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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. Here's a nice youtube video for you, if you'd like to see what to expect.

What Happens
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.

C12H22O11 (sugar) + H2SO4 (sulfuric acid) → 12 C (carbon) + 11 H2O (water) + mixture water and acid

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
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. After the beaker has cooled, you can pull out the carbon and remove the residue from the glassware with acetone. It's preferable to perform the demonstration inside of a fume hood.

More Ways to Make Black Snakes | Sulfuric Acid and Water

Comments

February 4, 2008 at 11:57 am
(1) William says:

The “black tom” explosion in WW1 at New York was, people say, triggered by gadgets using a variation on this -

July 28, 2008 at 1:36 am
(2) Geoff waters says:

The UTube demonstration of this experiment displays woeful lack of safety features in handling conc. sulphuric acid. Here in Melbourne (Victoria, Australia) safe working procedures are integral to science content. The protective equipment in this video is
inadequate: open lab coat cuffs (need long gauntlet gloves ore sleeeve protectors), the gloves are too flimsy, and overall too much unneccessary handling of the materials. The demo. works perfectly well if the acid is added to dry sugar, and allowed to progress over 3-4 minutes.

March 4, 2010 at 3:57 pm
(3) Nat Sternbergh says:

How does this equation balance? In the science class I work in, the eighth graders watched the teacher do this reaction (I’m an aide).
The reaction as you described it above doesn’t balance. Where does the sulfur go? And is the acid you mention unreacted sulfuric acid?
I’m trying to show the students how what goes in must come out in balancing, but I can’t get it to work with this reaction. I’m getting huge coefficients, and adding things like an extra pair of oxygens at the front and a bunch at the back, but that doesn’t seem right.
I can’t figure it out.
Thanks,

Nat

March 20, 2010 at 1:01 am
(4) Chem Student says:

If you consider the dehydratation, the sulfuric acid reacts with the water molecules deprotonizing, and the result, as the article states, is a mixture of water and acid (that being, a sulfuric acid solution.

The dehydratation can be writen as an equilibrium (sugar carbon + water), and the acid hydrolisis as a second equilibrium (2 H2O + H2SO4 2 H3O+ + SO4 2-). The second step consumes as much water as it can, thus favoring the dehydratation.

This explains the formation of the black solid, however it fails to explain why it foams up. The simplest explanation would be the boiling water as a result of the heat the sulfuric acid hydrolisis gives. Oxidation of some of the charcoal to CO2 (and the subsequent reduction of H2SO4 to SO3 or SO2) could also explain the formation of gases.

September 21, 2010 at 7:47 am
(5) Paul says:

What kind of gases are released from this reaction?

December 18, 2010 at 12:17 pm
(6) bryan says:

chemistry is the hardest lesson

July 23, 2011 at 11:30 pm
(7) chris says:

I never got past grade 10 chemistry…

July 24, 2011 at 1:21 am
(8) power of attorney says:

I hear ya Chris! The only thing I remember about Chemistry class is a few of the items on the Periodic Table. Gold is AU for example, etc. The experiments were fun though!

April 4, 2011 at 4:58 am
(9) Alex says:

What are the energy volumes produced. This is a highly exothermic reactions – how much power for 1kg sugar?

August 18, 2011 at 8:40 pm
(10) Olive says:

My Physical Science teacher did this in class on the first day. He did not take any saftey percautions… He only has 8 and a half fingers due to a previous dangerous Chemistry experiment.

November 9, 2011 at 8:00 pm
(11) George says:

is this a physical or chemical change?

December 8, 2011 at 8:02 pm
(12) Anonymous says:

hmmm… i wonder… if u r in 7th grade or higher i think u shud know what a chem and phys change is… DUH CHEMICAL!!!!

February 6, 2012 at 3:05 am
(13) Avvi says:

The chemical equation for Sugar is actuallt C6 H12 O6 and the equation still does not balance out. It is best to add the acid to dry sugar and leave it for 1-2 minutes.

February 22, 2012 at 6:52 pm
(14) Erik says:

Actually table sugar is sucrose, that is why the formula is C12H22O11

February 23, 2012 at 10:28 pm
(15) Russ says:

Avvi, you got roasted. Nice get, Erik. In fact you can do the experiment with glucose but the reaction is nowhere near as dramatic as when you use a disaccharide. The glucose turns dark yellow then black, but there is no “black foaming snake.”

Don’t be so rash as to disregard the gas. Sulfure dioxide can lead to respiratory problems and the water vapor produced is fairly acid. A fume hood is preferrable, but you should use a bell jar at the very least or do this experiment outside.

March 14, 2012 at 7:34 pm
(16) Patrick says:

what does the carbon tower feel like? Is it squishy?

May 2, 2012 at 5:58 pm
(17) Luke says:

What concentration of Sulfuric acid do I need? If I were to buy say, 44% sulfuric acid and 56% whatever, would the reaction take place, even if the other chemicals acted as a catalyst?

