How would I test for the following ions?

Ammonium ion Iron(II) ion Zinc ion

Apr 24, 2016

Explanation:

Testing for ${\text{NH}}_{4}^{+}$

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.

$\text{NH"_3("g") + "HCl(g)" → "NH"_4"Cl(s)}$

Testing for ${\text{Fe}}^{2 +}$

The test

Add sodium hydroxide solution to the test solution.

You will get a dark green precipitate if ${\text{Fe}}^{2 +}$ 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).

${\text{Fe}}^{2 +}$ 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 ${\text{Zn}}^{2 +}$

The test

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

You will get a white precipitate if ${\text{Zn}}^{2 +}$ 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")