Cations and Anions

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Confirmatory Tests for Cations & Anions
prepared by alex teoh / Update: 29 Dec 2004-2205 h / 1st pub: 7 Sep 2001 @ CHIJ-St Joseph’s Convent

Test for CATions
* All cations must be present in aqueous states before tests can be conducted..

CATion
ammonium zinc

Reaction with aqueous Sodium Hydroxide
NO ppt. Ammonia gas produced on warming. 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. [u] Ca2+ + 2OH-  Ca(OH)2 (white ppt) Insoluble in excess aq. NaOH. [w] White ppt. [p] Soluble in excess aq. NaOH to form a colorless solution. [q] Al3+ + 3OH-  Al(OH)3 (white ppt) Al(OH)3 + OH- [Al(OH)4]- (aq) White ppt. Soluble in excess aq. NaOH to form a colorless solution. Pb2+ + 2OH-  Pb(OH)2 (white ppt) Pb(OH)2 + 2OH- [Pb(OH)4]2- (aq) NO ppt.

Reaction with aqueous Ammonia

White ppt. Soluble in excess aqueous ammonia to form a colorless solution. Zn2+ + 2OH-  Zn(OH)2 (white ppt) Zn(OH)2 + 4NH3(aq) [Zn(NH3)4]2+ (aq) NO ppt. [x] or a very slight white ppt. White ppt. [s] Insoluble in excess aqueous ammonia. [t] Al3+ + 3OH-  Al(OH)3 (white ppt) White ppt. Insoluble in excess aqueous ammonia. Pb2+ + 2OH-  Pb(OH)2 (white 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) Dark green ppt. Insoluble in excess aqueous ammonia. Reddish-Brown ppt. Insoluble in excess aqueous ammonia.

calcium

aluminium

lead(II)

copper (II)

Blue ppt. [g] Insoluble in excess aq. NaOH. Cu2+ + 2OH-  Cu(OH)2 (blue ppt) Dark green ppt. [h] Insoluble in excess aq. NaOH. Fe2+ + 2OH-  Fe(OH)2 (dark green ppt) Reddish-Brown ppt. [k] Insoluble in excess aq. NaOH. Fe3+ + 3OH-  Fe(OH)3 (red brown ppt)

iron (II) iron(III)

NOTE: The observations for both lead(II) and aluminium ions are similar. To distinguish them, add aqueous potassium iodide KI to both solutions....
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