Details activity Length 30 mins. Topics chemical Reactions Activity form Discrepant event (Demonstration only) Language English publish

In this activity, students room fooled by an acid-base colour-changing reaction, and learn just how chemistry can define this wonder result.

You are watching: What color does phenolphthalein turn in an acid

Phenolphthalein is one indicator — a chemistry which transforms colour relying on whether that meets an acid or a base. It transforms purple if it meets other basic, such together ammonia; it stays colourless if the meets one acid like vinegar or a neutral substance prefer water.

In this magic trick, the phenolphthalein in beakers 1 and 3 will revolve purple once you mix it v the ammonia in beakers 2 and 4. When you to water the two purple solutions right into the large beaker, the acidic vinegar neutralizes the basic ammonia. The phenolphthalein becomes colourless.


Acid: Acids are compounds v excess H+ ions. The term comes from the Latin native acidus that means “sharp” or “sour”. Some basic properties that acids room that castle taste sour, react through metal, adjust the shade of litmus record from blue to red, and have a short pH (0 – 7). Examples of acids are vinegar and lemon juice.Base: A compound that has an overfill of OH- ions. An additional word because that base is alkali. Some simple properties that bases room that they have the right to be provided as family members cleaners, rotate red litmus file blue, and have a high pH (7 – 14). Some instances of bases are ammonia and baking soda.Indicator: A substance that indicates the level of acidity or alkalinity of a solution through characteristic shade changes.


describe the prestige of monitoring when doing science.

Explain the chemistry behind a an easy acid-base reaction.


Per Demo or Group:2 huge beakers4 little beakersPhenolphthaleinAmmoniaVinegarWater*all chemicals and also solutions room readily easily accessible from science supply stores.

Key Questions

Were every the beakers of “water” the very same to begin with? What is an acid? What is a base? What happens when an mountain is blended with a base? Why might an indicator like phenolphthalein be beneficial in chemistry?

What to Do

Preparation:Do the adhering to preparation the end of students’ view.

Hint: ammonia evaporates rather quickly, therefore cover the ammonia beakers if you preparing more than a couple of minutes prior to you do the trick.

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Label four tiny beakers 1 come 4.In 1 and also 3, put in 5 drops of phenolphthalein.In 2 and 4, placed in 5 autumn of ammonia.In one big beaker, put in 20 drops of vinegar.Fill the other big beaker through water (for pouring into little beakers).


Pour water into each beaker (1-4) so each is half full.Announce the you will now “magically” change the colour of the “water” by mixing two beakers that water together. Ask students to watch carefully and also describe the colour together you pour 1 into 2, and 4 into 3. Watch as they both turn purple-pink!“Shtick” in ~ the ready, ask college student in a mysterious voice to report what lock see as soon as you mix with each other the 2 coloured solutions.Dump both remedies together right into the large beaker (laced with vinegar) and watch together they come to be colourless again!


can you predict the colour phenolphthalein will turn when included to milk? How around orange juice? shot it out with some other typical solutions. try making your very own cabbage juice acid-base indicator.

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