Weird Science

Zinc and Sulfur: A Reaction That Sparks

Polish ver­sion is here

Vio­lent Reac­tion

Zinc is a tran­s­i­tion metal that was disco­ve­red in ancient India or China but did not reach Europe until the 17th cen­tury. It is a soft, brit­tle metal with a blu­ish-white color.

Ilustracja

Source: http://upload.wiki­me­dia.org/wiki­pe­dia/com­mons/f/f9/Zinc_frag­ment_sub­li­med_and_1cm3_cube.jpg, acces­sed: 04/15/2012

Sul­fur, on the other hand, is a non­me­tal. This ele­ment has seve­ral allo­tro­pic forms, the three most impor­tant being rhom­bic, monoc­li­nic, and amor­phous sul­fur. It is a yel­low cry­stal­line sub­stance that is rela­ti­vely brit­tle under nor­mal con­di­tions.

Ilustracja

Source: http://upload.wiki­me­dia.org/wiki­pe­dia/com­mons/4/44/Sul­fur-sam­ple.jpg, acces­sed: 04/15/2012

Zinc and sul­fur have a strong che­mi­cal affi­nity for each other and rea­dily react with each other. The reac­tion between these two ele­ments is highly exo­ther­mic and extre­mely rapid, pro­du­cing an impres­sive visual effect.

Requ­i­red Sub­stan­ces

As you might have gues­sed, we will need just two sub­stan­ces:

Both zinc and sul­fur must be finely pow­de­red. Sul­fur can be easily gro­und using a mor­tar and pestle.

War­ning: This reac­tion is extre­mely vigo­rous, so pro­tec­tive gog­gles must be worn at all times! The pow­de­red zinc-sul­fur mixture sho­uld never be sto­red! The expe­ri­ment must be con­duc­ted under a fume hood or out­do­ors. The author assu­mes no respon­si­bi­lity for any dama­ges that may occur. You pro­ceed at your own risk!

Pro­ce­dure

Care­fully mix pow­de­red zinc and sul­fur in a 2:1 wei­ght ratio. A small por­tion of the mixture (about 3-4 grams / 0.1-0.14 oz) sho­uld be sha­ped into a small cone on a non-flam­ma­ble sur­face, such as a cera­mic, asbe­stos-free fire­proof board, or metal plate. It is best to con­duct the reac­tion out­do­ors due to the large amo­unt of smoke pro­du­ced. To ini­tiate the reac­tion, hea­ting is requ­i­red. A sim­ple and effec­tive igni­tion method is a pyro­tech­nic fuse. A home­made fuse can be made by soa­king a strip of fil­ter paper in potas­sium chlo­rate(V) solu­tion and allo­wing it to dry. The effect of the expe­ri­ment can be seen in the video below:

The reac­tion lasts only a frac­tion of a second, pro­du­cing a burst of gre­e­nish-yel­low fla­mes along with a large cloud of smoke. A sharp, crac­kling sound accom­pa­nies the reac­tion. In addi­tion to the smoke, a fine layer of zinc sul­fide is for­med, which set­tles as a light dust. Due to the very short dura­tion of the fire­ball, cap­tu­ring it in a pho­to­graph can be chal­len­ging. Never­the­less, below are two snap­shots of the effect:

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During the reac­tion, a spec­ta­cu­lar fire­ball often forms, resem­bling a mush­room cloud. This effect is extre­mely brief and is best obse­rved when per­for­ming the expe­ri­ment in the dark. Below are frame-by-frame slow-motion ima­ges cap­tu­ring this phe­no­me­non:

Ilustracja

Expla­na­tion

From a che­mi­cal per­spec­tive, this is a sim­ple syn­the­sis reac­tion. Upon local hea­ting, zinc reacts with sul­fur accor­ding to the equ­a­tion:

Ilustracja

This reac­tion is highly exo­ther­mic, so once ini­tia­ted, it susta­ins itself without any addi­tio­nal heat input.

Enjoy!

Fur­ther rea­dings:

Marek Ples

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