Question

(a) What happens when an acid reacts with a metal carbonate? Explain with the help of an example. Write a chemical equation of the reaction involved.
(b) What happens when carbon dioxide gas is passed through lime water.
(i) for a short time?
(ii) for a considerable time?
Write equations of the reactions involved.

Answer 1

In the above question, there are reactions that are involved, which are basically displacement reactions. The product formation can be understood once the way on how they’ll react is clear. In the second part, the clear answer can be obtained after writing the equations involved and obtaining the products in both cases ,i.e. for a short time as well as for a considerate amount of time.

Complete answer:
a) Whenever an acid reacts with a metal carbonate, there is a form of reaction that takes place which results in the formation of the products which include salt, carbon dioxide gas, and a water molecule(s).
The above stated can be chemically represented through the following general reaction:
$HX + MC{O_3} \to MX + C{O_2} + {H_2}O$
An example of the following type of reaction is when hydrochloric acid reacts with potassium chromate to form potassium chloride, carbon dioxide, and a water molecule.
$2HCl + {K_2}C{O_3} \to 2KCl + C{O_2} + {H_2}O$
b)
i) When carbon dioxide is passed through lime water, we observe that the lime water has turned milky due to the formation of calcium carbonate which appears as a white precipitate.
$Ca{(OH)_2} + C{O_2} \to CaC{O_3} + {H_2}O$

ii) When carbon dioxide is passed through lime water for a considerable amount of time, then the lime-water solution which has initially turned milky becomes clear due to the conversion of calcium carbonate into calcium bicarbonate. The reaction involved is:
$CaC{O_3} + C{O_2} + {H_2}O \to Ca{(HC{O_3})_2}$
This gives us a clear solution.

Note:
The reaction involved in all the above asked questions plays a very important role in the answer procedures. Unless and until the reactions are clear, there would be uncertainty in the answering question. Also, the color and the formation of precipitate and how it would appear also play a crucial role in the answer solving.