Acids
Would you ever consider drinking a nice, cold glass of acid? Well, you most likely have sometime in your
life, and maybe even this morning!
Many common beverages such as lemonade, orange juice, or even soda contain substances called acids.
Acids are any compounds that increase the number of hydronium ions (H3O+) in solution when dissolved
in water. Hydronium ions are formed when an H+ breaks off from a compound and joins with a water
molecule. The resulting particle has a charge of 1+. Other acids are hydrochloric acid, nitric acid, sulfuric
acid, carbonic acid, acetic acid, ascorbic acid, or phosphoric acid. Acids can be found in many places from
factories to household kitchens. If you check out the ingredients in your lunch, you may find some acids.
Properties of Acids
Have you ever taken a bite of a lemon or a lime? If so, you have discovered one
property of acids – a sour taste. There is an acid in lemons, limes, and other
citrus fruits known as citric acid. However, tasting an unknown substance is
never a good idea as many acids are also corrosive – meaning they are capable
of “eating through” or dissolving other materials. Many acids are also
poisonous.
Indicators
So if you can’t taste a substance to check for acidity, how can you test for it? One way is by using an
indicator. An indicator is a substance that changes color when in the presence of acids or bases. For
instance, bromthymol blue is normally a pale blue color when in water. When an acid is added, it can turn
bright yellow! Litmus is another type of indicator. When blue litmus paper is exposed to an acid, it turns
red. Some indicators will have 2 reactions possible – 1 for acids and 1 for bases, but some can only test for
the presence of one type of solution.
Reactions and acids
Acids react with some metals to form hydrogen gas (H2). Think about what happened when
hydrochloric acid (HCl) was mixed with zinc metal – zinc replaced the less active hydrogen and
then the free H’s bonded to form bubbles of hydrogen gas. This reaction will occur as long as
the metal is an active metal (higher than H on an activity series). Acids will also react with
carbonates to produce carbon dioxide gas.
Acids and electricity
When acids are dissolved in water, they break apart into positive and negative ions in solution. The ions
make it possible for the solution to conduct an electric current. Car batteries (filled with sulfuric acid) are
an example of how this property can be used.
Other uses of acids
Sulfuric acid, which is the most widely made chemical in the world, can be used in the production of
paper, paint, and fertilizers. Nitric acid can be used in fertilizers, rubber and plastics. Hydrochloric acid
can be used to separate metals from their ores, keep pools algae-free, or help dissolve the food in your
stomach! Citric and ascorbic acids are found in orange juice. Carbonic and phosphoric acid help give that
sharp taste to many sodas, like Pepsi.
Bases
As opposed to acids, bases are compounds that increase the number of hydroxide ions, OH-, when
dissolved in water. Oxygen normally has a charge of -2 and the hydrogen has a charge of +1. Together,
they have a net charge of -1. For example, sodium hydroxide breaks down into positive sodium and
neagtive hydroxide ions.
NaOH  Na+ + OHHave you ever accidentally gotten soap or shampoo in your mouth in the shower? If so, you have
accidentally (and unfortunately) discovered a common property of bases. Bases are often described as
having a very bitter taste. Soaps and shampoos often show another characteristic of bases, the fact that
they are often slippery. However just like acids, tasting or feeling an unknown substance is never a good
idea as many bases are also corrosive and/or poisonous.
Bases and indicators
Bases can also be identified using indicators. Bromthymol blue, which is normally a pale blue color when
in water, will turn dark blue in the presence of a base. When a base is added to red litmus paper, the
paper turns blue. (A good way to remember is bases turn litmus blue.)
Bases and electricity
Solutions of bases can also conduct an electric current because they have the negative hydroxide ion
(OH-). This negative ion allows electrons to move through solution easily, carrying an electric current.
Uses of Bases
Sodium hydroxide can be used to make soap or paper, clean ovens, or unclog
drains. Calcium hydroxide (Ca(OH)2) is used to make cement or plaster.
Ammonia is found in household cleaners like Windex. Other bases such as
Mg(OH)2 or Al(OH)3 can be used as antacids to treat heartburn in milk of
magnesia. Bases can be found all around you!
Questions
1. Describe some similarities and differences between acids and bases.
2. What is an indicator? Give an example.
3. Most bases have the hydroxide ion (OH-) as part of the formula. Ammonia (NH3) is considered a
base, but does not have a hydroxide ion. How does ammonia qualify as a base? Think about the
definition of a base and what would happen when ammonia comes in contact with water.
4. If acids give off H+ ions and bases give off OH- ions, what do you think would occur if an acid is
mixed with a base?
5. Would you expect one solution to have turned blue litmus red and red litmus blue in your lab?
Why or why not?
Homework Assignment: Wanted poster
An acid is missing from the science supply closet! Design a wanted poster describing the properties of the
missing acid – at least 4. Include descriptions of tests a person could safely perform to determine if a
bottle found actually contains acid. Add any cautions of what a person should or should not do if they
encounter what they believe could be the missing acid. This poster should be colorful and creative!
Minimum size is 8.5” x 11”