C5.7C DESCRIBE TESTS THAT CAN BE USED TO DISTINGUISH
AN ACID FROM A BASE
REVIEW
pH paper
indicators – liquid and paper
ACTIVITIES
Sponge Indicator (see page two)
Slippery bases (see page three)
Disappearing ink pg (see page four)
LABS
Household Acids & Bases (see page five)
Exploring Acids, Bases and Indicators (see page six and seven)
Make Your Own Acid-Base Indicator: Turmeric (see page eight)
Karyn Schoof and Paul Voydanoff
1
Indicator Sponge
Source: Flinn Chem Topic Labs
Acids & Bases Volume 13
p. 81
ISBN 1-877991-81-3
Summary: A sponge is soaked in congo red to act as an indicator sponge.
Use HCl with red food coloring added and NaOH with blue food coloring
added. As the sponge is out from one solution to another, it will change
from red to blue.
Karyn Schoof and Paul Voydanoff
2
Slippery Bases
Source: A Demo A Day
Borislaw Bilash II
p. 180
Flinn Scientific Inc
ISBN 1-877991-43-6
Summary: Using small slivers of Ivory Soap. Students can wet their
fingers, then rub it over the soap and feel that bases are slippery.
Students can take litmus paper in plain water and soapy water, to see the pH
change and to understand that soap is basic.
Karyn Schoof and Paul Voydanoff
3
Disappearing Ink
Source: A Demo A Day
Borislaw Bilash II
p. 183
Flinn Scientific Inc
ISBN 1-877991-43-6
Summary: Make a solution of ethyl alcohol with a few drops of
thymolphalein and enough NaOH that makes the solution a deep blue color.
Using a white cotton shirt, transfer the solution onto the shirt. In a few
minutes the “ink” spot will disappear.
Karyn Schoof and Paul Voydanoff
4
Household Acids and Bases
This lab is modified from a lab on page 458 of the Modern Chemistry text
by Holt, Rinehart and Winston
Summary:
The juice from boiled red cabbage can be used as an acid-base indicator.
Use common household items, such as mayonnaise, soft drinks, milk or
baking soda.
If any of your substances are solids, mix them with a small amount of water.
Add a few drops of the red cabbage solution to the solution you are testing
and note the color change.
Karyn Schoof and Paul Voydanoff
5
Acids and Bases
This lab is from the text Living by Chemistry
Published from Key Curriculum Press
The purpose of this lab is to use common household products with a cabbage
and a universal indicator to determine if the solution is an acid or a base.
Solution
Formula
Vinegar
C2H4O2
Rubbing
Alcohol
0.1 M Salt
Solution
C 3 H8 O
0.1M
Hydrochloric
Acid
Window
Cleaner
Drain Cleaner
HCl
Washing Soda
(Laundry
Detergent)
Antacid Tablets
Na2CO3
Lemon Juice
C6H8O7
Cabbage Juice
Color
Universal
Indicator
Color
Number on the
pH Scale
NaCl
NH4OH
0.1M NaOH
CaCO3
Karyn Schoof and Paul Voydanoff
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Identify each tested material as an acid or a base:
Solution
Acid
Base
Vinegar
Rubbing Alcohol
0.1 M Salt Solution
0.1M Hydrochloric Acid
Window Cleaner
Drain Cleaner
Washing Soda (Laundry
Detergent)
Antacid Tablets
Lemon Juice
Karyn Schoof and Paul Voydanoff
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Make Your Own Acid-Base Indicator
1. Place 1/2 teaspoon of turmeric (from your grocery spice section) in a
small sealable plastic bag, and add 5 mL of methyl hydrate. (You might use
gasoline antifreeze from the hardware store).
Caution! A parent should supervise this experiment, since methyl hydrate is
poisonous if consumed, and also flammable. If someone does drink the
methyl hydrate, make them throw up immediately, and get them to a
hospital.)
2. Let the mixture sit overnight.
3. Cut a coffee filter into strips about 1 cm by 5 cm, and thoroughly soak the
strips in the turmeric solution. The turmeric solution may stain your clothes
and skin yellow. You may wish to wear disposable plastic gloves when
working with the solution.
4. Dry the strips on a paper towel. The dry strips can be used as acid-base
indicator paper. Turmeric is yellow in acids and red-brown in bases.
5. Use the indicator paper to test household materials to see if they are
noticeably acidic or basic. Here are some examples of materials you might
test with the turmeric paper: vinegar, milk of magnesia, ammonia-based
window cleaner, lemon juice, apple cider, table salt, Ivory soap, any dish
detergent, and Vitamin C tablet (ascorbic acid), any soft drink, tomato juice,
milk, borax, washing soda, baking soda, dill pickles, and tap water.
Methyl hydrate dissolves a special type of colored dye from the turmeric.
The dye can exist in two forms: in acids, the dye is turned into its yellow
form, and in bases the dye is turned into its red-brown form.
Karyn Schoof and Paul Voydanoff
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