ionizable proton
• Diprotic Acids – an acid containing two
ionizable protons
– Polyprotic
Acid Ionization Constant (Ka) 
• A Strong Acid dissociates COMPLETELY,
whereas a weak acid only partially ionizes
• The amount the acid ionizes (regarding weak
acids, not 100%) determines its strength
– The “strength of weak acids” – not applicable to
SA – they dissociate completely
Acid Ionization Constant (Ka)
HA(aq) + H2O(l)
H3O+(aq) + A-(aq)
Keq = [prod]/[react] = Ka
• If the equilibrium lies far to the right, the acid is strong
(more dissociation)
• If the equilibrium lies far to the left, the acid is weak
(only a small percentage of the acid molecules are
ionized)
Strength of Acids
• The amount ionized is a clear indicator of the strength
of an acid (SA completely…)
• The Ka is a direct measure of where this equilibrium lies
• SA will have no reactants in the Ka (completion
reaction) – what does this mean about the magnitude
of the Ka?
• WA will have a large quantity of reactants… what does
this mean?
• Left off on page 671
• Refer to equations and notes on board…
• Additionally, read through the pH scale and
the concentration calculations through the
remaining sections of the chapter
Titrations
• Titrations –
• Buret –
• End Point –
• Equilibrium Point –
• Indicator Solution –
• Dilutions –