Carbon dioxide produced by action of dilute hydrochloric acid on potassium
hydrogen carbonate is moist whereas that produced by heating potassium hydrogen
carbonate is dry What would be the difference in the composition of carbon dioxide
in the two cases? State the associated law.
Answers
Answer: The difference is that there is water present in the hydrochloric acid and so water vapour is given off, thus dding a second gas to the mixture. This occurs even more often because the readtion is hot and thus more watwr evaporates from the acid.
Carbon dioxide produced by acid thus is impure as it is tainted water.
water is not present in calcium carbonate and thus when heated only carbon dioxide is produced and a pure product is formed. The by product is calcium hydroxide.
Carbon dioxide produced by both methods will have the same composition. The carbon dioxide obtained may have different purity but the chemical composition will remain the same. This is in accordance with the Law of Constant Proportions.
This law tells us that a compound will have the same chemical composition irrespective of the source from which we obtain it. This is because is composed by the same elements.
The exceptions to this law are:
- Compounds of isotopes
Isotopes have the same atomic number but differ in mass number.
- Non-stoichiometric compunds
These compounds do not have the fixed mass of an element present.