when bubbles are formed during a chemical reaction how would we know that its a release of that particular gas

Asked by vikramsingh | 16th Apr, 2013, 09:00: PM

Expert Answer:

It depends on the kind of bubbles!
When a liquid boils, it forms bubbles - but in this case it's only a physical change in the state of aggregation (from liquid to gaseous).
Another possibility in a physical cause of bubbles could be "out-gassing" of a physically solved gas in a liquid e.g. when you heat water of a lake, there forms tiny bubbles of oxygen because solubility decreases with rising temperature.
And now the case of a chemical reaction:
There you have a gas forming because of a chemical reaction - for example when you take the reaction between a (reactive) metal and an acid:
Mg + 2 HCl --> MgCl2 + H2(g)
In this case there is hydrogen (as a gas) which forms bubbles.
In a bottle of gassed mineral water you have both; physical and also chemical evolution of bubbles. Most of the carbon dioxide is solved physically in the water, but some is also bound chemically as carbonic acid H2CO3 which is not that stable and on shaking/heating splits up into CO2 and water:
H2O + CO2 <---> H2CO3
So forming of bubbles is not always an indication of a chemical reaction, but besides boiling of liquids a lot of gas evolutions are caused by a reaction!

Answered by  | 17th Apr, 2013, 11:02: AM

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