Teachers TryScience

Magic breath

Oct 14 2016

Source: vascsc-tts-guj

Summary Information

Keywords:

Magic Breath, Lime water, Phenolphthalein, Carbon Dioxide, Carbonic acid, Calcium Carbonate, neutralization reaction, Acid, Base, Salt, Water, chemical rea

Topic:

Biology

Chemistry

Workplace Skills:

Raising Questions

Problem Solving

Investigation Design

Discussion

Recording & Reporting

Independent Thinking

Estimated Time Required:

less than 1 hour

Target Grade (Ages):

Grade 6 (Ages 11-12)

Grade 7 (Ages 12-13)

Grade 8 (Ages 13-14)

Diversity Indicators:

Teachers or students

Watch this Lesson in Practice

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LESSON

Goals and Prerequisites

Goals:

To understand effect of Phenolphthalein on acid and base.
To carry out Neutralization reaction.
To describe and illustrate the changes caused by the Neutralization reaction

Prerequisites:

Should be familiar with basic chemistry lab equipments
Should know about Acids, Bases, Salts and their indicators.

Instructional Objective(s)

Understand what a Neutralization reaction is
Know the science behind the so called magical breath
Know about phenolphthalein indicator and its effect on acids, bases and salts.

Instructional Resources

Background:

To understand this experiment better, one should be aware of a few concepts.

Acid: It is a substance which when added to water produces hydrogen ions [H⁺].

Base: A substance which when added to water produces hydroxide ions [OH^-].

Salt: An ionic compound made up of a cation (Positive ion) and an anion (Negative ion). It is one of the products of neutralization reaction.

This experiment is built on the fact that Phenolphthalein is colourless in Acid but gives pink colour with Bases.

You can have a short discussion on the above points with the students before starting the experiment.

Materials:

A transparent plastic glass
Straw
Lime Water (Ca(OH)2)
Phenolphthalein
Lab coat
Cleaning towels

Procedure:

Read through the entire experiment before starting
Take some lime water in a transparent plastic glass
Add 1-2 drops of Phenolphthalein indicator.
As lime water is a base, it gives Pink colour with phenolphthalein.
Take a straw and with the help of it blow into the glass containing Limewater.
Continue doing the same until you find some magic.
Observe the change in the colour of Lime water

A salt is a compound derived from the neutralization of an acid and a base.

Acid + Base (Neutralization reaction) Salt + Water

Procedure:

Addition of 1 to 2 drops of phenolphthalein to lime water (base) produces a pink colour. This base can be neutralized by exhaling CO2 into the solution, which forms carbonic acid (H2CO3) after reacting with water. This carbonic acid neutralizes the base and the solution turns from pink to colourless. This is because of the formation of a salt, calcium carbonate (CaCO3), and water (H2O).

The neutralization is indicated by a change of colour from pink to colourless.

CO₂ + H₂O -------> H₂CO₃

Carbon dioxide Water Carbonic Acid

Ca(OH) ₂ + H₂CO₃ ------> CaCO₃ + 2H₂O

Lime water Carbonic Acid Calcium Carbonate + Water .

Tips

Do not swallow the phenolphthalein containing limewater while breathing out in it.
Make sure the drops of the same do not go inside your eyes.
You can try the same experiment using different types of bases and indicators.

Credits

Image courtesy: Vikram A Sarabhai Community Science Centre

RESOURCES

Original Resources

How-to's

Magic Breath

Contributed Resources

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STANDARDS/CURRICULUM

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