experiments with sulphuric acid

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Sulfuric Acid and Sugar Demonstration

Easy & Spectacular Chemistry Demonstration

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One of the most spectacular chemistry demonstrations is also one of the simplest. It's the dehydration of sugar (sucrose) with sulfuric acid. Basically, all you do to perform this demonstration is put ordinary table sugar in a glass beaker and stir in some concentrated sulfuric acid (you can dampen the sugar with a small volume of water before adding the sulfuric acid ). The sulfuric acid removes water from the sugar in a highly exothermic reaction , releasing heat, steam, and sulfur oxide fumes. Aside from the sulfurous odor, the reaction smells a lot like caramel. The white sugar turns into a black carbonized tube that pushes itself out of the beaker.

Key Takeaways: Sulfuric Acid and Sugar Chemistry Demonstration

• Dehydrating sugar by reacting it with sulfuric acid makes for an entertaining and educational chemistry demonstration.
• The reaction produces a growing "snake" of black carbon, a lot of steam, and the odor of burning caramel.
• The demonstration illustrates an exothermic reaction and a dehydration reaction.

Chemistry Demonstration

Sugar is a carbohydrate, so when you remove the water from the molecule, you're basically left with elemental carbon . The dehydration reaction is a type of elimination reaction.

C 12 H 22 O 11 (sugar) + H 2 SO 4 (sulfuric acid) → 12 C ( carbon ) + 11 H 2 O (water) + mixture water and acid

But wait... sugar does not contain water, does it? How can it get dehydrated? If you look at the chemical formula for sugar, you'll see a lot of hydrogen and oxygen atoms. Combining two hydrogen atoms with one oxygen atom makes water. Removing the water leaves behind the carbon. Although the sugar is dehydrated, the water isn't 'lost' in the reaction. Some of it remains as a liquid in the acid. Since the reaction is exothermic, much of the water is boiled off as steam.

Safety Precautions

The sulfuric acid and sugar reaction is a popular chemistry demonstration for high schools, colleges, and science enthusiasts. But, it isn't the kind of project you should do at home.

If you do this demonstration, use proper safety precautions. Whenever you deal with concentrated sulfuric acid, you should wear gloves, eye protection, and a lab coat. Consider the beaker a loss, since scraping burnt sugar and carbon off of it isn't an easy task. It's preferable to perform the demonstration inside of a fume hood because the reaction releases sulfur oxide vapor.

Other Exothermic Chemistry Demonstrations

If you're looking for other dramatic exothermic demonstrations, why not give one of these a try?

• Steel Wool and Vinegar : Soaking steel wool in vinegar is something you can do at home. Basically, the acetic acid in vinegar reacts with iron in the steel wool in an oxidation reaction. It's rust formation, but it occurs much more rapidly than waiting for natural processes.
• Barking Dog Reaction : This barking dog reaction gets its name for the sound it makes. Igniting a mixture of carbon disulfide and nitric oxide in a long glass tube forms a flame. The flame travels down the tube, compressing gases in front of it until they have nowhere to go and explode. The small explosion doesn't break the tube, but it does produce a loud "bark" or "woof" and it glows bright blue.
• Dissolving Laundry Detergent in Water : While not as exciting as the sulfuric acid and sugar reaction or the barking dog reaction, dissolving laundry detergent is something you can try the next time you wash your clothes. Hold a bit of dry detergent in your hand and dampen it with water. It gets warm!
• Elephant Toothpaste Demonstration : If elephants used toothpaste, it would be the size of the foam produced by this chemical reaction. The reaction between hydrogen peroxide and potassium iodide produces a lot of gas. A bit of detergent added to the mixture traps the gas and makes a steaming, bubbly foam. Adding food coloring customizes the color.
• Roesky, Herbert W. (2007). “Experiment 6: Sugar coal by splitting off water from sugar with sulfuric acid”.  Spectacular Chemical Experiments . Wiley. p. 17. ISBN 978-3-527-31865-0.
• Shakhashiri, Bassam Z.; Shreiner, Rodney; Bell, Jerry A. (2011). “1.32 Dehydration of Sugar by Sulfuric Acid”.  Chemical Demonstrations: A Handbook for Teachers of Chemistry Volume 1 . University of Wisconsin press. pp. 77–78. ISBN 978-0-299-08890-3.
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Sugar Dehydration

Convert sugar into carbon with sulfuric acid

Turn sugar into carbon by dehydrating sugar with strong sulfuric acid.

• 100 mL of 16 M sulfuric acid
• 85 g of granulated sugar

Perform demonstration in a well ventilated area.

• Add sulfuric acid to a beaker
• Add sugar to a beaker
• Stir the mixture completely
• Wait 2–3 minutes for reaction to complete
• Apparatus will be HOT. Do NOT touch until cool.

The sugar dehydration experiment (also known as the carbon snake experiment) is based on the ability of concentrated sulfuric acid to dehydrate sugar via the following process:

$$\mathrm{C_{12}H_{22}O_{11}}(g) \longrightarrow 12\mathrm{C}(s, \mathrm{~graphite}) + 11\mathrm{H_2O}(l)$$

We see sugar is converted to solid, black graphite and water is a product (hence dehydration).

When table sugar and concentrated sulfuric acid are combined, an exothermic reaction occurs that produces vaporized water and carbon dioxide. The vaporized water and carbon dioxide are responsible for the expansion of the mixture inside the container. As water and carbon dioxide are produced, the mixture becomes inflated and expands beyond the opening of its container, creating a snake-like appearance. The overall chemical equation can be seen below.

$$\mathrm{C_{12}H_{22}O_{11}}(g) + \mathrm{H_2SO_4}(aq) + \dfrac{1}{2}\mathrm{O_2}(g) \longrightarrow 11\mathrm{C}(s) + \mathrm{CO_2}(g) + 12\mathrm{H_2O}(g) + \mathrm{SO_2}(g) + \mathrm{heat}$$

If you look closely, you can see steam coming off the column of graphite!

