1.

The lassaigne's extract is boiled with dil.HNO_(3) before testing for halogens because

Answer»

Silver HALIDES are soluble in `HNO_(3)`
`Na_(2)S and NaCN` are DECOMPOSED by `HNO_(3)`
`Ag_(2)S` is soluble in `HNO_(3)`
AgCN is soluble in `HNO_(3)`

SOLUTION :`Na_(2)S and NaCN`, formed during fusion with metallic sodium must be rmoved before adding `AgNO_(3)`, otherwise black ppt. due to `Na_(2)S` or white precipitate due to AgCN will be formed and thus white precipitate of AGCL will not be identified easily.
`Na_(2)S+2AgNO_(3) to 2NaNO_(3)+underset("Black")(Ag_(2)S)darr`
`NaCN+AgNO_(3) to NaNO_(3)+underset("white")(AgCN)darr`
`NaCl+AgNO_(3) to NaNO_(3)+underset("white")(AgCl)darr`
`Na_(2)S+2HNO_(3) to 2NaNO_(3)+H_(2)Suarr`
`NaCN+HNO_(3) to NaNO_(3)+HCNuarr`


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