Platinum metal is very reactive

Pure palladium is a silvery, shiny metal that can turn yellowish in the air through a slow reaction with the oxygen in the air. It is harder than platinum, but it can be forged well and rolled into thin foils like gold. One cubic centimeter of palladium sponge can absorb almost one liter of hydrogen at room temperature. One cubic centimeter of finely divided, black palladium powder in an aqueous suspension absorbs up to twelve liters of hydrogen. The resulting metal hydrides are suitable for the production of hydrogen storage systems for hydrogen cars. When heated, the hydrogen escapes; it is then in a particularly reactive form. Heated palladium sheets are permeable to hydrogen and are used to purify hydrogen.



Osmium, palladium and platinum


 
The palladium (in the middle) appears more yellow compared to the platinum (right).
 
 

Of all platinum metals, palladium is the least noble and most reactive metal. Hydrochloric acid and sulfuric acid do not attack the metal, but hot, concentrated nitric acid does. Yellow-brown palladium nitrate is formed in the process. When heated in air or with oxygen, black palladium (II) oxide is formed:

  
2 Pd + O2  2 PdO ΔHR. = −171 kJ / mol
  

This reaction can also take place slowly in air. Palladium only reacts with chlorine at 500 ° C to form palladium (II) chloride:

  
Pd + Cl2  PdCl2        ΔHR. = −172 kJ / mol
  

A corresponding reaction also takes place with sulfur, phosphorus, selenium, arsenic and other non-metals with the formation of the corresponding salts. If palladium is alloyed with silver, tarnishing of the silver is prevented by sulphide-containing air.



Palladium crystals



This crystal aggregate was artificially grown.