Kool Demo for Acid-Base Reactions
Kool Demo for Acid-Base Reactions
Adapted from : http://www.stevespanglerscience.com/lab/experiments/color-changing-milk-of-magnesia
Materials:
Red cabbage juice indicator
(Distilled) water squirt bottle
2 large (500 ml) Erlenmeyer flasks or graduated cylinders
1, 100 ml graduated cylinder
1 large watchglass
Magnetic stir plate
2 magnetic stir bars
1 ringstand with large clamp
Milk of Magnesia
White vinegar
dry ice
Baking soda
Sharpie marker
Lab coat
gloves
Procedure
1. Pour 50ml indicator into both of the Erlenmeyer flasks. Label one ‘acid’ and the
other ‘base’.
2. Gently place a stir bar into each flask with the solution.
3. Place the ‘base’ flask on the stir plate/ringstand set-up and turn on the STIR so
that the solution is gently stirring (for set-up, see photo above).
4. Pour 50ml Milk of Magnesia into the 100 ml graduated cylinder. Dilute to 100ml
with distilled water.
Kool Demo for Acid-Base Reactions
5. Slowly pour this solution into the Erlenmeyer flask with the indicator. A green
color should appear quickly.
6. You can match this color to the ‘Reference Chart for Cabbage Juice Indicator’
and show students that it is indeed a basic household product.
7. Take this solution off of the stir plate and replace with the ‘acid’ Erlenmeyer flask.
8. Measure 50ml white vinegar to the 100 ml graduated cylinder then pour into the
second Erlenmeyer with the indicator solution. Alternatively you can simply drop
a small chunk of dry ice into the second Erlenmeyer flask. In this case, quickly
cover with the watchglass. In either case, the solution should quickly turn red.
9. You can match this color to the ‘Reference Chart for Cabbage Juice Indicator’
and show students that it is indeed an acidic household product.
Now for the Grand Finale:
10. Pour the basic solution from the first Erlenmeyer into the acidic solution from the
second Erlenmeyer. The solution should revert to its original purplish-red color
(cabbage indicator color).
11. You can match this color to the ‘Reference Chart for Cabbage Juice Indicator’
and show students that this was indeed an acid-base reaction and now the base
(Milk of Magnesia) neutralized the acid (white vinegar).
12. If you have indeed achieved true neutrality, you can now wash the solution down
the drain with PLENTY OF WATER TO DILUTE IT.
13. If it is not yet dilute, you can use baking soda (base) or white vinegar (acid) to
add to your experiment until the original purplish-red color is achieved.
Kool Demo for Acid-Base Reactions
Demonstration for Acid-Base Indicator Color Change
Basic Substance +
Indicator
Acidic Substance +
Indicator
Make Your Own Acid-Base Indicator…and Then Test It!
Make Your Own Acid-Base Indicator…and Then Test It!
http://www.stevespanglerscience.com/lab/experiments/red-cabbage-chemistry
Materials:
Red cabbage
(Distilled) water
Blender
Coffee filters
Rubber bands
2, plastic cups (per group)
1 Spot plate (per group)
Household products to test (ie. Baking soda, vinegar, ammonia, antacids, citrus juice)
1 disposable pipette (per group)
1 set of markers (per group)
Filter paper
Lab coats
gloves
Procedure: teacher
1. Peel off six big cabbage leaves and put them in a blender with 12 cups of
water. Liquefy! (This can be scaled-down or scaled-up as long as the
ration remains 1 leaf:2 cups water)
*note: test your water beforehand….if it is not close to pH 7.0 (±0.5 pH
units) then you should probably try to use distilled water.
2. Pour some of the mixture into one cup for each student group.
Make Your Own Acid-Base Indicator…and Then Test It!
Procedure: students
pH is the measure of how acidic or basic a substance is. A pH indicator is a chemical
that changes color based on how acidic or basic a substance is. When the indicator
comes in contact with a substance, the indicator's color corresponds to that substance's
approximate pH, which is a scale of zero to fourteen (with zero being the most acidic,
seven being neutral, and fourteen being the most basic) that indicates the acidity or
basicity of a substance. Red cabbage contains a pH indicator. You will make a solution
of pH indicator and test the pH of various household products.
3. Place a coffee filter loosely over a second cup and secure with a rubber band.
Carefully pour the cabbage mixture onto the filter. You should see only a deep
reddish-purple liquid in the second cup with no cabbage pieces.
4. Cabbage leaves can now be discarded in trash or compost bin! Save the liquid
as this is your indicator.
5. Obtain a 6 well plate. Choose six different commercial products and have
your teacher put a little in each well. Write down the name of which product is
in which well below. Get a variety of those from the ‘acid’ group and those from
the ‘base’ group.
Product"
1"
2"
3"
pH"
Acid"or"Base?"
1"
2"
3"
4"
4"
5"
6"
5"
6"
6. One at a time, pipette indicator one drop at a time until you see a color change.
GENTLY swirl the plate to mix everything.
7. Write down the color of each well after adding the indicator. Use the ‘Acid-Base
Color Chart for Cabbage Juice Indicator’ to estimate the pH of each product and
determine which are acids and which are bases.
