How would I test for the following ions?

Ammonium ion
Iron(II) ion
Zinc ion

1 Answer
Apr 24, 2016

Answer:

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")#