Download Acids and Bases

Look at some examples, and
see if you can figure out
what an acid is…
HCl (Hydrochloric acid)
HNO3 (Nitric acid)
H2SO4 (Sulfuric acid)
H3PO4 (Phosphoric acid)
Official definition:
(or one of the definitions, anyway)
Acids are substances that give away hydrogen
ions.
Example: HCl gives away hydrogen to water:
HCl (aq) + H2O  H3O+ (aq) + Cl- (aq)
Draw the hydrogen ion. What does it consist of?
A hydrogen ion is simply a
proton.
Acids are also called “proton donors.”
Tell-tale signs of an acid:
 sour taste
(orange juice and lemonade contain
citric acid)
 turns litmus paper red
(by reacting with a chemical in
the litmus paper)
 reacts with metals to produce
hydrogen gas
Examples of acids:
• Vinegar
• Lemon Juice
• Soft Drink
• Battery Acid
• Stomach Acid
• Apple Juice
• Black Tea
Chemists write the formulas for acids
with the H at the front, so they’re easy to
identify as acids:
HCl (Hydrochloric acid)
HNO3 (Nitric acid)
H2SO4 (Sulfuric acid)
H3PO4 (Phosphoric acid)
An acid is a proton donor
A base is a proton acceptor
base
acid
Acids and Bases:
An acid is a compound that donates H+
ions:
HCl + H2O  H3O+ + Cl A base is a compound that accepts H+
ions. In the equation above, water is
acting as a base.
 btw: H3O+ is called the hydronium ion
Looking at the last
two reactions, notice
that water acted as an
acid in one, and as a
base in the other.
Substances that can act as an
acid or a base are called
amphoteric.
Tell-tale signs of a base:
 bitter taste
 slippery feel
 turns litmus paper blue
(Conveniently, base, bitter, and blue all
start with B!)
Examples of bases:
• Detergent
• Baking Soda
• Drain Cleaner
• Ammonia
• Soaps (hand, dish)
• Antacid
• Conjugate acids and bases:
H
Cl H
acid
+
O
H
base
+
H
HO
+
Cl
H
• Acids and bases are identified based on
whether they donate or accept H+.
• Remember, though, most reactions are
reversible. Look at the reverse reaction. Can
you identify an acid and base in the reverse
reaction?
• Conjugate acids and bases:
H
Cl H
acid
+
O
H
base
+
H
HO
+
Cl
H
conjugate acid conjugate base
conjugate acid-base pairs
• Acids and bases are identified based on
whether they donate or accept H+.
• “Conjugate” acids and bases are found on the
products side of the equation. A conjugate
base is the same as the starting acid minus H+.
Conjugate Acids and Bases:
 The Bronsted-Lowry definitions:
HCl + H2O  H3O+ + ClThe forward reaction is a reaction between
an acid (HCl) and a base. The reverse
reaction is also a reaction between an
acid (H3O+) and a base.
Acids and Bases:
HCl + H2O  H3O+ + ClAfter the acid HCl donates its proton, it becomes
a base (Cl-). A conjugate base is the
substance that results after an acid donates a
hydrogen ion to a base.
It’s a base, because it could take the H+ back
again. And what do we call something that can
take H+?
Acids and Bases:
HCl + H2O  H3O+ + ClAfter the water accepts the H+ ion from
HCl, it becomes H3O+, the conjugate
acid that can donate a proton.
Every acid-base interaction involves
conjugate acid-base pairs.
Think of it like playing catch, with the H+
ion as the baseball. When you have it,
you’re the acid, after you throw it, you’re
the conjugate base.
Who is the acid, and who is the base?
Acids and Bases:
Summary





