"Dry chemistry" experiment

How to make salts change their color without any liquid

We’re all used to chem­i­cal re­ac­tions tak­ing place in so­lu­tions or in a gaseous state, but this is not al­ways the case. In this col­or­ful ex­per­i­ment we car­ry out a chem­i­cal re­ac­tion us­ing dry sub­stances.

Reagents and equip­ment:

  • cop­per(II) chlo­ride di­hy­drate;
  • cobalt (II) chlo­ride hex­ahy­drate;
  • potas­si­um thio­cyanate;
  • 2 ce­ram­ic cups;
  • pes­tle for grind­ing.

Step-by-step in­struc­tions

In the ce­ram­ic cups, mix potas­si­um thio­cyanate with cop­per (II) chlo­ride di­hy­drate and cobalt (II) chlo­ride hex­ahy­drate, and grind.

Pro­cess­es de­scrip­tion

There’s a whole branch of an­a­lyt­i­cal chem­istry called “Dry chem­istry”. When cer­tain sub­stances are ground to­geth­er, char­ac­ter­is­tic col­ored com­pounds form. In this ex­per­i­ment, when potas­si­um rho­danide is ground with cop­per (II) chlo­ride di­hy­drate, dark grey cop­per (II) thio­cyanate forms. When potas­si­um rho­danide is ground with cobalt (II) chlo­ride hex­ahy­drate, blue-pur­ple tetrarho­danocobal­tate (II) forms. We should note that the ini­tial salts con­tain crys­tal­lized wa­ter, so the re­ac­tion par­tial­ly takes place in a so­lu­tion.

2KSCN + Cu­Cl₂∙2H₂O → Cu(SCN)₂ + 2KCl + H₂O

Co­Cl₂∙6H₂O + 4KSCN → K₂[Co(SCN)₄] + 2KCl + 6H₂O

Safe­ty pre­cau­tions

Wear pro­tec­tive gloves and glass­es.

Warn­ing! Only un­der pro­fes­sion­al su­per­vi­sion.