barking dog experiment

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Barking Dog Reaction and Demonstration

The barking dog reaction is a classic chemistry demonstration that raises interest in science and illustrates combustion, an exothermic reaction , and physical chemistry concepts. The demonstrator ignites a mixture of carbon disulfide and nitrogen oxide, causing a bright blue chemiluminescent flash and a characteristic barking sound. The target audience is a high school or first year college chemistry class, although the reaction also entertains a general audience. Here is how to do the barking dog reaction and a look at its chemistry.

Barking Dog Reaction Materials

The reaction requires carbon disulfide, a nitrogen oxide, and a long cylindrical glass tube:

• Stoppered tube filled with either nitrous oxide (N 2 O) or nitric oxide (NO)
• Carbon disulfide (CS 2 )

Performing the Barking Dog Reaction

• Set the tube in a fume hood.
• Uncap the glass tube and add a few drops of carbon disulfide.
• Stopper the container and swirl the contents to mix them.
• Dim the lights.
• Light the lighter, uncap the tube, and ignite the vapor. Either use a long handled lighter or else use long tongs and drop a lit match into the tube.
• You can reignite the vapor a few times and repeat the demonstration.

Once lit, the flame front moves down the tube. As it does, the reaction produces a bright blue flash and woofing or barking sound. The diameter and length of the tube determines the sound of the bark. Yellow sulfur coats the inside of the tube as the reaction proceeds.

How the Barking Dog Reaction Works

Igniting the mixture of carbon disulfide with nitrous or nitric oxide initiates a combustion reaction . The products of the reaction are elemental sulfur, carbon dioxide, and nitrogen gas:

8 N 2 O + 4 CS 2  → S 8  + 4 CO 2  + 8 N 2 (for nitrous oxide) 8 NO + 4 CS 2  → S 8  + 4 CO 2  + 4 N 2 (for nitric oxide)

However, other reactions also occur, producing carbon monoxide (CO) and sulfur dioxide (SO 2 ).

The reaction proceeds as a wave traveling down the tube. In a long tube, it’s easy to follow the reaction progress. Slowing a video of the reaction in a short tube also shows the effect. The wave front compresses gas ahead of it, eventually causing it to explode. The harmonics of the sound of the explosion cause the barking sound. The gas compression also explains why you can re-light the mixture multiple times.

The blue light comes from chemiluminescence. Usually, you see chemiluminescence in liquids, as in a glow stick . The barking dog reaction is one of only a few reactions that displays gas phase chemiluminescence.

German scientist Justus von Liebig gets credit for revolutionizing chemistry education. He incorporated the chemistry lab as we recognize it today into the educational setting. The popularity of his barking dog reaction led him to perform the demonstration for the Bavarian royal family in April of 1853. Unfortunately, Liebig’s glass container shattered and sprayed shards of glass over himself and the royal family. No one was seriously injured, but Queen Therese received a minor cut on her cheek.

One explanation for Liebig’s mishap in his reaction between carbon disulfide and nitric oxide is that the nitrogen monoxide might have been contaminated with oxygen. Over time nitric oxide reacts with oxygen in air, forming nitrogen dioxide. Nitrogen dioxide is a powerful oxidizing agent .

Safety Information

Don’t repeat Liebig’s mistake! Perform the demonstration a safe distance from the audience, just in case something goes awry. The sound and light from the reaction are easily observable, so this isn’t a problem.

The barking dog reaction is a chemistry demonstration for the experienced chemistry teacher or lab technician. As with any chemistry demonstration, wear safety goggles and a lab coat. Carbon disulfide is flammable and toxic, so perform this demonstration within a fume hood. In any case, the end result is sulfur, which has an offensive odor.

• Brock, William H. (1997). Justus Von Liebig: The Chemical Gatekeeper . Cambridge, England: Cambridge University Press. ISBN 9780521524735.
• Jensen, William B. (2018). “Justus von Liebig – Chemistry Mentor and Teacher”. Preceptors in Chemistry . 6: 111-147. doi: 10.1021/bk-2018-1273.ch006
• Seabourne, Ché Royce; Maxwell, George; Wallace, James (2006). “Taming the Barking Dog”. Journal of Chemical Education . 83 (5): 751. doi: 10.1021/ed083p751

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Exothermic Reaction Examples - Demonstrations to Try

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 An  exothermic reaction  is a chemical reaction that releases heat and has a negative enthalpy (-ΔH) and positive entropy (+ΔS).. These reactions are energetically favorable and often occur spontaneously, but sometimes you need a little extra energy to get them started.

Exothermic reactions make interesting and exciting chemistry demonstrations because the release of energy often includes sparks, flame, smoke, or sounds, in addition to heat. The reactions range from safe and gentle to dramatic and explosive.

Steel Wool and Vinegar Exothermic Reaction

JMacPherson / Getty Images

The rusting of iron or steel is an oxidation reaction -- really just a slower form of combustion . While waiting around for rust to form wouldn't make for an interesting chemistry demonstration, there are ways to speed up the process. For example. you can react steel wool with vinegar in a safe exothermic reaction that evolves heat.

Barking Dog Exothermic Reaction

 Thomas Northcut / Getty Images

The "barking dog" reaction is a favorite exothermic chemistry demonstration because it emits a loud 'woof' or 'bark', similar to that of a dog. You need a long glass tube, nitrous oxide or nitric oxide, and carbon disulfide for this reaction.

