Section 2.5—Characteristics
of Acids and Bases
Now that we know what acids are, how do they act?
Characteristics of Acids & Bases
Acids
Bases
Produce H3O+1 (hydronium
ion) in water
Produce OH-1 (hydroxide ion)
in water
Tastes sour
Tastes Bitter
React with active metals to
form hydrogen gas
Feels slippery
Strength versus Concentration
Review of how acids produce ions
water
acid
Hydrogen cation with some anion
Review of how acids produce ions
+1
-
Review of how acids produce ions
+1
Hydronium ion
Anion
Strong versus Weak Acids
-
-
How many hydronium ion – anion
pairs can you find?
3
+
-
How many intact acid molecules can
you find?
1
Strong acid
Most of the acid molecules
have donated the H+1 to water
Strong versus Weak Acids
How many hydronium ion – anion
pairs can you find?
+
1
How many intact acid molecules can
you find?
3
-
Weak acid
Only a few of the acid
molecules have donated the
H+1 to water
Concentrated versus Dilute
solute
Lower
concentration
Not as many solute (what’s
being dissolved) particles
solvent
Higher
concentration
More solute (what’s being
dissolved) particles
Combinations of Concentration & Strength
Concentrated
Dilute
Strong
A lot of acid
added & most
dissociates
Not much acid
added, but most of
what’s there
dissociates
Weak
A lot of acid
added, but most
stays together
Not much acid
added and most of
what is there stays
together
Other notes
All of the same ideas apply to bases as
well (concentration and strength)
Many people think all acids are dangerous
and all bases are more safe
Vinegar is an acid we eat…some of them are
safe!
Sodium hydroxide is a very caustic base…not all
of them are less harmful than acids!
The stronger and acid or base is (and the more
concentrated it is), the more dangerous it is for
you
pH
pH Scale
Is a scale to measure the acidity of a
sample
1
7
Highly acidic
neutral
14
Very basic
(not acidic)
Chapter 6 will give more detail about how pH is calculated!
Ways to measure pH
 Indicators change color based on pH
Liquid indicators – various indicators change colors at
different pH’s
Universal indicator – a combination of liquid indicators to
produce a “rainbow” changing colors at several pH’s
 Paper Indicators
Paper with a liquid indicator on it (Litmus paper or pH
paper)
 pH meters or pH probes
Electronically determine pH and give a read-out
Common pH indicators
This picture © 1998 David Dice
pH of common substances
SUBSTANCE
PH
Intestinal contents
6.5
0.1M HCl
1
Milk
6.5
Stomach contents
2
Urine
6.6
Vinegar
2.9
Bile
6.9
Soda pop
3
Saliva
7
Grapes
4
Blood
7.4
Beer
4.5
Eggs
7.8
Pumpkin pulp
5
0.1M NH3 (aq)
11.1
Bread
5.5
0.1M NaOH
13