Environmental Science

Grade Level: Intermediate
Magnetism

Using BTB Indicator

Investigation: Students will use Bromothymol blue solution to determine whether a

substance is an acid or a base.

Subject Integration: Human Body, Respiration, Carbon Cycle.

Teacher Preparation:

Materials: Water

Vinegar

Ammonia

Newspaper

Small plastic cups

Wax paper

Paper towels

Bromothymol blue

Science Information:

There are many indicators used in chemistry. An indicator changes color

when its pH changes. Most indicators have a range of about 2 levels. Using

the appropriate indicator for a particular substance will cause the indicator to

change color. The pH range of Bromothymol blue (BTB) is 6-8 so it can be used

to indicate an acid or a base. It will be yellow to yellow-green in an acid

solution and will be blue in a base solution.

Animals exhale Carbon dioxide gas. Carbon dioxide (CO₂) can be detected by

exhaling into the acid indicator solution, Bromothymol blue. The water in the

Bromothymol blue solution mixes with the CO₂ an produces Carbonic Acid.

Over time, the dissolved CO₂ gas willcome out of solution and return to the

atmosphere. Bromothymol blue will slowly return to its original blue color.

Resources:

Concise Science Dictionary (1991). Pub: Oxford University

Press, New York. ISBN 0-19-286102-6

Van Cleave, Janice (1993). A+ Projects in Chenmistry

Pub: Wyley & Sons. ISBN 0-471-58630-7

Introduction:

Discuss household cleaners, particularly ammonia and vinegar (i.e., ammonia
is used in glass cleaner, vinegar is used in coffee pots, etc.)
Safety: Discuss the dangers of common cleaners if used improperly.

Activity 1 Procedure:

Cover student work areas with newspaper. Distribute all supplies except straws.
Have students place 5 drops of vinegar on the wax paper.
With a clean, pipette, place BTB one drop at a time on the vinegar until there is an
apparent color change.
Thoroughly rinse out the pipette.
Repeat the test with ammonia.

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