8.3 Properties of Acids and Bases
One of the chemicals
used to make soaps is
sodium hydroxide.
Sodium hydroxide
reacts with animal or
vegetable fats to make
glycerol and soap.
Sodium hydroxide
belongs to a class of
compounds known as
bases.
8.3 Properties of Acids and Bases
Identifying Acids
What are some general properties of acids?
An acid is a compound that produces
hydronium ions (H3O+) when dissolved in water.
Some general properties of acids include
sour taste, reactivity with metals, and ability
to produce color changes in indicators.
8.3 Properties of Acids and Bases
Identifying Acids
When hydrogen chloride gas dissolves in water, it
ionizes and forms hydronium ions and chloride
ions.
HCl + H2O  H3O+ + Cl–
The solution that results is called hydrochloric
acid.
8.3 Properties of Acids and Bases
Identifying Acids
8.3 Properties of Acids and Bases
Identifying Acids
Sour Taste
Foods that taste sour often contain acids.
• Lemons, grapefruits, limes, and oranges
contain citric acid.
• Vinegar contains acetic acid.
• Dairy products that have spoiled contain butyric
acid.
8.3 Properties of Acids and Bases
Identifying Acids
Reactivity With Metals
The reaction between an acid and a metal is
an example of a single-replacement reaction.
When zinc is added to a test tube containing
hydrochloric acid, bubbles form in the tube.
Zn + 2HCl  H2 + ZnCl2
8.3 Properties of Acids and Bases
Identifying Acids
Color Changes in Indicators
An indicator is any substance that changes
color in the presence of an acid or base.
Litmus paper is made by coating strips of
paper with litmus, a kind of dye derived from
lichens.
Blue litmus paper turns red in the presence of
an acid.
8.3 Properties of Acids and Bases
Identifying Acids
Apples contain
several acids,
including malic
acid, ascorbic acid
(vitamin C), and
citric acid.
Blue litmus paper is
an indicator for
acids.
8.3 Properties of Acids and Bases
Identifying Bases
What are some general properties of bases?
A base is a compound that produces hydroxide
ions (OH–) when dissolved in water.
Some general properties of bases include
bitter taste, slippery feel, and ability to
produce color changes in indicators.
8.3 Properties of Acids and Bases
Identifying Bases
Sodium hydroxide, NaOH, is an example of a
base.
When sodium hydroxide dissolves in water, it
dissociates into sodium ions and hydroxide ions.
NaOH  Na+ + OH–
8.3 Properties of Acids and Bases
Identifying Bases
The plaster in this boy’s cast contains a base.
8.3 Properties of Acids and Bases
Identifying Bases
Bitter Taste
Without sugar, chocolate tastes bitter. Cacao
beans contain a base that gives
unsweetened chocolate its bitter taste.
Many liquid medicines contain bases. Fruit
flavorings are often added to mask the taste
of these basic solutions.
8.3 Properties of Acids and Bases
Identifying Bases
Slippery Feel
Bases feel slippery. Wet soap and many
cleaning products that contain bases are
slippery to the touch.
When wet, some rocks feel slippery because
the water dissolves compounds trapped in
the rocks, producing a basic solution.
8.3 Properties of Acids and Bases
Identifying Bases
Color Changes in Indicators
• Bases turn red litmus paper blue.
• Phenolphthalein is another acid-base
indicator.
• In a solution containing a base,
phenolphthalein is red.
• In a solution containing an acid,
phenolphthalein is colorless.
8.3 Properties of Acids and Bases
Identifying Bases
These hydrangea flowers
contain natural indicators.
The color of the flowers
depends on whether the
plant is growing in acidic or
basic soil.
When hydrangeas grow in
acidic soil, the flowers are
bluish-purple. When
hydrangeas grow in basic
soil, the flowers are pink.
8.3 Properties of Acids and Bases
Neutralization and Salts
What are the products of neutralization?
The reaction between an acid and a base is
called neutralization.
The neutralization reaction between an acid
and a base produces a salt and water.
8.3 Properties of Acids and Bases
Neutralization and Salts
The negative ions in an acid combine with the
positive ions in a base to produce an ionic
compound called a salt.
The hydronium ions from the acid combine with
the hydroxide ions from the base to produce
water.
8.3 Properties of Acids and Bases
Neutralization and Salts
When hydrochloric acid reacts with sodium
hydroxide, a neutralization reaction occurs.
