DetailsActivity Length30 mins.TopicsChemical ReactionsActivity TypeDiscrepant event (Demonstration only)LanguageEnglishPrint

In this activity, students are fooled by an acid-base colour-changing reaction, & learn how chemistry can explain this magical result.

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Phenolphthalein is an indicator — a chemical which changes colour depending on whether it meets an acid or a base. It turns purple if it meets something basic, such as ammonia; it stays colourless if it meets an acid like vinegar or a neutral substance lượt thích water.

In this magic trick, the phenolphthalein in beakers 1 and 3 will turn purple when you phối it with the ammonia in beakers 2 và 4. When you pour the two purple solutions into the large beaker, the acidic vinegar neutralizes the basic ammonia. The phenolphthalein becomes colourless.

Vocabulary:

Acid: Acids are compounds with excess H+ ions. The term comes from the Latin word acidus that means “sharp” or “sour”. Some basic properties of acids are that they taste sour, react with metal, change the màu sắc of litmus paper from blue to red, & have a low pH (0 – 7). Examples of acids are vinegar and lemon juice.Base: A compound that has an excess of OH- ions. Another word for base is alkali. Some basic properties of bases are that they can be used as household cleaners, turn red litmus paper blue, và have a high pH (7 – 14). Some examples of bases are ammonia and baking soda.Indicator: A substance that indicates the degree of acidity or alkalinity of a solution through characteristic màu sắc changes.

Objectives

Explain the importance of observation when doing science.

Explain the chemistry behind a simple acid-base reaction.

Materials

Per kiểm tra or Group:2 large beakers4 small beakersPhenolphthaleinAmmoniaVinegarWater*all chemicals and solutions are readily available from science supply stores.

Key Questions

Were all the beakers of “water” the same to lớn begin with?What is an acid?What is a base?What happens when an acid is mixed with a base?Why might an indicator like phenolphthalein be useful in chemistry?

What to Do

Preparation:Do the following preparation out of students’ view.

Hint: ammonia evaporates quite quickly, so cover the ammonia beakers if you’re preparing more than a few minutes before you vày the trick.

Label four small beakers 1 to 4.In 1 and 3, put in 5 drops of phenolphthalein.In 2 & 4, put in 5 drops of ammonia.In one large beaker, put in đôi mươi drops of vinegar.Fill the other large beaker with water (for pouring into small beakers).
*

Instructions:

Pour water into each beaker (1-4) so each is half full.Announce that you will now “magically” change the colour of the “water” by mixing two beakers of water together. Ask students to lớn observe carefully & describe the colour as you pour 1 into 2, và 4 into 3. Watch as they both turn purple-pink!“Shtick” at the ready, ask students in a mysterious voice to lớn report what they see when you phối together the two coloured solutions.Dump both solutions together into the large beaker (laced with vinegar) and watch as they become colourless again!

Extensions

Can you predict the colour phenolphthalein will turn when added to lớn milk? How about orange juice? Try it out with some other common solutions.Try making your own cabbage juice acid-base indicator.

Other Resources

Science World | YouTube | Using Purple Cabbage to vì some Chemistry!


Artist: Jeff Kulak

Jeff is a senior graphic designer at Science World. His illustration work has been published in the Walrus, The National Post, Reader’s Digest and Chickadee Magazine. He loves to make music, ride bikes, và spend time in the forest.


Artist: Jeff Kulak

Jeff is a senior graphic designer at Science World. His illustration work has been published in the Walrus, The National Post, Reader’s Digest và Chickadee Magazine. He loves lớn make music, ride bikes, và spend time in the forest.


Artist: Jeff Kulak

Jeff is a senior graphic designer at Science World. His illustration work has been published in the Walrus, The National Post, Reader’s Digest & Chickadee Magazine. He loves to make music, ride bikes, & spend time in the forest.


Artist: Michelle Yong

Michelle is a designer with a focus on creating joyful digital experiences! She enjoys exploring the potential forms that an idea can express itself in và helping then take shape.


Artist: Michelle Yong

Michelle is a designer with a focus on creating joyful digital experiences! She enjoys exploring the potential forms that an idea can express itself in and helping then take shape.


Artist: Michelle Yong

Michelle is a designer with a focus on creating joyful digital experiences! She enjoys exploring the potential forms that an idea can express itself in và helping then take shape.


Artist: Ty Dale

From Canada, Ty was born in Vancouver, British Columbia in 1993. From his chaotic workspace he draws in several different illustrative styles with thick outlines, bold colours and quirky-child like drawings. Ty distils the world around him into its basic geometry, prompting us khổng lồ look at the mundane in a different way.


Artist: Ty Dale

From Canada, Ty was born in Vancouver, British Columbia in 1993. From his chaotic workspace he draws in several different illustrative styles with thick outlines, bold colours & quirky-child like drawings. Ty distils the world around him into its basic geometry, prompting us lớn look at the mundane in a different way.


Artist: Ty Dale

From Canada, Ty was born in Vancouver, British Columbia in 1993. From his chaotic workspace he draws in several different illustrative styles with thick outlines, bold colours and quirky-child like drawings. Ty distils the world around him into its basic geometry, prompting us to lớn look at the mundane in a different way.

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