Color change chemical experiments

Some of the most interesting examples of color change experiments of different substances are:

• The Briggs–Rauscher reaction
• Experiments with pH indicators
• The Olympic Rings Experiment
• The experiment to create milk, wine and beer
• The blue bottle experiment
• Old Nassau’s reaction
• Oxidation-reduction experiments
• The Vanishing Colors Experiment
• The Liquid Thermometer Experiment

The Briggs–Rauscher reaction

The Briggs-Rauscher reaction is one of the most impressive. It is an oscillating reaction, that is, it changes color after a few minutes, in a cyclical way. It is made with three colorless solutions and the color changes occur instantly. In this reaction, iodine is transformed into other elements. This experiment must be carried out in a laboratory, under certain safety conditions and due precaution.

• Materials:
  • Solution A requires 0.2 M potassium iodate (KIO ₃ ) and 0.08 M sulfuric acid (H ₂ SO ₄ ).
  • Solution B consists of 3.6 M hydrogen peroxide (H ₂ O ₂ ).
  • Solution C is composed of 0.15 M allonic acid (CH ₂ (COOH) ₂ ); 0.02 M manganese sulfate (MnSO ₄ ) and 3% w/v starch.
• Preparation: in an Erlenmeyer flask with a shaker, pour 50ml of each solution according to their ABC order. It is necessary to respect this order and dump them quickly. The solution will be clear at first, then amber, later dark blue, and then colorless again. This cycle can be repeated several times.

Experiments with pH indicators

Experiment with purple cabbage

With the different pH indicators it is possible to change the color of the water to make it look like wine or blood. This experiment can be easily carried out at home but taking the necessary precautions since some of the elements to be used are corrosive and toxic.

pH indicators are substances that are added to a solution of unknown pH to determine its degree of acidity or alkalinity. This is demonstrated when the substance in question changes color. This change allows you to visually determine the pH value or range of the solution.

Although pH solutions can be easily found in any laboratory, it is also possible to find them in the natural pigments of some vegetables. For example, pigments called anthocyanins, which are part of various plants, change color depending on pH, from red to blue, purple, and green.

• Materials:
  • red or purple cabbage
  • Lemon juice
  • Vinegar
  • Alcohol
  • Detergent
  • Baking soda
  • Ammonia
  • Bleach
  • Water
  • Salt
  • transparent glasses
  • Knife
  • spoons
• Preparation: cut the red cabbage and put it to boil. Pour the purple juice that is obtained in nine transparent glasses. In each one of them put a little of one of the nine mentioned ingredients: lemon juice, vinegar, alcohol, detergent, baking soda, ammonia, salt and water. Mix well with a spoon. Each glass will then turn red, blue, or green. The purple color of cabbage works as a neutral liquid for pH measurement. By adding each compound, the purple color will turn red, if it is an acid solution; in blue if it is neutral; and in green if it is a base or alkaline substance.

blue bottle experiment

With this demonstration, we will be able to transform a blue liquid into a transparent one and vice versa. This experiment must be carried out in a laboratory and taking care when handling the different elements.

• Materials:
  • 1 1 liter Erlenmeyer flask, with lid
  • 5g sodium hydroxide (NaOH)
  • 5g glucose
  • 0.1% methylene blue solution
  • Tap water
• Preparation: Fill the Erlenmeyer flask halfway with water. Dissolve in it the 5 g of sodium hydroxide and the 5 g of glucose. Then add 1ml of the methylene blue solution. Cover the container and shake it to mix all the materials. Observe how the solution turns blue. By letting it rest, it will become transparent again. When you shake it again, it will be blue again. This reaction can be repeated several times.

Christmas experiment

Like the previous experiments, this chemical demonstration is done with pH indicator solutions. As the colors that we will obtain will be red and green, this experiment can be special for Christmas parties. It is important to be careful with the materials and avoid inhalation or contact with the eyes or skin.

• Materials:
  • Distilled water
  • 15 grams of glucose
  • 7.5 grams of sodium hydroxide (NaOH)
  • Indigo Carmine pH Indicator
  • Beakers or other transparent containers
• Preparation: make solution A with 750ml of distilled water and 15 grams of glucose. For solution B, mix 250ml of distilled water with 7.5 grams of sodium hydroxide. Heat solution A until it reaches 36-37°C and add a small pinch of indigo carmine to it. The solution will turn blue. Then, pour solution B into solution A. In this way, the color will change from blue to green. After a while the color will be red and later yellow. To restore the green color, pour the solution into an empty beaker, from a height of about 60 centimeters. This will allow the solution to come into contact with oxygen and thus the color will be green again, then red, then yellow, repeating the cycle again.

Experiment for Valentine

Like the blue bottle experiment, other colors can be obtained depending on the pH indicator used. In this case, a beautiful pink color will be obtained, ideal for Valentine’s Day. When heated, the pink color will be intense and, when cooled, it will disappear.

