Page 60 - Chemistry - XI

Chemical Reactions Involved in Confirmatory Tests for Anions

1. Test for CO 2−
3
(a) Dilute HCl test:

2
CO +2HCl 2Cl +H O+CO

3 2 2

CaOH+CO CaCO +H O
2
3
2
2

Limee water White ppt.

CaCO+CO +H O CaHCO
3 2 2 3 2
Soluble

(b) MgSO test:
4
CO +MgSO MgCO +SO 2
2
3 4 3 4
2−
2. Test for SO
3
(a) Barium chloride test:
2
SO+ BaCl BaSO +2Cl
3 2 3
White ppt.

BaSO +2HCl BaCl +H SO
3 2 2 3
S
olublee

(b) Potassium permanganate test:
2
2
2KMnO+5SO+3H SO 2MnSO+ KSO+5SO+3H O
4 3 2 4 4 2 4 4 2
Colourless
(c) Potassium dichromate test:

KCrO +3SO +4HSO 4Cr SO +3SO +K SO +4HO
2
2
2 2 7 3 2 4 2 4 3 4 2 4 2
3. Test for S 2-
(a) Nitroprusside test:

Fe CN NO Na Fe CN NOS
Na S + Na 4
2 2 5 5
V iolet colouration
(b) Lead acetate test:

S+ CH COOPb Pbs +2CH COO
2
3 2 3

Black ppt.
(c) Cadmium carbonate test:
S+CdCO CdS+CO 2
2
3
3
Yellow ppt.
−
4. Test for NO
2
(a) FeSO test:
4

NO +CHCOOH CH COO+ HNO

NO
2 3 3 2
4HNO → HNO + HNO +H O+ 2NO
4HNO
2 2 3 2
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