Tag Archives: chemistry demonstration

Color Change Violets Chemistry Demonstration

The color change violets project works because violets are natural pH indicators.  (Robert & Pat Rogers)

The color change violets project works because violets are natural pH indicators. (Robert & Pat Rogers)

You can change violets from violet to green by exposing them to a household chemical. This is a fun chemistry demonstration, especially for the home.

Color Change Violet Materials

  • violets
  • household ammonia

Change the Color!

Really, nothing could be easier. Hold violets over ammonia and watch them change from blue or violet to green. You can speed the reaction if you use warmed ammonia or you can dip the flowers in the ammonia. The demo used to be performed as a sort of ‘trick’ using ammonia gas, which produces a quick and dramatic color change. With ordinary household ammonia, you can expect the color change to take a couple of minutes.

How It Works

Flowers, including violets, get their color from anthocyanins. This is a class of pigment molecules that changes color in response to pH. Ammonia is very basic, so it changes the blue color of violets to green. Violets come in other colors besides… well… violet, so expect a color change for these flowers too. The final color might not be green. For example, I tried this project using orange pansies (a form of violet) and got sort of a dull greenish-yellow color as a final result. Also, you can experiment with other flowers to get a color change in response to ammonia.

Learn More

Odor of Violets Chem Demo
Make a pH Rainbow Tube

Mercury Beating Heart Chemistry Demonstration

Mercury is a heavy silvery metal that is liquid at room temperature. In the Mercury Beating Heart experiment, a drop of mercury pulsates rhythmically, like a beating heart. Femto/Elementbox04

Mercury is a heavy silvery metal that is liquid at room temperature. In the Mercury Beating Heart experiment, a drop of mercury pulsates rhythmically, like a beating heart. Femto/Elementbox04

The mercury beating heart is a popular chemistry demonstration based on an an electrochemical redox reaction that causes a blob of mercury to oscillate, resembling a beating heart. Here’s how the Mercury Beating Heart works and how you can perform this chemistry demonstration yourself.

Mercury Beating Heart Overview

A drop of mercury is placed in a watch glass. The mercury is covered with a solution of an oxidizing compound in sulfuric acid. The oxidizer usually is potassium dichromate, hydrogen peroxide or potassium permanganate. An iron nail or wire is placed such that the tip of the nail is almost touching the mercury. The mercury will begin to pulsate rhythmically, like a beating heart.

Perform the Mercury Beating Heart Demo

  1. Place a drop of mercury in a watch glass, petri dish or saucer. 
  2. Pour sulfuric acid over the drop to cover it. The exact concentration of sulfuric acid is not critical. Car battery acid works for this demo. 
  3. Add a small amount of oxidizer, such as potassium permanganate, hydrogen peroxide or potassium dichlorate. Aqueous solution or a few crystals are fine. 
  4. When you are ready to start the beating heart, approach the drop of mercury with the tip of the iron wire or nail. The heart will start to beat when the iron is close to the mercury, but not quite touching it. The mercury heart will beat for about 20 seconds before stopping.

How the Mercury Beating Heart Works

The mechanism for this reaction is not clearly understood, but it may involve oxidation of the iron. The permanganate, peroxide or dichromate oxidizes the mercury to produce mercury(I) ions which combine with sulfate ions from the sulfuric acid to form a thin layer of mercury(I) sulfate on the surface of the drop of mercury. The formation of the layer reduces the surface tension of the drop, causing it to flatten out. When the flattened drops contacts the iron wire or nail, the mercury sulfate oxidizes the iron to form the iron(II) ion while reducing the mercury to its normal metallic form. The mercury has a higher surface tension, so the drop becomes rounded again. As contact with the iron ceases, the oxide coating starts to form again, repeating the process. When all of the oxidizer has been reduced, the reaction stops. There is some debate about the mechanism because weaker oscillations have been observed even without the presence of oxidizer.

Less Toxic Alternative to Mercury

Mercury is very toxic, so you may wish to perform this demonstration with another material. It turns out molten gallium may be substituted for the drop of mercury. Gallium will melt at a low temperature and is much less toxic/easily contained than mercury. To perform the demonstration with gallium, melt a pellet of gallium and immerse it in sulfuric acid. Add a small amount of an oxidizer, such as potassium permanganate, to the sulfuric acid. The gallium heart will be more slowly than the mercury heart.

