Acids
and
Bases
A Short Introduction
Acids and Bases Are Everywhere
• Look around you and every liquid you
see will probably be either an acid or
a base.
• The only exception would be distilled
water. Distilled water is just water.
That's it.
• Most water you drink has ions in it. It
is those ions (H+ or OH-) which make
something acidic or basic.
Acids and Bases Are Everywhere
• In your body there are small
compounds called Amino Acids.
Those are acids.
• In fruits there is something called
Citric Acid. That’s an acid too.
• When you put baking soda in water
it makes a base.
• Vinegar is an acid. It is a weak
solution of Acetic Acid in water.
pH Scale
• Scientists use something called the
"pH" scale to measure how acidic or
basic a liquid is.
• The scale goes from “1" to "14".
Distilled water is 7 (right in the
middle).
pH Scale
Acids are found between “1" and “6".
Bases are from “8" to "14".
Most of the liquids you find every day have a
pH near "7", either a little below, or a little
above.
When you start looking at the pH of
chemicals the numbers go to the extremes.
If you ever go into a chemistry lab, you
could find solutions with a pH of "1" and
others with a pH of "14". Those chemicals
are very dangerous.
A Quick Comparison of Acids and Bases
The name acid comes
from the Latin word
acidus, which means
“sour”.
When dissolved in
water, acids have a
sour taste.
Acids cause the dye in
litmus paper to change
from blue to red.
Water solutions of base
feel slippery or soapy to
the touch.
When fatty substances
are placed in a base
solution, they dissolve.
Bases cause the dye in
litmus to change from
red to blue.
Household cleaning
products contain a base.
What
Really
Happens?
A Little Tricky, but Here Comes the Straight Answer.
Acid Vs. Base
Acids are compounds which break into
hydrogen (H+) ions and another
compound when placed in an
aqueous solution (water).
Bases are compounds which break up
into hydroxide (OH-) ions and
another compound when placed in
an aqueous solution (water).
One More Time…
• If you have an IONIC compound and you put it in
water it will break apart into two ions.
• If one of those ions is H+ … The solution is
acidic.
• If one of the ions is OH- … The solution is basic.
• There are other ions which make acidic and
basic solutions, but we won’t be talking about
them here.
pH Scale… One More Time
• The pH scale we talked about is actually a
measure of the number of H+ ions in a
solution.
• If there are a lot of H+ ions, the pH is very
low.
• If there are a lot of OH- ions, that means
the number of H+ ion is very low, so the pH
is high.
Vocabulary to Know
ACID = a solution that has an excess of H+
ions.
BASE = A solution that has an excess of OHions. Another word for base is ALKALI.
AQUEOUS = A solution which is mainly
water. Think of the word aquarium.
STRONG ACID = An acid which has a very
low pH (1-4).
STRONG BASE = A base which has a very
high pH (11-14).
More Vocabulary to Know
WEAK ACID = An acid that only partially
ionizes in an aqueous solution. That means
not every molecule breaks apart. They
usually have a pH close to 7 (5-6).
WEAK BASE = A base that only partially
ionizes in an aqueous solution. That means
not every molecule breaks apart. They
usually have a pH close to 7 (8-10).
NEUTRAL = A solution which has a pH of 7.
It is neither acidic or basic.
Examples of
Acids and Bases
Examples of Acids and Bases
H2SO4
HCl
(Sulfuric Acid)
(Hydrochloric Acid)
HC2H3O2
(Acetic Acid)
NaOH
(Sodium
Hydroxide)
KOH
(Potassium
Hydroxide)
HNO3
(Nitric Acid)
Acid-Base Indicators
• An acid-base indicator is a weak acid or
a weak base.
• Indicators are substances that change
color depending on whether the
solution is acid or alkaline.
• You need to know the names and colors
of some common indicators.
Acid-Base Indicators
• An indicator does not change color from
pure acid to pure alkaline (basic) at
specific hydrogen ion concentration, but
rather, color change occurs over a range
of hydrogen ion concentrations.
• This range is termed the color change
interval. It is expressed as a pH range.
Common Indicators
Litmus, red in acid solution, blue in
alkaline solution.
Phenolphthalein, colorless in acid
solution, pink in alkaline solution.
Universal indicator, has a range of
colors depending on the strength
of the acid or alkali.
pH Numbers of
‘Everyday’ Substances
Dilute hydrochloric acid, 1.5
Lemon juice, 2.5
Orange juice, 3.5
Pure water, 7.0
Blood, 7.5
Milk of magnesia, 10.5
Dilute sodium hydroxide, 13.0
It’s
Your
Turn!
Were You Sleeping on the Job?
Quick Quiz
A substance that exhibits a sour taste.
A substance that exhibits a bitter taste.
A substance that reacts with metals to
produce hydrogen gas.
A substance that feels slippery to the
touch because it dissolves the surface of
the skin.
Quick Quiz Continued
A substance that has a pH of
greater than 7.
A substance that has a pH of less
than 7.
A substance which turns blue
litmus paper red or cause no
change to red litmus paper.
A substance which turns red litmus
paper blue or cause no change to
blue litmus paper.
That’s basically it.
(Ha Ha, get it?)