Eric Van Dornshuld

Assistant clinical professor.

Faculty advisor to the MSU SMACS (2016–present).

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Lecture Demonstrations

• Demo 31: Carbon Snake

Carbon Snake

100 or 150-mL Beaker (tall form)

Sucrose to fill Beaker about 1/3 full

conc. (18 M) Sulfuric Acid

Glass Stirring Rod

Large Crystallization Dish for overflow

Benchcote or Large Tray for under Crystallizing Dish

Gloves and Goggles

• Add conc Sulfuric acid to beaker until it just covers the sugar and mix with the stirring rod. You may need to add a little more sulfuric acid.
• When you feel the beaker heating up, stop stirring and put the beaker down in the crystallization dish.
• The reaction takes about 5 to 8 minutes to start to fully react.
• Result should be a nice column of graphite.

Note: Do this demonstration in a well ventilated room, and stand back when it starts to react.  The fumes given off are Sulfuric Acid

Waste Management

The graphite column is saturated with sulfuric acid. It should be placed in a bucket of water and the whole thing neutralized with sodium bicarbonate. Then it can be dumped down the sink. (Alternatively just double bag  the whole thing including the beaker and give it to EH&S).

BEARDED SCIENCE GUY

How to do the sulfuric acid and sugar dehydration reaction.

YouTube Video

Watch the Sulfuric Acid and Sugar Experiment

SAFETY NOTE: Due to the nature of this experiment, it is best performed in a lab with a scientist or science educator.

Sulfuric Acid and Sugar Experiment Supply List

​Small glass container

​Granulated or powdered sugar

Concentrated sulfuric acid

Stirring stick

Don't forget your safety gear!

Safety goggles

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Instant Fire Demonstration 1

Make instant fire using sugar, potassium chlorate, and sulfuric acid. No matches or flame is needed for this exciting chemistry demonstration!

Instant Fire Materials

You only need three chemicals for this reaction:

• Potassium chlorate
• Granulated table sugar – sucrose
• Sulfuric acid

Perform the Instant Fire Demonstration

You can do this demonstration in a test tube or on a heat-safe dish. Goggles, gloves, and a lab coat are recommended. Don’t use glassware you value too highly, since there is a good chance the highly exothermic reaction will shatter it.

• Mix together roughly equal amounts of potassium chlorate and sugar.
• Add a drop or two of sulfuric acid to the mixture to start the reaction. That’s it! Expect purple flames, smoke, and heat.

How It Works

The chemical reaction for this demonstration is:

2KClO 3 (s) + heat —> 2KCl(s) + 3O 2 (g)

This is a decomposition reaction  in which potassium chlorate breaks down in potassium chloride and oxygen. Potassium chlorate is a powerful oxidizer. Adding sulfuric acid provides enough heat to accelerate the reaction. Once there is sufficient heat, the oxygen from the reaction burns, using sugar as the fuel.

Dancing Gummy Bear Variation

Another way to do this demonstration is to make a candy, such as a gummy bear , appear to dance in the flames.

• Secure a large test tube to a ring stand to hold it in place and so you’ll be able to distance yourself from it.
• Heat a small amount of potassium chlorate in a large test tube.
• Once the potassium chlorate has melted, add a gummy bear candy.

See the Instant Fire Reaction in Action

Here’s a quick video of this chemical reaction, so you can see what to expect. There are two things you’ll notice here. First, the potassium compound produces a bright purple flame, just as you would expect from a potassium flame test or bead test . Second, it’s important to use a heat-safe container and surface and proper safety gear when performing this reaction, because once it takes off, it gets exciting quickly!

More Fire Science

• Learn How Firework Color Chemistry Works
• Make a Tabletop Green Fire Tornado
• Use Sugar To Make Homemade Black Snake Fireworks

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"Carbon snake" experiment

How to make a huge black snake of sugar and sulfuric acid

A black snake crawls out of a glass of sug­ar when con­cen­trat­ed sul­fu­ric acid is added to it.

Reagents and equip­ment:

• con­cen­trat­ed sul­fu­ric acid;
• beaker (50 ml).

Step-by-step in­struc­tions

Fill a beaker ap­prox­i­mate­ly two thirds full of sug­ar . Add 10-15 ml of con­cen­trat­ed sul­fu­ric acid. Af­ter a while a black col­umn of prod­ucts of the de­hy­dra­tion and ox­i­da­tion of sug­ar be­gin to come out of the glass.

Pro­cess­es de­scrip­tion

Ow­ing to its de­hy­drat­ing and ox­i­diz­ing abil­i­ty, sul­fu­ric acid caus­es the break­down and car­boniza­tion of sug­ar. The mix­ture heats up, and wa­ter va­por and car­bon diox­ide are re­leased. This leads to the prod­ucts of the break­down of sug­ar be­ing pushed out of the glass. As soon as they make con­tact with air , they cool and hard­en.

Safe­ty pre­cau­tions

The re­ac­tion mix­ture heats up in­tense­ly – avoid burns! Make sure sul­fu­ric acid doesn’t get on your skin or clothes. Wear pro­tec­tive glass­es and gloves. The ex­per­i­ment should be car­ried out in a fume hood or well-ven­ti­lat­ed room. Fol­low gen­er­al safe­ty rec­om­men­da­tions. Chem­i­cal ex­per­i­ments must be car­ried out in full com­pli­ance with the leg­is­la­tion of your coun­try.

Warn­ing! Only un­der pro­fes­sion­al su­per­vi­sion.

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