If you let the water in the resulting solution
evaporate, sodium chloride would crystallize out
of solution.
8.3 Properties of Acids and Bases
Neutralization and Salts
Table salt is the most common example of a salt
compound.
• Baking soda, NaHCO3, is produced during the
neutralization reaction between sodium hydroxide
and carbonic acid, H2CO3.
• The ocean contains many dissolved salts, including
chlorides and sulfates of potassium, calcium,
magnesium, and sodium.
8.3 Properties of Acids and Bases
Neutralization and Salts
The common salts listed in the table can all be
made by reacting an acid with a base.
8.3 Properties of Acids and Bases
Proton Donors and Acceptors
What are proton donors and proton
acceptors?
Acids can be defined as proton donors, and
bases can be defined as proton acceptors.
8.3 Properties of Acids and Bases
Proton Donors and Acceptors
When an acid and a base react in water, a proton
from the hydronium ion from the acid combines
with the hydroxide ion (OH–) from the base to
form water (H2O).
Acids lose, or “donate,” protons. Bases “accept”
protons, forming water, a neutral molecule. This
definition allows you to classify a wider range of
substances as acids or bases.
8.3 Properties of Acids and Bases
Proton Donors and Acceptors
Based on the definitions of acids and bases that
you read earlier in this section, water is neither an
acid nor a base.
Using the proton-donor or proton-acceptor
definition, water can act as either an acid or a
base.
8.3 Properties of Acids and Bases
Proton Donors and Acceptors
When hydrogen chloride dissolves, water acts as
a base. It accepts a proton from hydrogen
chloride and becomes a hydronium ion.
8.3 Properties of Acids and Bases
Proton Donors and Acceptors
When hydrogen chloride dissolves, water acts as
a base. It accepts a proton from hydrogen
chloride and becomes a hydronium ion.
8.3 Properties of Acids and Bases
Proton Donors and Acceptors
When hydrogen chloride dissolves, water acts as
a base. It accepts a proton from hydrogen
chloride and becomes a hydronium ion.
8.3 Properties of Acids and Bases
Proton Donors and Acceptors
When ammonia dissolves, water acts as an acid.
It donates a proton to the ammonia, which acts as
a base.
8.3 Properties of Acids and Bases
Proton Donors and Acceptors
When ammonia dissolves, water acts as an acid.
It donates a proton to the ammonia, which acts as
a base.
8.3 Properties of Acids and Bases
Proton Donors and Acceptors
When ammonia dissolves, water acts as an acid.
It donates a proton to the ammonia, which acts as
a base.
8.3 Properties of Acids and Bases
Assessment Questions
1. What ion is formed when a base dissolves in
water?
a.
b.
c.
d.
hydroxide ion
hydronium ion
hydrogen ion
sodium ion
8.3 Properties of Acids and Bases
Assessment Questions
1. What ion is formed when a base dissolves in
water?
a.
b.
c.
d.
hydroxide ion
hydronium ion
hydrogen ion
sodium ion
ANS: A
8.3 Properties of Acids and Bases
Assessment Questions
2. What products are formed in a neutralization
reaction?
a.
b.
c.
d.
an acid and a base
water and a proton
a base and a salt
water and a salt
8.3 Properties of Acids and Bases
Assessment Questions
2. What products are formed in a neutralization
reaction?
a.
b.
c.
d.
an acid and a base
water and a proton
a base and a salt
water and a salt
ANS: D
8.3 Properties of Acids and Bases
Assessment Questions
3. In the reaction between ammonia and water to
form an ammonium ion, water acts as a(n)
a.
b.
c.
d.
acid because it donates an electron to ammonia.
base because it donates an electron to ammonia.
acid because it donates a proton to ammonia.
base because it donates a proton to ammonia.
8.3 Properties of Acids and Bases
Assessment Questions
3. In the reaction between ammonia and water to
form an ammonium ion, water acts as a(n)
a.
b.
c.
d.
acid because it donates an electron to ammonia.
base because it donates an electron to ammonia.
acid because it donates a proton to ammonia.
base because it donates a proton to ammonia.
ANS: C
8.3 Properties of Acids and Bases
Assessment Questions
1. A food that contains acidic compounds can often
be identified by its bitter taste.
True
False
8.3 Properties of Acids and Bases
Assessment Questions
1. A food that contains acidic compounds can often
be identified by its bitter taste.
True
False
ANS:
F, sour