Watch the Mercury Beating Heart in Action

It’s much safer to watch a video of this demonstration than to do it yourself. Here’s what happens…

 

Hot and Cold Color Change Chemistry Demonstration

Valentine’s Day Color Change Chem Demo

Watch a solution change from pink to clear and back again with the hot and cold demonstration. (Ty Nigh)

Watch a solution change from pink to clear and back again with the hot and cold demonstration. (Ty Nigh)

This is a fun color change chemistry demonstration, just right for Valentine’s Day. Take a pink solution and watch it turn colorless upon heating. When the solution cools it becomes pink again. Here’s what you do:

Prepare the Hot and Cold Valentine Solution

Add a few drops of phenolphthalein indicator and a drop of concentrated ammonia to 500 ml of water in a beaker, flask or large test tube.

Perform the Valentine’s Day Demo

Present the pink solution. You can heat the liquid over a hot plate or, in the case of the test tube, in a burner flame. Heating the solution causes a shift in the equilibrium between the unionized ammonia and the ionized ammonium hydroxide. The change in pH makes the pink-colored indicator turn colorless. If you do not experience a color change, there is too much ammonia in the solution, so dilute it further with water and try again.

More Valentine’s Day Science Experiments

The hot and cold demonstration is one of several Valentine’s Day science experiments to try:

Vanishing Valentine Chemistry Demonstration

Pink Color Change Chem Demo

If you have a separatory funnel available, try performing the Vanishing Valentine demo in that glassware, since it resembles a heart.  (Nick Ward)

If you have a separatory funnel available, try performing the Vanishing Valentine demo in that glassware, since it resembles a heart.  (Nick Ward)

Here’s a fun chemistry demonstration that’s perfect for Valentine’s Day or to illustrate an oxidation-reduction reaction. The Vanishing Valentine involves shaking a solution, causing it to turn pink. If the pink Valentine solution is left undisturbed, it will become colorless. The color change cycle can be repeated several times. It is caused by the oxidation and reduction of resazurin. an indicator that is pink or colorless depending on its oxidation state.

Vanishing Valentine Materials

  • 100 ml of a 0.133 M dextrose solution (C6H12O6)
  • 100 ml of a 1.0 M sodium hydroxide solution (NaOH)
  • 1 ml of a 0.1% resazurin solution
  • a 250-ml or 500 ml Erlenmeyer flask or separatory funnel (resembles a heart)
  • stopper for the flask
  • dropper or pipette

Prepare the Solutions

Dextrose Solution: Dissolve 2.4 g of dextrose in distilled or deionized water to make 100 ml of solution.

Sodium Hydroxide Solution: Prepare the 1.0 M sodium hydroxide solution by dissolving 4.0 g of sodium hydroxide in enough distilled or deionized water to make 100 ml of solution. Add the sodium hydroxide a little at time, stirring constantly. Heat is evolved from this reaction.

Resazurin Solution: Dissolve 0.1 g of resazurin in distilled or deionized water to make 100 ml of solution. The shelf life of resazurin solution is 6-12 months. This solution should be a deep blue color.

Perform the Vanishing Valentine Demonstration

  1. Pour 100 ml of dextrose solution and 100 ml of sodium hydroxide solution into the Erlenmeyer flask or separatory funnel. 
  2. Add 8 drops of resazurin indicator solution to the flask or funnel. 
  3. Stopper the solution and swirl the flask to mix the contents. Initially the solution will be blue
  4. Allow the solution to sit undisturbed. Once the resazurin is fully reduced the solution will become clear or colorless. This may take up to 10 minutes. 
  5. Swirl or shake the solution to turn it a pink Valentine color. 
  6. The clear-pink cycle may be repeated by allowing the solution to sit and then shaking it again. Once prepared, the solution lasts approximately an hour (depending on temperature and available oxygen in the flask). The pink color will become less vivid over time.

Vanishing Valentine Chemical Reactions

Dextrose irreversibly reduces resazurin to resorufin. The red resorufin molecule is further reduced (reversibly) to colorless dihydroresorufin. Dihydroresorufin (clear) may be oxidized back to resorufin (pink) by swirling or shaking the flask to introduce oxygen from the air into the solution.

Vanishing Valentine Demo Safety

Wear appropriate chemistry lab safety gear when performing this demonstration, such as a lab apron, gloves and safety goggles. While the resazurin and dextrose solutions are not hazardous, sodium hydroxide solutions are caustic and could produce a chemical burn if spilled on the skin or splashed into the eyes.
See the Vanishing Valentine in action:

Dancing Charcoal Chemistry Demonstration

The dancing charcoal chemistry demonstration is extremely exothermic, so your test tube might break. Use caution!. Neil Tackaberry, Flickr

The dancing charcoal chemistry demonstration is extremely exothermic, so your test tube might break. Use caution!. Neil Tackaberry, Flickr

Oxidation of Charcoal by Potassium Nitrate

Drop a small piece of charcoal into a test tube of melted potassium nitrate and watch the charcoal dance as it burns. This is a fun and simple chemistry demonstration that illustrates decomposition and oxidation (combustion) chemical reactions. It’s a nice introduction to exothermic chemical reactions, too.

