This area addresses pH among different characteristics of solutions. It will be interesting for
students to classify a variety of solutions into acids and bases by using the characteristics of
the solutions.
Students observe changes after placing indicators into a variety of solutions and classify
them as acidic and alkaline. Students learn how the characteristics of the solution change
when acidic and alkaline solutions are mixed. Students are to conceive and explain
examples of how acidic and alkaline solutions are used in everyday life.
The grade 5 English science unit, Acids and Bases, meets the
academic content standards set in the Korean curriculum,
which state students should:
a) Observe changes after placing indicators into a variety
of solutions and then classify the solutions as acids and
bases.
b) Recognize the characteristics of acid and base
solutions.
c) Be aware through color change of indicators that
acidity and alkalinity weaken when the two types of
solutions are mixed.
d) Be able to find examples in everyday life in which the
characteristics of a solution change when acidic and
alkaline solutions are mixed.
What’s my target?
Things I need:
Have you ever eaten fruit that was still unripe? How did it taste?
This is how an acid tastes. It is sour. This is an example of a natural
acid. More powerful acids can also be made artificially. They can
exist as a liquid, solid or gas. Acids are generally most useful as
solutions of water. All acids contain hydrogen.
Lemon juice
Water
Cup
Teaspoon
Baking soda
Sugar
Bases are the opposite of acids. They have a bitter taste. Bases are
very good as cleaning agents. Weaker bases feel soapy when you
touch them. All bases contain hydroxides. Many bases do not
dissolve in water. The bases that do dissolve create an alkaline
solution.
What do I need to do?
1.
Fill a quarter of the cup with
lemon juice. Add an equal
amount of water. Taste a little
bit of the liquid.
2.
Add a teaspoon of baking soda
into the cup with the lemon juice
and water. Taste a little bit of the
lemon soda.
What happened?
Lemon Juice
3.
Add sugar to the lemon soda
to make it sweeter.
Draw a picture to show what happened when
you added the lemon juice with the baking soda.
Lemon Juice +
Baking Soda
Taste
What did I learn?
1. What do most acids taste like? Give an example of an acid.
_____________________________________________________________
2. What do most bases taste like? Give an example of a base.
_____________________________________________________________
1
What’s my target?
Things I need:
Blue litmus paper
Do you remember what an acid and base taste like? They taste
different, but you should never taste any chemical as it is extremely Red litmus paper
6 unknown samples
dangerous. You could make yourself really sick or even die.
Well plate
If we can't taste them, what is an easy way to tell an acid and base
apart? We can use indicators. The most common indicator is litmus
paper. This paper turns red in acids, blue in bases, or purple in
neutral solutions. Neutral means that it is not an acid or base.
Red litmus paper turns
blue in alkaline solutions.
What do I need to do?
1.
The teacher will pour 6 samples
into your well plate.
What happened?
Sample
1
2
3
4
5
6
2.
Dip a different strip of the red
litmus paper into each sample for
about one second and then
remove. Note the color.
Red Litmus Paper Color
3.
Dip a different strip of the blue
litmus paper into each sample
for about one second and then
remove. Note the color.
Blue Litmus Paper Color
What did I learn?
1. Which samples were acids? Which samples were bases? Which were neutral?
_____________________________________________________________
_____________________________________________________________
2. What would happen if you put blue litmus paper in an acid?
_____________________________________________________________
2
What’s my target?
Things I need:
Some indicators, such as universal indicator, have a huge range of
colors when they are added to different solutions.
Universal indicator
Well plate
6 unknown samples
If a strong acid is added to the indicator, it will turn red. If a strong
base is added to the indicator, it will turn blue. Each color has been
given a number which helps us to tell if the solution is a strong acid,
weak acid, strong base or weak base.
Strong acids have a pH of 1-3. Weak acids have a pH of 4-6. Weak
bases have a pH of 8-10. Strong bases have a pH of 11-14.If the
color is green and has a pH number of 7, the solution is neutral.
What do I need to do?
1.
The teacher will pour 6 samples
into your well plate.
2.
Dip a different strip of the
indicator paper into each sample
for about one second and then
remove.
3.
Compare the color with the
color chart within 5 seconds.
What happened?
Sample
1
2
3
4
5
6
Universal Indicator Paper Color
pH (number)
What did I learn?
