Potassium dichromate - K2Cr2O7
Potassium dichromate is a very common chemical in the laboratory. It has a beautiful bright orange/red color, it is a nice dry compound and its solutions are beautifully orange. Unfortunately it is believed to be a human carcinogen. On addition of a solution of KOH to a solution of potassium dichromate, the yellow potassium chromate is formed, which also is a dry non-hygroscopic compound, but also is a suspected human carcinogen.