• Materials:
  • phenolphthalein pH indicator
  • concentrated ammonia
  • Water
  • Glass container
• Preparation: mix a drop of concentrated ammonia in 500 milliliters of water. Add a few drops of phenolphthalein. Heat the mixture to obtain the pink color. Upon cooling, the mixture will again be colorless.

olympic rings experiment

With this experiment you can achieve the typical colors of the Olympic rings: blue, black, red, yellow and green.

• Materials:
  • 5 identical transparent glasses
  • 1 container
  • 5 grams of ferric ammonium sulfate (NH ₄ Fe(SO ₄ ) ₂ )
  • Water
  • Potassium thiocyanate (KSCN) for red color
  • Potassium ferrocyanide (K ₄ [Fe(CN) ₆ ]) for the blue color
  • Tannic acid (C ₇₆ H ₅₂ O ₄₆ ) for the black color
  • Tartaric acid (C ₄ H ₆ O ₆ ) for green color
  • Sodium bisulfite (NaHSO ₃ ) for the yellow color
• Preparation: place in a container 500 ml of water and 5 grams of ferric ammonium sulfate. Arrange the clear cups like the Olympic rings. In each of them, dissolve 1/2 gram of the mentioned elements to obtain each color. Add a little of the solution of water and ferric ammonium sulfate to each. Observe how the colors of the Olympic rings appear.

Experiment with milk, wine and beer

This experiment makes it possible to transform water into substances visually very similar to wine, milk and beer. It is important to wear gloves and protective glasses, in addition to taking safety precautions when handling the chemicals that will be used in the experiment, since they can cause burns and poisoning.

• Materials:
  • Distilled water
  • Saturated sodium bicarbonate with 20% sodium carbonate with pH 9
  • pH indicator phenolphthalein (C ₂₀ H ₁₄ O ₄ )
  • Saturated aqueous solution of barium chloride (BaCl ₂ (H ₂ O) ₂ )
  • Sodium dichromate crystals (Na ₂ Cr ₂ O ₇ )
  • Concentrated Hydrochloric Acid (HCl)
  • 2 transparent glasses
  • 1 cup
  • 1 mug of those used to drink beer
• Preparation: it is essential to prepare the glasses, the cup and the jug beforehand, since the experiment depends, to a large extent, on the products that are going to be added in them before pouring the “water”. Fill 3/4 of the glass of water with distilled water. Add 20-25 ml of saturated sodium bicarbonate to it. In the wine glass put a few drops of phenolphthalein. In the glass of milk, pour 10 ml of the barium chloride solution. In the beer mug, place a small amount of sodium dichromate crystals. Just before pouring out the contents of the glass of water, add 5 ml of hydrochloric acid to the beer mug. Finally, place the rest of the contents of the glass of water in the glass of wine, the glass of milk, and the mug of beer to turn the “water” into each of these drinks.

Old Nassau’s reaction

This experiment is ideal for surprising guests during Halloween. The chemical reaction that occurs changes the color of the solution from orange to black.

• Materials:
  • Water
  • soluble starch
  • Sodium disulfite (Na ₂ S ₂ O ₅ )
  • Mercury(II) chloride (HgCl ₂ )
  • Potassium iodate (KIO ₃ )
• Preparation: to carry out this experiment it is necessary to prepare 3 solutions, which we will call solution A, B and C. For solution A, mix 4 grams of starch in a little water. Stir the paste into 500 ml of boiling water and allow the mixture to cool to room temperature. Then add 13.7 grams of sodium disulfite. Add more water to obtain 1 liter of solution.
• To prepare solution B, dissolve 3 grams of mercury(II) chloride in water. Then, add more water to complete 1 liter of solution. For solution C, dissolve 15 grams of potassium iodate in water. Add more water to complete 1 liter of solution.
• Finally, mix 50 ml of solution A with 50 ml of solution B. Place this mixture in 50 ml of solution C.
• The color of the mixture will be orange after a few seconds. After a while, the mixture will turn a bluish-black color.

Oxidation-reduction experiment

This experiment is very useful to see how oxidation-reduction reactions occur and to obtain a pink solution.

• Materials:
  • 100 ml of a 0.133 M glucose solution (C ₆ H ₁₂ O ₆ )
  • 100 mL of a 1.0 M solution of sodium hydroxide (NaOH)
  • 1 ml of a 0.1% resazurin solution
  • 1 Erlenmeyer flask of 250 ml or 500 ml
  • Top
  • Pipette
• Preparation: For solution A, mix 2.4 g of glucose in distilled water to make 100 ml of solution. For solution B, dissolve 4 g of sodium hydroxide by pouring it little by little and stirring constantly into enough distilled water to make 100 ml. To prepare solution C, dissolve 0.1 g of resazurin in distilled water to form a 100 mL solution. This will result in a blue colored solution. Subsequently, pour solution A and solution B into the flask. To this mixture, add 8 drops of solution C. Stopper the flask and shake it to mix all the components, which at first will have a bluish color. Let the mixture rest. Within 10 minutes, the solution will be colorless. Shaking it again will turn it pink. This can be repeated several times, letting stand or shaking the solution. The effect will last one hour, after this time the color will fade.

vanishing colors experiment

This is another simple oxidation experiment where the colors will disappear as if by magic. It can be done at home with caution as bleach is corrosive and can cause poisoning.