1. What Universal Indicator paper colors indicate a base?
_____________________________________________________________
2. What pH numbers show that a test sample is a strong acid?
_____________________________________________________________
3
What’s my target?
Things I need:
Red cabbage juice also has a huge range of colors when it is added
to different solutions.
Red cabbage juice
Well plate
6 known samples
6 pipettes
The purple color in red cabbage is due to pigments called
anthocyanins. They are able to change colors when they are put in
acids and bases. This is because both acids and bases slightly change
the molecular structure of the anthocyanins. These new structures
absorb and reflect light differently which changes the colors we see.
The red cabbage juice changes to red in acids and blue-green in
bases. It stays purple in neutral solutions.
Red cabbage juice acidbase indicator pH chart.
What do I need to do?
1.
Pour a little of the red cabbage
juice into 6 of the holes on the
well plate.
2.
Use a pipette to add the test
chemicals to a different hole on
the well plate containing the red
cabbage juice.
3.
Compare the color with the
chart above.
What happened?
Sample
Dilute Hydrochloric Acid
Sprite
Bottled Water
Baking Soda Solution
Laundry Detergent
Pipe cleaner
Red Cabbage Juice Color
pH (number)
What did I learn?
1. Which samples were acids?
_____________________________________________________________
2. Which samples were bases?
_____________________________________________________________
4
What’s my target?
Things I need:
Dentists have recently started to warn people about the dangers of
drinking acidic drinks. They have found that acidic drinks dissolve
the enamel covering of the tooth. Drinking acidic drinks over a long
period of time means that the enamel disappears and the tooth
starts to crumble at the edges. This is known as erosion.
6 different drinks
Universal Indicator
or
Red cabbage juice
Well plate
Pipettes
Poster paper
What drinks should you stop drinking so that this doesn't happen to
you? Dentists say that if the pH level of the drink is below 5.5, then
tooth erosion will occur. The safe pH level for drinks is 5.5 and
above.
An example of tooth erosion.
What do I need to do?
1.
Decide which indicator you will
use to determine the pH’s of the
drinks. Inform your teacher.
What happened?
Drink
2.
Depending on the indicator you
chose, refer to the previous
experiments to refresh your
memory on how to complete the
experiment.
3.
Indicator Color
Use the results from your chart
to create a poster that warns
people about the dangers of
drinking acidic drinks.
pH
What did I learn?
1. Which drinks had a pH lower than the safe pH of 5.5?
_____________________________________________________________
2. What happens to people who drink acidic drinks over a long period of time?
_____________________________________________________________
_____________________________________________________________
5
What’s my target?
Things I need:
Acid rain is made when smoke from factories and motor vehicles,
such as cars, mix with the water in the air. It is the sulfur dioxide
and nitrogen oxides in the smoke that helps to make the acid rain.
The pH of this rain is below 5. In some cases, the pH has been lower
than 2.4.
30mL vinegar
Teaspoon
Salt
Cup
Dull 10 yen coin
Many structures are made from metal. Most bridges and motor
vehicles are made from steel. Copper can be used to make roofs
and other building parts. Acid rain destroys these metals little by
little. This is known as corrosion.
A power plant sending
smoke into the air.
What do I need to do?
1.
Pour 30mL of vinegar into a cup
and add a teaspoon of salt.
2.
Add a dull 10 yen coin and swirl
the cup. Wait for 5 minutes and
look at the 10 yen coin.
3.
Put the 10 yen coin back in the
cup with vinegar and leave it in
there for a month or so.
What happened?
Draw pictures to show before and after shots of the 10 yen coin.
What did I learn?
1. How is acid rain made?
_____________________________________________________________
_____________________________________________________________
2. What damage does acid rain do to metal objects?
_____________________________________________________________
_____________________________________________________________
6
What’s my target?
Things I need:
Many statues are made from limestone which is largely made from
calcium carbonate. Acid rain reacts with the calcium carbonate to
dissolve the statues.
Pipette
Chalk
Petri dish
Vinegar
Glue
Acid rain + Calcium carbonate = Salt + Carbon dioxide + Water
Eggshells and chalk are other examples of calcium carbonate.
People should do their best to use renewable sources of energy,
such as solar and wind power. These forms of energy produce much
less pollution and can help reduce acid rain. Car companies are also
trying to make cars that produce less harmful gases.
