“Jumping sodium” experiment

Ноw to make sodium jump

An ex­pe­ri­enced chemist can syn­the­size a sub­stance, car­ry out a re­ac­tion, and… make sodi­um “jump”! In this ex­per­i­ment we will look at one of the main prop­er­ties of al­ka­line met­als – the re­ac­tion with wa­ter.

Reagents and equip­ment:

  • wa­ter (60 ml);
  • kerosene (40 ml);
  • 1% so­lu­tion of thy­molph­thalein;
  • metal­lic sodi­um;
  • 2 mea­sur­ing ves­sels.

Step-by-step in­struc­tions

  1. Pour 30 ml of wa­ter into each mea­sur­ing cylin­der.
  2. Add a few drops of the so­lu­tions of the thy­molph­thalein and phe­nolph­thalein in­di­ca­tors to the wa­ter.
  3. Pour 20 ml of kerosene into each mea­sur­ing cylin­der. Two lay­ers form of liq­uids that do not mix.
  4. Cut a piece of metal­lic sodi­um and add it to each ves­sel.

First the sodi­um pass­es through the lay­er of kerosene, with which it does not re­act. When the sodi­um con­tacts the lay­er of wa­ter, a vi­o­lent re­ac­tion takes place with the re­lease of gas and grad­u­al col­or­ing of the low­er lay­er of liq­uid. The piece of sodi­um be­gins to jump con­stant­ly be­cause of the gas re­leased.

Pro­cess­es de­scrip­tion

Kerosene and wa­ter have dif­fer­ent den­si­ty and do not mix to­geth­er. Sodi­um does not re­act with kerosene, but re­acts with wa­ter, form­ing an al­ka­li (sodi­um hy­drox­ide) and hy­dro­gen:

2Na + 2H₂O = 2NaOH + H₂

Gas bub­bles push the sodi­um into the lay­er of kerosene, but due to the force of grav­i­ty the sodi­um sinks back to the lay­er of wa­ter. Thus, sodi­um seems to jump in the lay­er of kerosene! It will jump like this un­til it has re­act­ed com­plete­ly with the wa­ter.

Sodi­um hy­drox­ide, which forms in the re­ac­tion, changes the acid­i­ty of the medi­um of the low­er lay­er of liq­uid. The in­di­ca­tors re­act to this change, turn­ing the low­er lay­er a cer­tain col­or. Thy­molph­thalein turns blue, and phe­nolph­thalein turns deep pink.

Safe­ty pre­cau­tions

This ex­per­i­ment must be car­ried out in pro­tec­tive gloves and glass­es, ob­serv­ing safe­ty rules in work­ing with flammable sub­stances. Metal­lic sodi­um ig­nites on con­tact with wa­ter, so it is stored in jars with thick glass walls un­der a lay­er of kerosene. The un­re­act­ed re­mains of sodi­um must be de­stroyed by dis­solv­ing them in ethanol. They must not be flushed down the drain.

Warn­ing! Don’t try to re­peat this ex­per­i­ment with­out a pro­fes­sion­al su­per­vi­sion!