Explain chromyl chloride test for chlorides.

Explanation

When potassium dichromate is heated with concentrated HCl or with a metal chloride and concentrated `H_2SO_4` , chromyl chloride is obtained as reddish brown vapours. It helps in the detection of chlorides. The reaction is as follows:
`K_2Cr_2O_7 + 4KCl + 6H_2SO_4 to underset("Reddish vapours of chromyl chloride. ")(2CrO_2Cl_2 + 6KHSO_4 + 3H_2O`
Now, vapours of chromyl chloride are passed through NaOH, followed by acetic acid and lead acetate. Yellow precipitates of lead chromate are formed. It confirms the presence of chlorides.
`CrO_2 Cl_2 + 2NaOH to Na_2CrO_4 + 2HCl`
`Na_2CrO_4 + Pb (CH_3COO)_2 overset("acid")(to) underset("yellow ppt.")(PbCrO_4 ) + 2CH_3COONa`