Question

Which itself is used remove hardness of water and gas "c" is evolved. The gasic when pass through the lime water turn milky identify ABC.

Answer 1

Lime water is the common name for Ca(OH) 2. It is usually used for testing of carbon dioxide and sulphur dioxide as both the gases turns lime water milky .  

Carbon dioxide passed into limewater gives a milky solution. This is due to the insolublesuspension ofcalcium carbonateformed:

Ca(OH)2(aq)+ CO2(g)→ CaCO3(s)+ H2O(l)

If excess CO2is added, the following reaction takes place:

CaCO3(s)+ H2O(l)+ CO2(g)→Ca(HCO3)2(aq)

The milkiness disappears since calcium bicarbonate is water-soluble.

But the milkiness doesn't disappear instantly in case of sulphur dioxide rather it disappear on prolong passing of gas due to formation of calcium hydrogen sulphite.

Hence lime water is not considered effective in diffrentiating two gases.

Now in Order to effectively differentiate b/w two gases we should prefer following tests:

1) ODOUR TEST : CO2 is odourless gas where as SO2 is pungent smelling.

2) DICHROMATE PAPER TEST : SO2 turns potassium dichromate paper green where as CO2 does not undergo such change.  

Hope it helps

Answer 2

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