AP Chemistry
Chapter 14 Sections 14.1 – 14.2 Note Organizer
The Nature of Acids and Bases and Acid Strength
Importance of Acids and Bases
•
•
•
•
Biological systems
They help control _________ of our ________ since deviations can result in illness or death.
Industry
For example, the vast quantity of _________ acid produced in the US is needed to
__________ fertilizers, polymers, steel, and many other materials.
The Nature of Acids and Bases
• _________: taste ______
• Citric acid is responsible for the sour taste of a lemon.
• _________ (sometimes called alkalis): taste _________ and feel ___________
• Commercial preparations for unclogging drains are highly basic.
• Based on experimentation, Svante Arrhenius postulated that ________ produce ___________
ions in aqueous solution, while ___________ produce _______________ ions.
• This is known as the _____________ concept of acids and bases.
• A more general concept was proposed by Johannes Brønsted and Thomas Lowry.
• In the ___________-_________ model, an ________ is a _________ (H+) _________, and a
________ is a __________ (H+) ______________.
• For example, when gaseous HCl dissolves in water, each ______ molecule __________ a
___________ to a water molecule and so qualifies as a Brønsted-Lowry acid.
• The molecule that __________ the ____________, is a Brønsted-Lowry _______ (H2O).
• Note the proton is transferred from the HCl molecule to the water molecule to form H3O+,
which is called the _______________ ion.
• The ___________ ______________ that occurs when an acid is dissolved in water can be
represented as
•
HA(aq) + H2O(l) ⇌ H3O+(aq) + A-(aq)
• A __________ _______-_______ pair consists of two substances related to each other by the
___________ and ____________ of a single proton.
• Above there are two conjugate acid-base pairs:
•
HA and AH2O and H3O+
• Important!!
•
HA(aq) + H2O(l) ⇌ H3O+(aq) + A-(aq)
• In the reaction there is a ____________ between the two _________, H2O and A-, for the
____________.
• If ______ is a ____________ base than A-, the _____________ lies far to the ________
(most of HA will be ionized at equilibrium).
• If _____ is a ____________ base than H2O, the equilibrium lies far to the _______ (most of
HA at equilibrium still HA).
• HA(aq) + H2O(l) ⇌ H3O+(aq) + A-(aq)
• The ____________ _______________ for the reaction can be written as:
Ka =
•
•
•
[H3O + ][ A ] [H+ ][ A ]
=
[HA]
[HA]
_____ is called the ________ ______________ constant.
Note H3O+ or H+ can be used to represent the __________ __________ (in water). We will
use H+ henceforth.
Note _____ (l) is ___________ in the equilibrium expression; therefore, we can write:
•
•
•
•
•
HA(aq) ⇌ H+(aq) + A-(aq)
Even though we omit water don’t forget that ________ plays an ____________ role in
causing the acid to ___________.
Note that Ka is the equilibrium constant for the __________ in which a ________ is
___________ from HA to form the conjugate base A-.
We use Ka to represent only this type of reaction.
Knowing this, you can write the Ka expression for any acid, even one that is totally
unfamiliar to you.
Acid Strength
• The __________ of an _______ is determined by the _______________ ____________ of its
dissociation (ionization) reaction:
•
HA(aq) + H2O(l) ⇌ H3O+(aq) + A-(aq)
• ___________ Acid = equilibrium lies far to the _________.
• ___________ Acid = equilibrium lies far to the _________.
• A _________ acid yields a _______ ____________ _________ – one that has a low affinity
for a proton.
• A ________ acid yields a _________ _____________ ________ – one that has a high
affinity for a proton.
• The _____________ _________ acids are sulfuric acid [H2SO4(aq)], hydrochloric acid
[HCl(aq)], nitric acid [HNO3(aq)], perchloric acid [HClO4(aq)], hydrobromic acid [HBr
(aq)], and hydroiodic acid [HI (aq)].
• __________ acid is a ____________ acid – has ______ acidic ____________.
• The table (See table 14.2) below lists common monoprotic acids (one acidic proton) and their
Ka values.
• Note the strong acids are not listed. Their equilibrium lies so far to the right Ka cannot be
correctly determined.
• Most acids are ____________, in which the acidic ___________ is attached to an _________
atom.
• Organic acids, those with a __________ atom ___________, commonly contain the
___________ group.
• Acids of this type are usually weak.
• Examples are acetic acid (HC2H3O2) and benzoic acid (HC7 H5O2).
• The acidic proton is written in the front.
• The remainder of the hydrogens are not acidic – they do not form H+ in water.
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Water as an Acid and a Base
A substance is _____________ is it can behave __________ as an _______ or as a
________.
___________ is the most common amphoteric substance.
This is seen in the ________________ of water below.
H2O +
H2O ⇌
H3O+ + OHacid(1) base(1)
acid(2)
base(2)
This reaction gives the following ______________ expression:
Kw = [H3O+][OH-] = [H+][OH-]
Kw = _____-____________ constant or ______________ constant for water.
Experiment shows that at 25oC in _________ water,
[H+] = [OH-] = 1.0 x 10-7 M
which means that at 25oC
Kw = [H+][OH-] = (1.0 x 10-7)(1.0 x 10-7)
= 1.0 x 10-14
In any ____________ solution at 25oC, no matter what is contains, the ____________ of
[H+] and [OH-] must always ____________ 1.0 x 10-14.
Kw = [H+][OH-] = (1.0 x 10-7)(1.0 x 10-7)
•
•
•
•
•
•
= 1.0 x 10-14
This leads to three possible situations:
A ____________ solution, where [H+] = [OH-].
An ___________ solution, where [H+] > [OH-].
A ____________ solution, where [OH-] > [H+].
Remember the product of [H+][OH-] must equal 1.0 x 10-14.