• Materials:
  • Water
  • food dyes
  • Bleach
  • Dropper
  • glass or jar
• Preparation: fill a glass or jar halfway with water. Add a few drops of food coloring. Stir until the solution turns coloured. Then add a few drops of bleach until the color begins to disappear. Then add drops of another colorant. This time, the color will not spread as in pure water but will disappear. This happens because the bleach contains sodium hypochlorite that oxidizes with the color molecules of the food dyes and causes a reaction where they can no longer reflect light.

liquid thermometer experiment

In this experiment, colors will change from pink to blue based on temperature, just like a thermometer.

• Materials:
  • transparent container
  • 3 g cobalt(II) chloride hexahydrate (CoCl ₂ )
  • 500 ml of alcohol
• Preparation: mix the 3 g of cobalt chloride hexahydrate (II) and the alcohol in a container. Warm the solution just slightly above room temperature. Add water until the blue solution cools and turns pink. Alternatively, this pinkish solution will turn blue if heated, and turn pink again when cooled.

Other curious color change experiments

In addition to the experiments already mentioned, there are many more to try and observe the color changes. Some of them are:

• The transformation of water into liquid gold
• The rainbow experiment
• The experiment with flames

The transformation of water into liquid gold

With this experiment it is possible to turn water into a golden liquid and very similar to gold. For this, it is necessary to prepare two solutions.

• Materials:
  • 1 gram of sodium arsenite (Na ₃ AsO ₃ )
  • 5.5 ml glacial acetic acid
  • 10 grams of sodium thiosulfate
  • 100 ml of water
  • transparent containers
• Preparation: Mix sodium arsenite and glacial acetic acid in a container with water to obtain solution A. Prepare solution B by stirring sodium thiosulfate in another container with water. Pour one solution into the other. As a result, a clear solution will be obtained, which will turn golden after about 30 seconds.

rainbow experiment

This experiment is ideal for looking at all the colors on a pH scale.

• Materials:
  • A long glass tube with a cap
  • Universal indicator (solution)
  • 0.02 M hydrogen chloride (HCl)
  • 0.02 M sodium hydroxide (NaOH)
  • syringe or pipette
• Preparation: fill a long glass tube with the universal pH indicator. With the aid of a syringe or pipette, put a few drops of 0.02 M hydrogen chloride in the bottom of the tube and cap it well. Then add a couple of drops of 0.02M sodium hydroxide and recap. The universal indicator will react with the elements at the ends of the tube and display the full range of pH colors, forming a rainbow.

Another rainbow experiment

There is also a simpler variant of this experiment. To do it, you can use the liquid that remains after boiling red or purple cabbage.

• Materials:
  • transparent straw
  • lemon juice or vinegar
  • Baking soda or soap powder
• Preparation: fill the transparent straw with the red cabbage juice. Add a little lemon juice or vinegar to one end and seal it. Then add baking soda or soap powder to the other end and cap it. Observe how a rainbow of colors is formed.

flame experiment

In addition to the chemical experiments on color change in solutions, interesting experiments can be carried out with flames, taking all the necessary care. In this case, different elements can be identified, depending on the color that appears in the flame.

• Materials:
  • A piece of nickel chrome wire or a piece of wood or cotton swab
  • Hydrochloric or nitric acid
  • Distilled water
  • Lighter
  • ionic salt solution
  • samples to identify
• Preparation: If a piece of wire is to be used, immerse it in hydrochloric or nitric acid. Then rinse it with distilled water. If you get close to the flame and there is a small burst of color, it is not clean enough. Once fully cleaned, it should be immersed in an ionic or metallic salt solution or powder. Then place it in the flame and observe the color that appears. The wire must be cleaned after each test. If a piece of wood is used, soak it in distilled water overnight. Then, rinse it with tap water, using gloves or tweezers so that it does not get contaminated with sodium from the sweat of your hands. Subsequently, take the piece of wood or the cotton swab and dip it into the sample to be identified. Quickly pass it over the flame and pay attention to the color that emerges. It is important to note that this experiment is approximate and may be inaccurate for some elements or compounds.

Color guide:

• From carmine to magenta – these are lithium compounds.
• Scarlet red: they are strontium compounds.
• Yellow-red: it is a calcium compound.
• Golden yellow: indicates the presence of iron.
• Intense yellow: these are sodium compounds.
• Brilliant white: it is a magnesium compound.
• Greenish white: indicates the presence of zinc.
• Emerald green: they are usually copper compounds.
• Brilliant green: identifies boron.
• Intense blue: may indicate the presence of lead, selenium, bismuth, cesium, or copper.
• Light blue: these are arsenic compounds.
• Purple violet: they are potassium compounds.
• From lilac to purple-red – can indicate potassium, rubidium or cesium compounds.

Bibliography

• Lister, T. Classical Chemistry Experiments. (2002). Spain. Synthesis.
• Fernández Braña, M. An amusing chemistry. (2016). Spain. Editorial Tebar Flores.
• Petrucci, R. General Chemistry. (2017). Spain. pearson.