“Chameleon flowers” experiment
How to make paper flowers that change their color
In spring the flowers blossom, including chemical ones! In this experiment we’ll see how they can change color depending on pH.
A similar experiment is included in the MEL Chemistry subscription.
- wear protective gloves, a mask and glasses;
- work in a well-ventilated room;
- observe safety rules when working with fire and heating devices.
Warning! Only under adults supervision.
Reagents and equipment:
- 1 ml of sodium pyrosulfite solution (2.5 mol/l);
- 2 ml of citric acid solution (1.5 mol/l);
- aqueous solution of thymol blue (0.01 mol/l);
- 3 pieces of white paper;
- wooden sticks;
- conical flask;
Make origami flowers and place them on sticks. Then paint the flowers with thymol blue. Pour solutions of sodium pyrosulfite and citric acid into the flask. Heat the mixture. Place the flowers in the flask and watch the color change from blue to red. Without heating the colors turn orange.
In the reaction of sodium pyrosulfate and citric acid, sulfurous gas is released, and the higher the temperature, the more intensively it is released:
Na₂S₂O₅ + H8C₆O₇ → Na₂H₆C₆O₇ + H₂O + 2SO₂
The released sulfurous gas dissolves in the water that contains the thymol blue indicator. Sulfurous acid is formed, which changes the potential of hydrogen (pH) of the solution. As a result the indicator changes color from blue to red.
SO₂ + Н₂О = Н₂SO₃
Without heating the gas is released more slowly and evaporates from the flowers more quickly than it reaches them. This makes the color less saturated, and the flowers turn orange.