A student performing this lab experiment receives her Known solution and begins

Question

A student performing this lab experiment receives her Known solution and begins to conduct tests to identify the anions present. The acidification with nitric acid generates bubbles. The addition of aqueous barium nitrate to the remaining solution yields no precipitate. The addition of aqueous silver nitrate forms a whitish-yellow precipitate. This precipitate and solution is basified with 6M aqueous ammonia and centrifuged to separate this precipitate from its supernatant solution. The precipitate is tested with 16M aqueous ammonia and does not dissolve. The supernatant solution is acidified with nitric acid and a white precipitate forms. Which ions were present in the student’s unknown?

Explanation / Answer

Answer:

The Anion may be the halogen . Halogens can give the such type of the tests. The halogen anions are Cl-, Br- and I-.

According to the question:

1) AgNO3 --------- white yellow ppt

2) 6 M aqueous NH4OH solution ----- ppt does not dissolves.

These two can give the Iodine anion.

Hence the Anino is I-.

Note: In 6 M aqueous NH4OH solution the chloride and Bromide anions ppt can soluble.

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