May 3, 2012 at 3:07 am
(18) Rachel says:

Am I right in thinking the equation for table sugar would be; C12H22O11 + H2SO4 –> 12C + 12H2O + SO3, and the equation for glucose would be; 12(CH2O) + H2SO4 –> 12C + 13H2O + SO3?

June 12, 2012 at 12:07 pm
(19) Alan says:

If you need to have a balanced formula I got this one here should be working,

C 6 H 2 SO 4 (catalyst) + C 12 H 22 O 11 → 12 C + 11 H 2 O + heat and H 2 O + SO 3 (gas)

However we need to consider sugar molecules does not exist in pure C 6 H 12 O 6, but are in the form of C 6 H 12 O 6 . H 2 O therefore the unbalanced equations only serve the purpose of explaining what happened rather than focusing in analytical chemical calculation.

Here in the bottom in sucrose solution section there are some nice photo of how water molecules hug the sucrose molecule
http://csi.chemie.tu-darmstadt.de/ak/immel/graphics/gallery/sucroses.html

Hope this helps.

June 12, 2012 at 12:13 pm
(20) Alan says:

Oops equation is
H 2 SO 4 (catalyst) + C 12 H 22 O 11 → 12 C + 11 H 2 O + heat and H 2 O + SO 3 (gas)

SO3 because if the heat

My bad, typeing on phone is so hard, sorry

July 22, 2012 at 9:32 am
(21) Cellular respiration says:

I am very happy to write comment on this blog because it was very helpful for me. I really thank you people for doing such a great work. Thanks a lot

September 3, 2012 at 1:14 pm
(22) IA question says:

I see what happens in this reaction, yet i dont know what you would actually measure for data for a independent and dependent variable?

November 27, 2012 at 11:27 pm
(23) not a doctor says:

we just did this experiment outside in the cold in pajamas and bullet proof glasses…nailed it

December 6, 2012 at 5:54 pm
(24) Mr. Nash says:

The beakers aren’t a loss. I did this demo 8 times today in the fume hood with small 100ml beakers. When they were cool, the carbon could be carefully pulled out as one piece. As for the black residue, fill the beaker with acetone and let soak for a few minutes. (Reuse the acetone by pouring it into the next beaker and so on). The beaker can then easily be cleaned with soap, water, and a beaker brush.

March 27, 2013 at 5:29 pm
(25) Michael says:

The sulfuric acid is a catalyst in this reaction. You would have the same amount of sulfuric acid in the end as you did in the beginning, unless some of it decomposes because of the heat created by the reaction. The sulfuric acid should not be in the balanced reaction at all, even though it is necessary for the reaction to occur.

C12H22O11 —> 12C + 11H2O

May 23, 2013 at 5:15 am
(26) Marco says:

Rachel, Alan, guys,
Why SO3? The sulfuric acid is very stable compound if there is no reducer nearby. It cannot break down to SO3 and water, at least not below 300 C, even above that it decomposes slowly. SO3 and H2O “attract” each other very strongly.
Rather, the acid (already diluted to some extent) oxidises the carbon to carbon dioxide and gives off sulphur dioxide. Sulphur dioxide can be smelled (smell of lighted match). Actually, the gases can be readily detected if you performed reaction of hot concentrated H2SO4 with carbon (coal) within a test tube with a cap, a small glass pipe going through the cap – so you could find that, for example, the gas does react with Br2 (aqueous solution), and also causes limewater to precipitate CaCO3 (and possibly CaSO3).
So, the equations should look something like
C12H22O11 -> 12 C + 11 H2O (as Michael (25) showed)
H2SO4 + H2O -> H3O(+) + HSO4(-) + heat
2 H2SO4 + C -> CO2 + 2 SO2 + 2 H2O
Of course, the odour of caramel cannot be described by these equations. There are additional intermediate steps that are going on, but the final result should be this.

October 10, 2013 at 10:41 am
(27) Rei says:

May I know what principle from TEK (thermodynamic, equilibrium and kinetic) is behind this experiment and why?

October 18, 2013 at 11:22 am
(28) Trygve says:

C12H22O11(s) + H2SO4(aq) + 1/2 O2(g) → 11C(s) + CO2(g) + 12H2O(g) + SO2(g)
You’re welcome ;)

October 21, 2013 at 7:13 am
(29) tahereh says:

Hi…would you mention about the minimum concentration of acid, for reaction to take place?

November 15, 2013 at 9:12 am
(30) HomeChemist says:

Minimum concentration depents on the temperature of sulfuric acid. Rapid reaction happens with 90% H2SO4.

February 13, 2014 at 1:45 pm
(31) kharlhebb says:

wow..dats gr8. both da post n da comments have really helped me a lot,in ma tight chem.asignment in undastandin da whole concept..i fink mre of dz wil b deeply appreciatd..tnx

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