Potassium dichromate - sulphuric acid chloride ions

Potassium dichromate and sulphuric acid (chromyl chloride test) assemble a small, preferably all-glass, distillation apparatus as shown in Fig. 4.1. Place 10 ml 2m sodium hydroxide in the recipient test-tube. The sample which contains chloride must be in solid form. Mix the sample thoroughly with about three times as much powdered potassium dichromate, and place the mixture in the distillation flask. Add an equal volume of concentrated sulphuric acid and warm the mixture gently." Deep-red vapours of chromyl chloride, Cr02Cl2, are formed. When reacting with the sodium hydroxide in the recipient tube, chromyl chloride is converted to chromate ions, resulting in a yellow solution. The presence of chromate can be verified by appropriate reactions (cf. Section 4.33). 

---