The violent reaction of sodium and water: experiment wisely

Chem­i­cal ex­per­i­ments are di­verse in their depth, com­plex­i­ty and ef­fec­tive­ness. Any list of the most im­pres­sive ex­per­i­ments must in­clude the “pharaoh’s snake” or the in­ter­ac­tion of snake poi­son with hu­man blood. But chemists also like to try more dan­ger­ous ex­per­i­ments, one of which is the re­ac­tion of wa­ter and sodi­um.

Abil­i­ties of sodi­um

Sodi­um is an ex­treme­ly ac­tive met­al which en­ters into a re­ac­tion with many well-known sub­stances. The re­ac­tion with sodi­um of­ten takes place vi­o­lent­ly, ac­com­pa­nied by a con­sid­er­able re­lease of heat, com­bus­tion and some­times even ex­plo­sions. Work­ing safe­ly with the sub­stance re­quires a pre­cise un­der­stand­ing of its phys­i­cal and chem­i­cal char­ac­ter­is­tics.

Sodi­um is not very hard in its struc­ture, and is dis­tin­guished by the fol­low­ing char­ac­ter­is­tics:

• low den­si­ty (0.97 g/cm³);
• soft­ness;
• low melt­ing point (97.81 °С).

The met­al, which ox­i­dizes swift­ly in air, should be stored in sealed con­tain­ers un­der a lay­er of Vase­line or kerosene. Be­fore con­duct­ing the ex­per­i­ment with sodi­um and wa­ter, cut off a piece of sodi­um with a fine scalpel, re­move the piece from the con­tain­er with tweez­ers and thor­ough­ly clean the kerosene from it with fil­ter pa­per.

Warn­ing! All the tools must be dry!

You must wear pro­tec­tive glass­es when work­ing with the met­al, as the small­est care­less step may lead to an ex­plo­sion.

The re­ac­tion of wa­ter and sodi­um: a his­to­ry of study­ing ex­plo­sions

The re­ac­tion of wa­ter and sodi­um was first stud­ied by sci­en­tists at the Czech Acad­e­my of Sci­ences un­der the lead­er­ship of Pavel Jung­wirth. The ex­per­i­ment of the det­o­na­tion of sodi­um and wa­ter, which had been known since the 19th cen­tu­ry, was thor­ough­ly an­a­lyzed and de­scribed.

The re­ac­tion of sodi­um and wa­ter in­volved im­mers­ing a piece of the met­al in or­di­nary wa­ter, and gave am­bigu­ous re­sults: some­times there was an ex­plo­sion, some­times there was none. Lat­er the rea­son for the dif­fer­ing re­sults was found – the in­sta­bil­i­ty was caused by the sizes and forms of the pieces of sodi­um used.

The greater the di­men­sions of the met­al, the more pow­er­ful and dan­ger­ous the re­ac­tion of sodi­um and wa­ter be­came.

A slow-mo­tion film of the process of in­ter­ac­tion showed that five mil­lisec­onds af­ter the sodi­um was im­mersed in wa­ter, the met­al “shriv­eled”, re­leas­ing hun­dreds of “nee­dles”. The met­al elec­trons that in­stan­ta­neous­ly en­tered the wa­ter lead to an ac­cu­mu­la­tion of a pos­i­tive charge in the met­al: the re­pul­sion of pos­i­tive par­ti­cles tears up the met­al, caus­ing the “nee­dles” to ap­pear. At the same time, the area of the met­al in­creas­es, which is what caus­es such a vi­o­lent re­ac­tion.

Here you’ll find safe and en­ter­tain­ing ex­per­i­ments with sodi­um com­pounds.

The re­ac­tion of sodi­um and wa­ter in the lab­o­ra­to­ry

It is easy to re­al­ize the re­ac­tion of wa­ter and sodi­um in the lab­o­ra­to­ry. Fill a crys­tal­liz­er three quar­ters full of wa­ter, and add sev­er­al drops of phe­nolph­thalein. Throw a piece of sodi­um the size of half a pea into the re­sult­ing mix­ture.

The al­ka­line met­al im­me­di­ate­ly en­ters into a re­ac­tion, and the heat caus­es the sodi­um to melt, turn­ing into a “sil­very” drop, which moves swift­ly over the sur­face of the wa­ter, mak­ing hiss­ing nois­es.

In the course of the re­ac­tion, an al­ka­li will form, leav­ing a crim­son trail be­hind the piece of sodi­um. At the end of the ex­per­i­ment, prac­ti­cal­ly all the wa­ter in the crys­tal­liz­er will have turned a crim­son shade.

The re­ac­tion of wa­ter and sodi­um re­quires the sci­en­tist to ob­serve all safe­ty mea­sures strict­ly: wear pro­tec­tive glass­es, and try to stay at a cer­tain dis­tance from the crys­tal­liz­er. Even the small­est er­rors may lead to an ex­plo­sion. It is dan­ger­ous for the tini­est par­ti­cle of sodi­um or al­ka­li to get in the eyes.

Warn­ing! Don’t try to re­peat these ex­per­i­ments with­out a pro­fes­sion­al su­per­vi­sion!