Page 55 - Chemistry - XI

4. Iodides:

2I +H SO 2HI+SO 2
2
4
4
Conc.

2HI + O H O + I
2 2

5. Acetates: Violet

2CHCOO + H SO 2CHCOOH + SO 2
3 2 4 3 4
V inegar like smell

(B) CONFIRMATORY TESTS FOR ANIONS
For confi rmatory or wet test, a solution of the salt is prepared depending upon the solubility of the salt.

Either aqueous solution or sodium carbonate extract is used for this purpose.
1. Aqueous solution: Take little amount (about 0.5 g of salt) in a boiling tube. Add about 20 mL of
distilled water and boil the mixture for 2–3 minutes. Cool and fi lter. Collect the fi ltrate and is known
as aqueous solution.
2. Sodium carbonate extract: In case, the salt is not completely soluble in water, the sodium carbonate
extract is prepared.
Take about 1 g of the salt and add about 3 g of the solid sodium carbonate to it. Now add 20 mL of distilled

water to it. Boil the contents for 5–10 minutes. Cool and fi lter. The fi ltrate so obtained is called sodium
carbonate extract.

Theory of Sodium Carbonate or Soda extract
When an insoluble salt is heated with sodium carbonate in water, double decomposition reaction takes
place. So that, the anion present in the salt forms soluble sodium salt which goes into solution, but the
cation is converted into carbonate and gets precipitated which is removed by fi ltration. For example,

BaCl + NaCO BaCO + 2NaCl
2 2 3 3
Insoluble

S. No. Test Observation Inference

1. Test for carbonate CO
2
3
(a) Take a little salt in a test tube, add Salt insoluble in water. Insoluble CO

2
distilled water and shake. 3
(b) Treat the residue with dil. HCl. CO gas evolved which Insoluble CO

2
2
turns lime water milky. present 3
(c) To one part of the aqueous solution, White precipitate Soluble CO

2
add MgSO solution. 3
4 confi rmed
(d) Add phenolphthalein to another part Pink colour Soluble CO

2
of aqueous solution. confi rmed 3
(e) To another part of aqueous solution, CO gas evolved which Soluble 3
2
2 2
2
add dil. H SO . turns lime water milky. Soluble CO COCO 3 3
confi rmed rmed
2 4 confi
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