What do marble, chalk, and eggs have in common?

Properties and application of calcium carbonate

Safe­ty pre­cau­tions

Wear pro­tec­tive gloves, a mask, and safe­ty glass­es. Work in a well-ven­ti­lat­ed area. Ob­serve safe­ty mea­sures when work­ing with fire and hot ob­jects.

Reagents and equip­ment

Syn­the­siz­ing cal­ci­um car­bon­ate:

  • 0.17% cal­ci­um hy­drox­ide so­lu­tion;
  • car­bon diox­ide;
  • a test tube.

Dis­solv­ing cal­ci­um car­bon­ate (mar­ble):

  • cal­ci­um car­bon­ate (mar­ble);
  • 10% hy­drochlo­ric acid so­lu­tion;
  • a beaker.

Rub­ber egg ex­per­i­ment:

  • chick­en or quail eggs;
  • 9% acetic acid so­lu­tion (vine­gar);
  • a glass.

Flammable gel ex­per­i­ment:

  • 50 g crushed eggshell;
  • 50 mL 70% acetic acid so­lu­tion;
  • 60 mL wa­ter;
  • 150 mL 96% ethyl al­co­hol;
  • a glass;
  • a wood­en stick;
  • a lid that fits the glass;
  • a glass con­tain­er.

Glow­ing mar­ble:

  • mar­ble;
  • a blow­torch;
  • a heat-re­sis­tant work sur­face;
  • metal­lic tweez­ers.

Step-by-step in­struc­tions

Syn­the­siz­ing cal­ci­um car­bon­ate:

Bub­ble car­bon diox­ide through a 0.17% cal­ci­um hy­drox­ide so­lu­tion. Watch as the so­lu­tion be­comes cloudy.

Dis­solv­ing cal­ci­um car­bon­ate (mar­ble):

Place a piece of cal­ci­um car­bon­ate (mar­ble) in a beaker and add a 10% hy­drochlo­ric acid so­lu­tion. Watch the re­sult­ing vig­or­ous re­lease of gas.

Rub­ber egg ex­per­i­ment:

Place an egg in a glass and add a 9% acetic acid so­lu­tion (vine­gar). Leave it there un­til the eggshell dis­solves com­plete­ly, at least six hours. The du­ra­tion of this ex­per­i­ment will de­pend heav­i­ly on the thick­ness of the shell. Take the egg out of the glass and rinse it thor­ough­ly with wa­ter. Note that the shell has dis­solved, and the egg has be­come rub­bery.

Flammable gel ex­per­i­ment:

Pour 50 g of crushed eggshell into a glass and add 50 mL of 70% acetic acid so­lu­tion. Now add 30 mL of wa­ter. Close with a lid and leave for a week — be sure to keep away from chil­dren and an­i­mals. A week lat­er, add 30 mL of wa­ter and mix thor­ough­ly. Fil­ter the re­sult­ing so­lu­tion through a fun­nel with cot­ton wool. Pour the so­lu­tion into a bowl and add 100 mL of ethyl al­co­hol. In sev­er­al sec­onds, the so­lu­tion will turn into gel.

Glow­ing mar­ble:

Heat a piece of mar­ble with a blow­torch. When you stop heat­ing the stone, you should see it glow­ing. Con­duct this ex­per­i­ment in a dark­ened room.

Process de­scrip­tion

Syn­the­siz­ing cal­ci­um car­bon­ate:

When car­bon diox­ide is bub­bled through a cal­ci­um hy­drox­ide so­lu­tion, it pro­duces cal­ci­um car­bon­ate, which dis­solves poor­ly in wa­ter and there­fore pre­cip­i­tates out. Ca(OH)₂ + CO₂ = Ca­CO₃ + H₂O

Dis­solv­ing cal­ci­um car­bon­ate (mar­ble):

Cal­ci­um car­bon­ate re­acts with hy­drochlo­ric acid, form­ing un­sta­ble car­bon­ic acid, which dis­so­ci­ates into car­bon diox­ide gas and wa­ter: Ca­CO₃ + 2HCl = Ca­Cl₂ + CO₂ + H₂O

Rub­ber egg ex­per­i­ment:

An eggshell con­tains cal­ci­um car­bon­ate, which dis­solves read­i­ly in vine­gar with a re­lease of car­bon diox­ide: СаСО₃ + 2СН₃СООН = Са(СН₃СОО)₂ + СО₂ + Н₂О Only a thin film is left at the end. This film keeps the egg from leak­ing out and turns it into some­thing re­sem­bling a ball!

Flammable gel ex­per­i­ment:

If you add ethyl al­co­hol to the cal­ci­um ac­etate so­lu­tion pro­duced by dis­solv­ing an eggshell in acetic acid, it will form a flammable gel that can be used as a sol­id fuel. The gel forms via the sol­va­tion of cal­ci­um ions by ethyl al­co­hol mol­e­cules, a process in which the mol­e­cules of ethyl al­co­hol sur­round the cal­ci­um ions from all sides. Such a gel should be stored in an air­tight con­tain­er to pre­vent the al­co­hol from evap­o­rat­ing.

Glow­ing mar­ble: Mar­ble in the Earth’s crust re­ceives small dos­es of en­er­gy, such as small amounts of ra­di­a­tion. Though this ra­di­a­tion doesn’t make the mar­ble ra­dioac­tive, it pro­vides ad­di­tion­al en­er­gy to atoms in the mar­ble’s struc­ture, and some elec­trons in these atoms re­main in an ex­cit­ed (un­sta­ble) state. When heat­ed, mar­ble re­leas­es this en­er­gy with a vis­i­ble glow.

Ap­pli­ca­tions

  • Cal­ci­um car­bon­ate is also used to re­fine sug­ar. In a pre­pared sug­ar syrup, cal­ci­um car­bon­ate par­ti­cles ad­here to im­pu­ri­ties and pre­cip­i­tate down to the bot­tom.
  • In the med­i­cal in­dus­try, cal­ci­um car­bon­ate is used to treat the ex­ces­sive acid­i­ty of gas­tric juices. It neu­tral­izes the hy­drochlo­ric acid found in the stom­ach
  • Mixed with wa­ter, cal­ci­um car­bon­ate is used as a paint, some­times known as "whit­ing."
  • It is in­clud­ed as an abra­sive com­po­nent in nu­mer­ous house­hold clean­ing pow­ders.
  • Cal­ci­um car­bon­ate can be harm­ful as well – it is found in the scale that forms in wa­ter heaters be­cause of hard wa­ter.
  • Due to its soft­ness, cal­ci­um car­bon­ate in the form of chalk is of­ten used for writ­ing and draw­ing.
  • The hard­ness of mar­ble, which is also cal­ci­um car­bon­ate, found use in sculp­ture. For in­stance, the Lin­coln Memo­ri­al in Wash­ing­ton, D.C. is made of mar­ble.
  • The skele­tons of stony corals con­sist al­most en­tire­ly of cal­ci­um car­bon­ate.
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