Acid – H+ donor
base – H+ acceptor
acid-base reaction
acid + base  conjugate base + conjugate acid
conjugate acid – what base becomes after it
accepts H+
 conjugate base – what acid becomes after it
donates H+
Practice problems 1 and 2:
Identify the acid, base, conjugate acid,
conjugate base, and conjugate acid-base pairs:
HC2H3O2(aq) + H2O(l)  C2H3O2–(aq) + H3O+(aq)
acid
base
conjugate base conjugate acid
conjugate acid-base pairs
OH –(aq) + HCO3–(aq)  CO32–(aq) + H2O(l)
base
acid
conjugate base conjugate acid
conjugate acid-base pairs
Practice: Identify the
conjugate acid-base pairs
in these reactions:
3. NH4+ + OH-  NH3 + H2O
4. HSO4- + H2O  H3O+ + SO42-
(5) HF(aq) + SO32–(aq)  F–(aq) + HSO3–(aq)
acid
base
conjugate base conjugate acid
(6)
conjugate acid-base pairs
CO32–(aq) + HC2H3O2(aq)  C2H3O2–(aq) + HCO3–(aq)
base
acid
conjugate base conjugate acid
(7)
conjugate acid-base pairs
H3PO4(aq) + OCl –(aq)  H2PO4–(aq) + HOCl(aq)
acid
base
conjugate base conjugate acid
conjugate acid-base pairs
Neutralization reactions:
If you combine an acid with
a base…
Predict the products:
HCl
+
NaOH 
?
Hint: It’s a special kind of double replacement
reaction!
If you combine an acid with
a base…
HCl
+
NaOH 
H 2O
+ NaCl
This is called a neutralization reaction
because the acid and base neutralize
each other.
If you combine an acid with
a base…
HCl
+
NaOH 
H 2O
+ NaCl
The products of any neutralization reaction
are water and a salt.
Acid/Base reactions:
Produce water and a salt (and sometimes carbon dioxide).
Hint: concentrate on the water first. Remember, water has
the formula HOH.
Complete and balance the following:
HCl +
2 HCl +
KOH

Ca(OH)2
HOH + KCl

Require equal numbers
2HOH
+ CaCl2

1.
Ba(OH)2 + H3PO4
2.
HC2H3O2
+ NaOH
3.
H2SO4 +
KOH
4.
H2CO3 + NaOH



Everyday application:
The stomach secretes acids to help digest
foods. These acids, which include
hydrochloric acid, have a molarity of
about 0.1M.
Antacids, like Tums, Maalox, Mylanta and
Alka-seltzer are simple bases that
neutralize stomach acids.
Naming acids
Look at the names of these acids – can
you come up with the rule?
H2SO4: sulfuric acid
HNO3: nitric acid
H3PO4: phosphoric acid
Naming acids
Rule #1: If the acid comes from a
polyatomic ion that ends in “ate,” the acid
is named ____-ic.
H2SO4: sulfuric acid (from sulfate)
HNO3: nitric acid (from nitrate)
H3PO4: phosphoric acid (from phosphate)
Naming acids
Rule #1: If the acid comes from a
polyatomic ion that ends in “ate,” the acid
is named ____-ic.
Practice: What is –
HC2H3O2?
HClO3?
H2CO3?
Naming acids
Rule #2: If the acid does not have oxygen
in it, then name it…
hydro + second element + ic
Example:
HCl is hydrochloric acid.
What would HBr be? H2S?
Acids and Bases:
Strength

What makes an acid a strong acid?
It ionizes completely in water!

1.
2.
3.
4.
5.
6.
These are strong acids (in order of increasing
strength):
HNO3 (nitric acid)
HCl (hydrochloric acid)
HBr (hydrobromic acid)
HI (hydroiodic acid)
H2SO4 (sulfuric acid)
HClO4 (perchloric acid) (the strongest)
Strong acids:
 HCl + H2O  H3O+ + ClRemember, strong acids ionize completely in
water. The reaction goes all the way to the
right. A single arrow is used. There are
virtually no HCl molecules left intact.
Strong acids:
 HCl + H2O  H3O+ + ClRemember, strong acids ionize completely in
water. The reaction goes all the way to the
right. A single arrow is used. There are
virtually no HCl molecules left intact.
Strong acids:
 HCl + H2O  H3O+ + ClLooking at the equation above, with the
single arrow, is Cl- a strong base or a
weak base?
General rule: The
conjugate base of a strong
acid is a weak base.
Similarly, the conjugate
acid of a strong base is a
weak acid.
One more reminder:
“Weak” does not mean the same
thing as “diluted.”
HCl, for example is always a strong
acid. If you add 1000 liters of water
to it, it will be diluted, but still strong
because what little there is will be
completely dissociated.
Electrolytes:
Acids and bases are both examples of
electrolytes.
Electrolytes are compounds that form ions
when dissolved in water.
They’re called electrolytes because they
can conduct electricity through water.
More on electrolytes:
If two wires connected to a light bulb and to a power
source are placed in a beaker of water, the light
bulb will not glow. If an electrolyte, such as
sodium chloride, is dissolved in the water, the light
bulb will glow because the solution can now
conduct electricity. The amount of electric current
that can be carried by an electrolyte solution is
proportional to the number of ions dissolved.
Thus, the bulb will glow more brightly if the
amount of sodium chloride in the solution is
increased.
Practice Questions
Which of these could be
used to determine
whether a substance is a
base?
A
B
C
D
Thermometer
Litmus paper
Balance
Bunsen burner
An element common to all
acids is –
a.
b.
c.
d.
chlorine
hydrogen
oxygen
sodium