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The very name DRY ICE sounds a lit­tle strange, doesn’t it? We’re used to ice melt­ing rapid­ly and turn­ing into or­di­nary wa­ter… But here it’s all a lot more com­pli­cat­ed. Yes, dry ice is ac­tu­al­ly gas! So this ice doesn’t melt, but sub­limes – it moves right from a sol­id state to a gaseous state! In this ex­per­i­ment, we ex­am­ine dif­fer­ent phys­i­cal and chem­i­cal prop­er­ties of dry ice.

Safe­ty pre­cau­tions

Use gloves and nev­er let dry ice touch the skin for a long pe­ri­od of time. It has a tem­per­a­ture of -78,5 С, and you may re­ceive a cold burn. Try not to breathe in CO2 gas – it may cause headaches.

Warn­ing! Sub­stances of this ex­per­i­ment are tox­ic and high­ly dan­ger­ous for your health. Do not try this at home. Only un­der pro­fes­sion­al su­per­vi­sion.

Reagents and equip­ment:

* dry ice;
* dis­tilled wa­ter;
* liq­uid soap;
* thy­molph­thalein;
* phe­nolph­thalein;
* lit­mus;
* glass bowl;
* 3 beakers.

Step-by-step in­struc­tions

Take a piece of dry ice and place it on a met­al spoon. Af­ter a few sec­onds, it will start to jump and shake. Then put the dry ice in the glass bowl with wa­ter and ob­serve the vi­o­lent re­lease of gas bub­bles and white smoke. If you add a few drops of dish-wash­ing liq­uid to the wa­ter, then a thick foam of soap bub­bles full of white smoke ap­pears. Then take 3 beakers with in­di­ca­tor so­lu­tions: in­di­go carmine – a so­lu­tion of an in­di­go col­or, phe­nolph­thalein, which is col­or­less, and lit­mus, of a red-or­ange col­or.

Then add a lit­tle sodi­um hy­drox­ide, and the so­lu­tions change their col­or: the in­di­go carmine turns green, the phe­nolph­thalein turns crim­son, and the lit­mus turns blue. Add sev­er­al pieces of dry ice to each beaker. Af­ter a while, ob­serve the so­lu­tions change back to their orig­i­nal col­or.

Pro­cess­es de­scrip­tion

Dry ice is a very sim­ple sub­stance, the sol­id phase of CO₂. It is wide­ly avail­able and used to trans­port food prod­ucts or clean in­dus­tri­al sur­faces. But in the home lab­o­ra­to­ry, dry ice be­comes an in­valu­able source of ex­per­i­ments. The trick of dry ice lies in the fact that it moves im­me­di­ate­ly from a sol­id phase to a gas phase, with­out an in­ter­me­di­ary liq­uid phase (this process is known as sub­li­ma­tion). The tem­per­a­ture of the sub­li­ma­tion of car­bon diox­ide is -78,5°С.

On con­tact with wa­ter, dry ice starts to trans­form vi­o­lent­ly from a sol­id phase to a gas phase, which looks like boil­ing, only with a much more pro­nounced for­ma­tion of steam. The car­bon diox­ide that evap­o­rates is heav­ier than air (a den­si­ty of 1.9768 kg/m3 as op­posed to 1.225 kg/m³), and so the “smoke” set­tles on the sur­face, sur­round­ing the con­tain­er of wa­ter, and does not rise.

When liq­uid soap is added, the bub­bles of the re­leased gas quick­ly cause it to froth, and a thick foam filled with white car­bon diox­ide gas forms.

If you place dry ice on a met­al sur­face, it will jump and shake. This hap­pens be­cause the met­al sur­face is warm, and the dry ice sub­limes very quick­ly on its sur­face, form­ing sources of high pres­sure, which caus­es the piece of dry ice to jump.

In the sub­li­ma­tion of dry ice in wa­ter, the car­bon diox­ide re­leased re­acts with wa­ter, form­ing car­bon­ic acid and chang­ing the acid­i­ty. This prop­er­ty of dry ice can be used for im­pres­sive col­or­ful trans­for­ma­tions with in­di­ca­tor so­lu­tions. The in­di­ca­tor so­lu­tion of in­di­go carmine is blue in a neu­tral medi­um, phe­nolph­thalein is col­or­less, and lit­mus is red-or­ange.

When sodi­um hy­drox­ide is added, the medi­um be­comes al­ka­line, and the so­lu­tions change their col­ors to green, crim­son and blue re­spec­tive­ly. When pieces of dry ice are added to the al­ka­line so­lu­tion, car­bon­ic acid forms, the acid­i­ty of the so­lu­tions ris­es, the medi­um be­comes neu­tral and the so­lu­tions re­turn to their orig­i­nal col­ors.

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