A statue damaged
by acid rain.
What do I need to do?
1.
Make a statue with two pieces of
white chalk.
2.
Put the chalk statue into a petri
dish.
3.
Use a pipette to put slowly
drop vinegar onto the chalk
statue.
What happened?
Draw a picture to show what happened to the chalk.
What did I learn?
1. What happens when acid rain falls on limestone statues?
_____________________________________________________________
2. What can people do to reduce acid rain?
_____________________________________________________________
_____________________________________________________________
7
What’s my target?
Things I need:
Acids will react with bases to make salts and water. This reaction is
called neutralization.
Ziploc bag
Vinegar
Paper towel
Baking soda
Acid + Base = Salt + Water
Measuring cylinder
If you add just the right amount of acid to a base, you can make the ½ tablespoon
liquid neutral. This means it has a pH of 7.
Neutralization is not only limited to solutions, but also when an acid
reacts with a carbonate.
Acid + Base (carbonate) = Salt + Water + Carbon dioxide
What do I need to do?
1.
Fill a Ziploc back with 125mL of
vinegar.
What happened?
2.
Put 1½ tablespoons of baking
soda on a paper towel and wrap
it up.
3.
Put the wrapped up paper
towel into the Ziploc bag and
quickly seal it up. Give it a little
shake and put it on the
ground.
Draw a picture to show what happened when you added an acid and a base (carbonate).
What did I learn?
1. What happens if you add an acid and a base together?
_____________________________________________________________
_____________________________________________________________
2. What is the pH of a neutral solution?
_____________________________________________________________
8
What’s my target?
Things I need:
If you keep adding an acid to a base or a base to an acid, you will
get to point where the solution is not acidic or alkaline. The
substance will be neutral. This means the pH will be 7.
Baking soda
Scales
Beaker
½ teaspoon
Vinegar
Well plate
Universal indicator
When people eat too much food, sometimes their stomach makes
too much acid. This acid rises into their throat and gives a burning
sensation. This is called heartburn. Antacid tablets can be taken to
help neutralize the extra acid the stomach is making. Antacids are
bases.
Sodium bicarbonate (baking soda) is sometimes used as an antacid.
What do I need to do?
1.
Dissolve 5g of baking soda in
200mL of water.
What happened?
Amount of antacid solution
added to the vinegar.
0mL
2.5mL
5.0mL
7.5mL
10.0mL
2.
Add ½ teaspoon of vinegar to 5
of the holes in the well plate.
The acid in your stomach is very dilute
hydrochloric acid. In this experiment, you
will use vinegar instead.
Universal Indicator Paper Color
3.
Add the amount of baking
soda solution as stated in the
chart below. Use pH paper to
determine the pH of the final
solution.
pH
What did I learn?
1. What causes heartburn?
_____________________________________________________________
_____________________________________________________________
2. How does taking antacids help?
_____________________________________________________________
_____________________________________________________________
9
What’s my target?
Things I need:
Alkaline solutions are used as cleaning products. The soap you use
to wash your hands with is a base. The washing detergent for
dishes and the laundry detergent for cleaning clothes are all bases.
Even baking soda can be used to clean stains.
Coffee
Large bowl
White cloth
4 clothespins
Teaspoon
Water
Dishwashing liquid
Laundry detergent
Bleach
Soaps, detergents and stain removers clean up messes and help to
remove stains. They all do so in slightly different ways. Soaps are
made of particles that have two ends. One end sticks to the water,
while the other end sticks to the dirt. Detergents contain
surfactants, which are substances that reduce the surface tension
and helps dirt to mix with the water.
What do I need to do?
1.
Use a dry cloth that has been
stained with coffee and peg it
above a bowl full of water using
clothespins
What happened?
2.
Divide the cloth into 4 parts. Pour
5mL of water into the center of
part 1, 5mL of dishwashing liquid
in part 2, 5mL of laundry
detergent in part 3 and 5mL of
bleach in part 4.
3.
Wait 5 minutes. Then, wash
each part of the cloth in a bowl
of water.
Draw a picture to show what each part of the cloth looked like after you completed
step 3.
What did I learn?
1. What are many bases good at doing?
_____________________________________________________________
_____________________________________________________________
2. Which of the above cleaners removed the stain best?
_____________________________________________________________
10