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It shouldn't be hard for you to name several
common acids, but you might find that listing
bases is just a little more difficult.
Here's a partial list of some common acids
and bases, along with some chemical
formulas:
Some Common Acids
Some Common Bases
hydrochloric acid, HCl
(stomach acid)
sodium hydroxide, NaOH
(lye or caustic soda)
sulfuric acid, H2SO4
potassium hydroxide, KOH
(lye or caustic potash)
nitric acid, HNO3
(milk of magnesia)
magnesium hydroxide, Mg(OH)2
carbonic acid, H2CO3
acetic acid, HC2H3O2 (vinegar)
formic acid, HCOOH
calcium hydroxide, Ca(OH)2
(slaked lime)
citric acid, C6H8O7
ammonia, NH3
acetylsalicylic acid, commonly known as
aspirin
C6H4(OCOCH3)CO2H
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Acids and bases have characteristic
properties. You'll want to learn this list.
Key Characteristics of Acids
sour taste (e.g. lemons; vinegar;
sour milk)grapefruit;
react with active metals such as
zinc and magnesium to produce
hydrogen gas
form electrolytic solutions
(conduct electricity) because they
produce ions
cause certain dyes to change
color; litmus paper turns red, for
example
Key Characteristics of Bases
bitter taste
generally no noticeable reaction
with active metals
form electrolytic solutions
(conduct electricity) because they
produce ions
cause certain dyes to change
color; litmus paper turns blue for
example
slippery feel (e.g. soapy feel)
neutralized by bases
neutralized by acids
(neutralized means that the
substance no longer has acidic, or
basic, properties)
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Acids all have one thing in common, and
most bases have another
the properties of acids were due to the
presence of hydrogen ions, H+, and
the properties of bases were due to the
presence of hydroxide ions, OH-.
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An important aspect is that these compounds
only become acid or bases when in solution.
We need to examine what happens when we
add them to water that suddenly produces
either acidic or basic properties.
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Lab 5.1.2
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Recall: electrolytic solutions are those that
conduct electricity because the substance
dissolves in water to produce ions.
Solutions that conduct electricity well are
strong electrolytes –because they break
down well and produce many ions in solution.
Weak electrolytes do not conduct electricity
and have fewer ions are produced in solution.
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Ionic compounds and some molecular
compounds can produce electrolytic
solutions, in a process called dissociation
Dissociation of ionic compounds occurs when
water molecules “pull apart” the ionic crystal
because of strong attractions between the
polar ends of the water molecule and the
positive and negative ions within the crystal.
Water molecules then surround the cations
and anions; called hydration
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NaCl(s) → Na+(aq) + Cl-(aq)
Na2SO4 (s) → 2 Na+(aq) + SO42-(aq)
(NH4)3PO4 (s) → 3 NH4+(aq) + PO43-(aq)
NaOH(s) → Na+(aq) + OH– (aq)
KOH(s) → K+(aq) + OH– (aq)
Mg(OH)2 (s) → Mg2+(aq) + 2 OH– (aq)
all three of the last reactions produce
hydroxide ions, OH– and are Arrhrenius bases
since they produce hydroxide ions in solution.
There are two important things to notice
about writing dissociation equations:
1. Generally DO NOT include H2O as a
reactant. There are some exceptions to this
rule.
2. Ion charges MUST BE included!
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An ion, such as the sodium ion Na+ is not the
same as a sodium atom, Na. Refer to your
Table of Common Ions if needed.
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When molecular compounds dissolve in
water to produce ions the process is typically
called ionization.
Recall that molecular compounds are held
together by covalent bonding;
ionic compounds are held together by ionic
bonding
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Most molecular compounds do not undergo
ionization. Acids are an exception. All acids produce
hydrogen ions in solution. Some examples:
HCl (g)→ H+(aq) + Cl-(aq)
H2SO4 (g)→ 2 H+(aq) + SO42-(aq)
These are actually simplified versions of the actual
equations:
HCl(g) + H2O(l) → H3O+(aq) + Cl-(aq)
H2SO4 (g) + H2O(l)→ 2 H3O+(aq) + SO42-(aq)
it won't make a difference which way you write the
reactions, for our purposes they will represent the
same thing.
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Note: an Arrhenius base was defined as a
substance that produces hydroxide ions in
solution. But remember ammonia, NH3????
How can it be a base? It is a general theory
that has some exceptions such as ammonia
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That lack of an OH- group in ammonia is a bit
of a problem at first glance, but let's take a
closer look at what happens when NH3 is
added to water:
NH3 (g) + H2O(l)
NH4+(aq) + OH–(aq)
This is known as the Brønsted-Lowry theory
of acids and bases can be stated as follows:
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Acids are substances that
produce a hydrogen ion
(or a proton donor)
Bases are substances that can
accept a hydrogen ion
(or a proton acceptor)
Using hydrochloric acid as an example, consider
how HCl acts as an acid:
 HCl (g)→ H+(aq) + Cl-(aq)
or
 HCl(g) + H2O(l) → H3O+(aq) + Cl-(aq)
 When something is donated, something else will
receive it. It's not obvious in the top reaction, but
it is water, H2O, that accepts the hydrogen. This
is how an acid can act as a proton donor - it gives
away it's hydrogen ion to a water molecule.
 View an animation of how HCl acts as an acid
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Let's take a closer look at how a base can
"accept a hydrogen ion". Our ammonia example
does a good job of showing this:
 NH3 (g) + H2O(l)
NH4+(aq) + OH–(aq)
 The ammonium ion, NH4+, was formed when
ammonia accepted a hydrogen ion. This makes
ammonia a base.
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The +1 charge results because the ammonium
ion has lost one electron.
 The H2O changes to OH– after giving up it's H+
 View an animation of how NH3 acts as a base
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Conjugate acid-base pairs differ from each
other by the presence or absence of a single
hydrogen ion (proton). Every acid has a
conjugate base, and every base has a
conjugate acid.
The conjugates will always be listed on the
product side of the reaction.
Substances that can act as an acid is one
reaction and as a base in another are called
amphoteric substances
 Example: In the first reaction the bisulfate ion,
HSO4– acts as a base. In the second reaction it
acts as an acid:
1. HSO4– + H3O+ ↔ H2SO4 + H2O
HSO4– accepts a proton from H3O+
2. HSO4– + OH– ↔ H2O + SO42HSO4– gives (donates) a proton to OH –
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Practice Problems 5.1.6
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Are acids that contain more than one
hydrogen ion that can be lost. Example:
Sulfuric acid, H2SO4 has two hydrogen ions
that it can give up. The first hydrogen ion is
released as:
H2SO4 (aq) → H+(aq) + HSO4-(aq)
The second hydrogen will be more difficult
to remove because it must now be removed
from a negative ion, HSO4-.
HSO4-(aq) → H+(aq) + SO42-(aq)
Acids that can donate more than one
hydrogen ion are called polyprotic
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How many H+ can citric acid, H3C6H5O7,
release?
What do you think the equations describing
the release of the H+ will be?
Citric acid can release three H+. The reactions
would be:
1. H3C6H5O7 (aq) → H+(aq) + H2C6H5O7-(aq)
2. H2C6H5O7-(aq) → H+(aq) + HC6H5O72-(aq)
3. HC6H5O72-(aq) → H+(aq) + C6H5O73-(aq)
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Assignment 5.1.7