If you don't have these chemicals, there is an alternative reaction you can do using a bottle and rubbing alcohol. It's not quite as loud or energetic, but it does produce a nice flame and an audible 'woofing' sound.

• How to do the Classic Barking Dog Reaction
• Alternative Barking Dog Reaction

Safe Laundry Detergent Exothermic Reaction

Glow Images, Inc.,/ Getty Images

Probably the simplest and easiest exothermic reaction is one you can try right at home. Simply dissolve powdered laundry detergent in your hand with a small amount of water. Feel the heat?

About the Laundry Detergent Exothermic Reaction

Elephant Toothpaste Exothermic Reaction

Jasper White / Getty Images

No list of exothermic reactions would be complete without the popular elephant toothpaste reaction. The heat of this chemical reaction is accompanied by a fountain of foam.

The classic form of the demonstration uses a hydrogen peroxide solution, potassium iodide, and detergent. There is also a kid-friendly version of the reaction that uses yeast and household peroxide and is safe enough for young hands to touch.

• Try the Elephant Toothpaste Reaction
• Try the Kid-Friendly Elephant Toothpaste Project

Sulfuric Acid and Sugar Exothermic Reaction

Uwe Hermann / Getty Images

Reacting sulfuric acid with ordinary table sugar (sucrose) results in an energetic exothermic reaction. Dehydrating the sugar pushes out a steaming column of carbon black, plus it makes the entire room smell like burnt marshmallows.

How to do the Sulfuric Acid and Sugar Reaction

Thermite Exothermic Reaction

Andy Crawford & Tim Ridley / Getty Images

The thermite reaction is much like rusting steel wool with vinegar, except the oxidation of metal occurs much more vigorously. Try the thermite reaction is you want burning metal and a lot of heat.

If you believe "go big or go home," then try performing the thermite reaction inside a block of dry ice. This amplifies the process and may even produce an explosion.

• Steps to perform the  Thermite Reaction (Safely)
• How to make Etch a Sketch Thermite

Sodium or Other Alkali Metal in Water

Dorling Kindersley / Getty Images

If burning metals is your cup of tea, you can't go wrong with simply dropping any alkali metal in water (unless you add too much). Lithium, sodium, potassium, rubidium, and cesium all react in water. As you move down the group in the periodic table, the energy of the reaction increases.

Lithium and sodium are fairly safe to work with. Use caution if you try the project with potassium. It's probably best to leave the exothermic reaction of rubidium or cesium in water to people who want to get famous on YouTube. If that's you, send us a link and we'll show off your risky behavior.

try the Sodium in Water Reaction (Safely)

Starting Fires Without Matches

 Lumina Imaging, Getty Images

Some exothermic chemical reactions spontaneously burst into flame without needing the help of a lit match. There are several ways to make a chemical fire -- all terrific demonstrations of exothermic processes.

How to make Chemical Fire Without Matches

Making Hot Ice Is an Exothermic Reaction

 Epop, public domain

Hot ice is what you get when you solidify sodium acetate from a supercooled solution. The resulting crystals resemble water ice, except they are hot instead of cold. It's a fun example of an exothermic reaction. It's also one of the common reactions used to make chemical hand warmers .

While you can buy sodium acetate, it's also extremely easy to make this chemical yourself by mixing baking soda and vinegar and boiling off the excess liquid.

How to make Hot Ice

More Exothermic Reactions To Try

Roz Woodward, Getty Images 

Many chemical reactions release heat, so these popular exothermic reactions are not your only options. Here are some other cool demonstrations to try:

• How to make Vesuvius Fire
• How to make a Baking Soda and Vinegar Volcano (yes, it's exothermic)
• Magic Genie in a Bottle Chemistry Demonstration
• Instant Fire Demonstration
• How to make Dancing Gummi Bears
• How to make Dancing Charcoal
• How to make Test Tube Thunderstorm
• Exergonic vs Endergonic Reactions and Processes
• What Is Fire Made Of?
• Examples of Chemical Energy
• Examples of Endothermic Reactions
• The Laws of Thermochemistry
• Why Is Fire Hot? How Hot Is Fire?
• Nuclear Fission Versus Nuclear Fusion
• The Chemistry Behind Sparklers
• The Discarded Phlogiston Theory in Early Chemistry History
• Colored Smoke Recipes
• Nuclear Fission Definition and Examples
• Electrochemical Cells
• Electrochemistry Calculations Using the Nernst Equation
• Standard Molar Entropy Definition in Chemistry
• The Science Behind Firecrackers and Sparklers
• Corium and Radioactivity After the Chernobyl Nuclear Meltdown

8 N 2 O + 4 CS 2   → S 8   + 4 CO 2   + 8 N 2 The "Barking Dog" is an exothermic chemical reaction ignited by a mixture of carbon disulfide and nitrous oxide. This combustion process, occurring in a cylindrical tube, results in a bright flash and a distinctive "woof" sound, reminiscent of a barking dog. Simply put, it involves the reaction of carbon disulfide (CS 2 ), a fuel, with nitrous oxide (N 2 O), an oxidizing agent, leading to the production of heat and elemental sulfur. The flame front in this reaction is a zone of highly luminous and hot gas, formed by the decomposition of the reactants.

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