Make Your Own Acid-Base Indicator…and Then Test It!
To make your own pH paper for easy testing on the go!
1--After you have made and strained the indicator so that only the purple liquid remains
(step 3), cut filter paper into thin (3*6 cm strips) and soak it in the juice until it obtains a
purplish hue when wet (depends on paper type but I soaked mine overnite for best
results).
2—Remove from the juice and hang it to drip dry on a washline with clothespins.
3—When dry you can spot different samples onto it with a disposable pipette or dip the
tip of the paper into a solution that you want to test. The Carbon Dioxide Acid Breath Test
The Carbon Dioxide Acid Breath Test
adapted from: NASA, EG-1998-03-118-HQ, The Brain in Space A Teacher’s Guide With Activities for
Neuroscience, Raising the Level of Carbon Dioxide in Your Blood and
http://www.stevespanglerscience.com/blog/experiment-of-the-week/do-you-have-acid-breath/
Pipe2e)
Stopper)
S"r)bar)
Flask)
S"rplate)
S"r)knob)
X"
Materials:
Phenolphthalein or universal indicator (see pH scale/color for each indicator)
Slightly basic tapwater (pH ~8)
KOH (finely ground)
Dry ice
2 Erlenmeyer flasks (per group)
1 Magnetic stir plate (per group)
2 magnetic stir bars (per group)
1, 2-hole rubber stopper (per group)
1, no-hole rubber stopper (per group)
1 disposable pipette (per group)
1 Normal drinking straw (per group)
Sharpie marker
Gloves for instructor
1 balloon (per group)
The Carbon Dioxide Acid Breath Test
Procedure: teacher
1. Set-up each Erlenmeyer/stir plate combination as depicted above.
2. Fill each Erlenmeyer with about 20 ml of tap water (not distilled water) and
drop in a stir bar. Add several drops of phenolphthalein or universal
indicator to one Erlenmeyer until a slight pink color (for phenolphthalein)
or green (for Universal indicator) can be seen. Quickly put on the
stopper/disposable pipette combination as depicted in the picture above.
Label that flask ‘indicator only’.
3. In the second Erlenmeyer, place 0.5 g of finely ground KOH, then several
drops of the indicator until a slight pink color (for phenolphthalein) or
green (for Universal indicator) can be detected. Quickly put on the stopper
as depicted in the picture above. Label that flask ‘indicator and absorber’.
Place this next to the stir plate set-up for later use.
Carbon dioxide (CO2) is a colorless gas. It’s responsible for giving soda its fizz and
plants use it for photosynthesis. We use oxygen to burn fuel for energy and CO2 is a
product of that process that we breathe out. CO2 levels in the air are very low,
however, in a closed environment such as a space shuttle, the amount of CO2 may
reach toxic levels. The level of CO2 must be closely monitored and removed from
the shuttle so that it does not poison the astronauts. In this activity, you’ll learn how
CO2 can affect pH (how acidic or basic a substance is) and how to counteract this
using a CO2 absorber.
Procedure: students
4. Place the “Indicator Only” flask on the stirplate and turn on the STIR (NOT
HEAT) so that the stir bar is slowly but steadily stirring your mixture. Move the
flask until the stir bar does not interfere with the pipette tip.
What is the color of the liquid in the flask? ___________________________
Answer: pink if using phenolphthalein or green if using universal indicator
5. Take your balloon and blow it up but DO NOT TIE IT. Hold it tightly so the air
does not escape.
6. Take your straw and place it over the tip of the pipette which is inserted into the
stopper of your flask.
The Carbon Dioxide Acid Breath Test
slowly
7. Place the end of your balloon over the straw and
loosen your grip so
that you can let the air enter into the straw. You can take turns with your own
balloon. The reaction is complete when you observe a color change. Once you
do you can stop. This color change alerts you that the solution has changed
from slightly basic to acidic.
What is the color of the liquid in the flask now? _____________________________
Answer: clear if using phenolphthalein or yellow to orange to red if using universal
indicator
8. Now switch flasks. Turn off the stirplate. Carefully remove this flask ‘indicator
only’ from the stir plate and replace it with the ‘indicator and absorber flask’.
What is the color of the liquid in the flask? ___________________________
Answer: pink if using phenolphthalein or green if using universal indicator
9. Slowly turn-on the STIR so that the solution is stirring slowly.
10. Remove the rubber stopper and USING TONGS drop a small piece of dry ice
into this second flask then quickly replace the rubber stopper.
11. Watch the liquid in the flask. Do you see a color change?
What is the color of the liquid in the flask? ___________________________
Answer: pink if using phenolphthalein or green if using universal indicator
The Carbon Dioxide Acid Breath Test
The chemical that is responsible for the color in the flasks is called [phenolphthalein or
universal indicator]. Use the chart showing the color of [phenolphthalein or universal
indicator] at different pH values to fill in the pH range of each of the flasks before and
after addition of CO2.
Indicator*only*
CO2#from#your#breath#
pH#range=________#
Indicator**
+*absorber*
pH#range=________#
Dry#ice#
pH#range=________#
pH#range=________#