Question

How would I test for the following ions?

Ammonium ion
Iron(II) ion
Zinc ion

Answer 1

How about these?

Explanation:

Testing for `"NH"_4^+`

The test

Add sodium hydroxide solution to the test solution and heat gently.

If ammonium ions are present, ammonia gas will be given off.

`"NH"_4^+("aq") + "OH"^"-"("aq") → "NH"_3"(g") + "H"_2"O"("l")`

Confirmation

Ammonia has a characteristic sharp, choking smell.

It makes damp red litmus paper turn blue.

It forms a white smoke of ammonium chloride on exposure to hydrogen chloride gas from a drop of concentrated hydrochloric acid on a glass stirring rod.

`"NH"_3("g") + "HCl(g)" → "NH"_4"Cl(s)"`

Testing for `"Fe"^(2+)`

The test

Add sodium hydroxide solution to the test solution.

You will get a dark green precipitate if `"Fe"^(2+)` is present.

`"Fe"^"2+"("aq") + 2"OH"^"-" → underbracecolor(green)("Fe(OH)"_2("s"))_color(green)("dark green precipitate.")`

Confirmation

Add a few drops of potassium hexacyanoferrate(III).

`"Fe"^(2+)` forms a deep blue precipitate.

`"3Fe"^(2+)("aq") + "2Fe(CN)"_6^(3+)("aq") → underbracecolor(blue)("Fe"_3["Fe(CN)"_6]_2("s"))_color(blue)("deep blue ppt.")`

Testing for `"Zn"^(2+)`

The test

Add a few drops of sodium hydroxide solution to the test solution.

You will get a white precipitate if `"Zn"^(2+)` is present.

`"Zn"^(2+)("aq") + "2OH"^"-"("aq") → underbrace("Zn(OH)"_2("s"))_color(black)("white ppt.")`

Confirmation

Add excess sodium hydroxide solution. The precipitate will dissolve.

`"Zn(OH)"_2("s") + "2OH"^"-"("aq") → "Zn(OH)"_4^"2-"("aq")`