Perform the Dancing Charcoal Chemistry Demonstration

Melt potassium nitrate (KNO3) in a test tube. Flaming the test tube with a gas burner works well. Decomposition of the potassium nitrate releases oxygen (O2).

2 KNO3 → 2 KNO2 + O2

Take a piece of charcoal that is small enough to fit inside the test tube. Flame it with the burner to heat it and drop it into the test tube. Rapid combustion of the charcoal will occur as the carbon in the charcoal reacts with the oxygen liberated by the potassium nitrate.

C + O2 → CO2

The piece of charcoal will bounce around inside the test tube or ‘dance’ as it is oxidized. Because a potassium salt is used as the oxidizer, the flame that is produced has a characteristic violet color.

If you like this demonstration, a similar fiery reaction occurs when you combine potassium chlorate and sugar to make “instant fire”.

Rainbow Wand Chemistry Demonstration

A rainbow wand works by varying the pH of a solution from one end of a tube to the other. A pH indicator provides the color

A rainbow wand works by varying the pH of a solution from one end of a tube to the other. A pH indicator provides the color change. (Derek Gavey)

An acid-base rainbow wand is an easy and colorful chemistry demonstration which illustrates the range of colors available for a pH indicator solution. Take a long glass tube and fill it with Universal Indicator solution. Add a few drops of 0.02M HCl to one end of the tube and seal it with a stopper. Add a couple of drops of 0.02M NaOH to the other end of the tube and seal it. The Universal Indicator will respond to the pH gradient by providing you with a lovely rainbow.

You can invert the tube a few times to speed things up.

Easy Rainbow Wand Home Chemistry Project

You can get a similar result using home chemistry. Fill a clear straw with red cabbage juice. Add a little lemon juice or vinegar to one end of the straw (acidic ingredient). Add a few drops of baking soda or laundry detergent solution to the other end of the straw (basic ingredient).

Simple Variation for a Rainbow Test Tube

A variation on the project is to mix in a pH indicator with gelatin or agar. After the gel sets, apply chemicals with different pH values to opposite sides of the mixture (you can use a pipette or syringe to deliver solution to the bottom of a test tube). Another way to set up the demonstration is to use sodium polyacrylate gel beads (water beads). Either the gel or the beads will slow the progression of the pH change, so you don’t need to use a super-long tube to get a nice rainbow effect.

Olympic Rings Chemistry Demonstration

Olympic Rings Chemistry Demonstration

Olympic Rings Chemistry Demonstration

Produce the colors of the Olympic rings in this easy chemistry color change demonstration. The colors of the Olympic Rings represent the colors of the flags of all the countries that participated in the 1912 Olympic Games. The Olympic Rings are blue, black, red, yellow, and green on a white background.

You can perform a chemistry demonstration in which you fill empty glasses, arranged like the Olympic Rings, with “water”. Once the clear liquid is added to the glasses, the colors of the Olympic Rings will appear.

Olympic Ring Materials

You need a container of 5 grams ferric ammonium sulfate in 500 milliliters of water. In separate glasses, dissolve about half a gram of the following solids in a few milliliters of water:

  • red – potassium thiocyanate
  • white – barium chloride
  • blue – potassium ferrocyanide
  • black – tannic acid
  • green – tartaric acid
  • yellow (amber) – sodium hydrogen sulfite

Perform the Olympic Rings Chem Demo

Olympic Rings

Olympic Rings

Arrange the glasses to form the order of the Olympic Rings. Try to use as small a volume as possible to dissolve the solids so the glasses will appear empty. Pour the ferric ammonium sulfate into the glasses and watch the colors develop!

  • red – thiocyanate ion forms a deep red complex with iron(III)
  • white – barium ion reacts with the sulfate ion to form a cloudy white precipitate
  • blue – ferrocyanide ion with iron(III) produces a deep blue compound
  • black – tannic acid with iron(III) forms a black complex
  • green – tartaric acid with iron(III) forms a greenish complex
  • yellow (amber) – hydrogen sulfite ion with iron(III) produces an amber compound

 Patriotic Colors Chemistry Demonstration

You can prepare a patriotic color demonstration for your country’s flag. For example, in the US, you’d use the chemicals to make red, white and blue. If you live in Brazil, prepare the chemicals to make green, yellow and blue.