“Christmas tree decoration” experiment

How to make a silvery decoration with a glass flask

Chemists have a very fine­ly de­vel­oped sense of beau­ty, they not only do sci­en­tif­ic work, but they can also make Christ­mas tree dec­o­ra­tions! Us­ing the sil­ver mir­ror re­ac­tion, we can make shiny and fes­tive cones that you can hang on the Christ­mas tree!

Safe­ty pre­cau­tions

Be­fore start­ing the ex­per­i­ment, put on pro­tec­tive gloves and a lab coat. If sil­ver ni­trate gets on the skin, im­me­di­ate­ly rinse it with an abun­dant quan­ti­ty of wa­ter.

Reagents and equip­ment:

  • sil­ver ni­trate so­lu­tion 100 ml 5 g/l;
  • sodi­um hy­drox­ide so­lu­tion 5 ml 5 g/l;
  • am­mo­nia so­lu­tion 3% 5 ml;
  • glu­cose so­lu­tion 30 ml 5 g/l, glass flasks, rib­bon, fir tree twig

Step-by-step in­struc­tions

Take a glass flask–it will be the body for the dec­o­ra­tion. Pour a sil­ver ni­trate so­lu­tion into it and add the sodi­um hy­drox­ide so­lu­tion drop by drop. Then add drops of the am­mo­ni­um so­lu­tion un­til the sed­i­ment dis­solves. Then pour the glu­cose so­lu­tion into the flask and shake in­ten­sive­ly for 3-5 min­utes. Af­ter a few min­utes, a shiny met­al film will form on the walls of the flask. Pour out the con­tents of the flask and rinse sev­er­al times with dis­tilled wa­ter. Dec­o­rate the flask with a fir tree twig and a satin rib­bon.

Pro­cess­es de­scrip­tion

The ba­sis of mak­ing the dec­o­ra­tions is the qual­i­ta­tive re­ac­tion to alde­hy­des, which is called the “Sil­ver mir­ror re­ac­tion”. When sil­ver ni­trate re­acts with sodi­um hy­drox­ide, brown sil­ver ox­ide forms:

2Ag­NO₃ + 2NaOH → Ag₂O + 2NaNO₃ + H₂O

In the aque­ous so­lu­tion of am­mo­ni­um, sil­ver ox­ide dis­solves with the for­ma­tion of the com­plex com­pound of di­ammi­ne­sil­ver(I) hy­drox­ide [Ag(NH₃)₂]OH], which chemists com­mon­ly call Tol­lens’ reagent:

Ag₂O + 4N­H₄OH => 2[Ag(NH₃)₂]OH + Н₂O

Glu­cose is an alde­hyde al­co­hol, i.e. it con­tains al­co­hol and alde­hyde groups, and the lat­ter is a re­duc­er. When glu­cose is added to the ob­tained so­lu­tion, sil­ver is re­duced from the so­lu­tion, and on the sur­face of the glass a shiny met­al film forms:

НОСН₂(СНОН)₄HС=O + 2[Ag(NH₃)2]OH => НОСН₂(CHОН)₄СООH + 2Ag +3NH₃ + H₂O