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Confirmatory Tests for Cations& Anionsp re pa re d b y a l ex te oh / U pd a te : 2 9 D e c 2 00 4- 22 05 h / 1 s t p u b: 7 S ep 2 00 1 @ C H IJ -S t J os ep h s C o n v e nt

Test forCATions

* All cations must be present in aqueous states before tests can be conducted..CATion

Reaction w i th aqueousSodium H y droxide

Reacti on w i thaqueous Ammonia

ammoniumNO ppt. Ammonia gas producedon warming.

NO ppt.

zinc

White ppt. [y] Soluble in excess aq.NaOH to form a colorless solution. [z]Zn2+ + 2OH- Zn(OH)2 (white ppt)Zn(OH)2 + 2OH

-[Zn(OH)4]

2- (aq)

White ppt. Soluble in excess aqueousammonia to form a colorless solution.Zn2+ + 2OH- Zn(OH)2 (white ppt)Zn(OH)2 + 4NH3(aq) [Zn(NH3)4]

2+ (aq)

calciumWhite ppt. [u]Ca2+ + 2OH- Ca(OH)2 (white ppt)Insoluble in excess aq. NaOH. [w]

NO ppt. [x] or a veryslight white ppt.

aluminium

White ppt. [p] Soluble in excessaq. NaOH to form a colorless solution. [q]Al3+ + 3OH- Al(OH)3 (white ppt)Al(OH)3 + OH

-[Al(OH)4]

- (aq)

White ppt. [s] Insolublein excess aqueous ammonia. [t]Al3+ + 3OH- Al(OH)3 (white ppt)

lead(II)

White ppt. Soluble in excessaq. NaOH to form a colorless solution.Pb2+ + 2OH- Pb(OH)2 (white ppt)Pb(OH)2 + 2OH

-[Pb(OH)4]

2- (aq)

White ppt. Insolublein excess aqueous ammonia.Pb2+ + 2OH- Pb(OH)2 (white ppt)

copper (II)

Blue ppt. [g]

Insoluble in excess aq. NaOH.Cu2+ + 2OH- Cu(OH)2 (blue ppt)

Blue ppt.[i]Soluble in excess aqueous ammonia to

form a dark blue solution. [m]Cu2+ + 2OH- Cu(OH)2 (blue ppt)Cu(OH)2 + 4NH3(aq) [Cu(NH3)4]

2+(aq )

iron (II)Dark green ppt. [h]Insoluble in excess aq. NaOH.Fe2+ + 2OH- Fe(OH)2 (dark green ppt)

Dark green ppt. Insoluble inexcess aqueous ammonia.

iron(III)Reddish-Brown ppt. [k]Insoluble in excess aq. NaOH.Fe3+ + 3OH- Fe(OH)3 (red brown ppt)

Reddish-Brown ppt. Insolublein excess aqueous ammonia.

NOTE: The observations for both lead(II) and aluminium ions are similar. To distinguish them, addaqueous potassium iodide KI to both solutions. Only lead(II) ions will give a yellow ppt.

p q s t

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u w x y z

h k g i m

Test forANionsChloride, iodide, nitrate and sulfate ions must be present in aqueous states before testscan be conducted.

Anion Test Observation ( if test is positive )

carbonate Add dilute hydrochloric ornitric acid.

Effervescence; bubbles of carbon dioxideproduced. A white ppt is formed when carbdioxide is bubbled through limewater.Ca(OH)2 + CO2 CaCO3 (white ppt) + H2O

chloride(in aqueous solution )

Add aqueous silvernitrate. Then acidify withdilute nitric acid.

A white ppt.(pic a) is formed. White pptremains on the addition of dilute nitric acid.

Ag+ + Cl- AgCl (white ppt)

iodide(in aqueous solution )

Add aqueous lead(II)

nitrate. Then acidify withdilute nitric acid.

Yellow ppt. (pic b) is produced. Yellow ppt

remains on the addition of dilute nitric acid.Pb2+ + 2I- PbI2 (white ppt) yellow ppt

nitrate(in aqueous solution )

Add aqueous sodiumhydroxide and thenaluminium foil.Warm gently.

Moist red litmus paper turns blue(Ammonia gas produced)

3NO3- + 8Al + 5OH- + 18H2O

3NH3 + 8Al(OH)4-

sulphate(in aqueous solution )

Add aqueous bariumnitrate (or aqueousbarium chloride). Then,acidify with dilute nitric ordilute hydrochloric acidrespectively.

A white ppt. (pic c) is formed. White pptremains on the addition of dilute hydrochloracid (or dilute nitric acid )

Ba2+ + SO42-

BaSO4 (white ppt)

a b c

Last Update: alexteoh - 2008June22 / Sunday / 1800h-1930h