Question

A solution reacts with crushed egg-shells to give a gas that turns lime-water milky. The solution contains:
\[
  A.{\text{ }}NaCl \\
  B.{\text{ }}HCl \\
  C.{\text{ }}LiCl \\
  D.{\text{ }}KCl \\
 \]

Answer 1

Hint: In order to solve the given problem first we will understand the chemical composition of egg shells further we will understand the chemical reaction of the egg shell with the solution given in the option which gives out some gases. Further we will try to find out the gas evolved in the reaction of the egg shell and the acid on the basis of the test of different gases with the lime-water and further on the basis of the gas evolved we will try to find out the acid involved in the reaction.

Complete answer:
We know that the egg-shells are generally composed of calcium carbonate material. Further the chemical formula for calcium carbonate is $CaC{O_3}$ .
Let us look for the gas which turns the lime water milky.

Chemical composition of lime water is calcium hydroxide and its chemical formula is $Ca{\left( {OH} \right)_2}$
We know that whenever carbon dioxide $C{O_2}$ reacts with calcium hydroxide it produces calcium carbonate and water.
The reaction is given as:

$Ca{\left( {OH} \right)_2} + C{O_2} \to CaC{O_3} + {H_2}O$

In this reaction the product calcium carbonate is white in colour and is responsible for lime water to turn milky.
So from the above reaction we can understand that the gas produced in the required reaction must be carbon dioxide.
Now let us look for the reaction of calcium carbonate which produces carbon dioxide.
As we know that whenever calcium carbonate reacts with acid the product also contains carbon dioxide.
So, the solution must be hydrochloric acid or $HCl$ .
Let us see the reaction of calcium carbonate or egg shells with hydrochloric acid.

$CaC{O_3} + 2HCl \to CaC{l_2} + C{O_2} + {H_2}O$

From the above reaction it is clear that the solution present in the reaction is Hydrochloric acid. In order to get the according result and product.
Hence, the solution contains $HCl$ .
So, the correct answer is option B.



Note: In order to solve such problems students must remember the test for different chemical compounds one of which is mentioned in the solution. Students must remember the chemical composition of some practical materials. Before reaching to some conclusion students must remember to check for all the parts of the problem.