Question

In one of the industrial processes used for manufacture of sodium hydroxide, a gas ‘X’ is formed as a by-product. The gas ‘X’ reacts with lime water to give a compound ‘Y’ which is used as a bleaching agent in the chemical industry. Identify ‘X’ and ‘Y’.
A.) X is chlorine; Y is baking soda
B.) X is chlorine; Y is bleaching powder
C.) X is hydrogen; Y is potash
D.) X is hydrogen; Y is plaster of Paris

Answer 1

Hint: Whenever common salt and water react together then sodium hydroxide is produced along with hydrogen and chlorine gas. This process is called the chlor-alkali process.

Complete step-by-step answer:
We have been given in the question that in the industrial process for the manufacture of sodium hydroxide, a gas X is formed as a by-product.
And the gas ‘X’ reacts with lime water to give a compound ‘Y’, which is used as a bleaching agent.
So, we know that common salt, i.e., $NaCl$ is used for the manufacture of sodium hydroxide, i.e., $NaOH$ and this process is called the chloro-alkali process.
The chemical equation of this process is-
$2NaCl(aq) + 2{H_2}O(l)\xrightarrow{{}}2NaOH(aq) + C{l_2}(g) + {H_2}(g)$
So, as mentioned in the question that in the manufacture of the sodium hydroxide, a gas ‘X’ is formed as a by- product.
So, if we see the above chemical reaction, chlorine and hydrogen gases are formed as the by-product.
It is also given that the gas X reacts with lime water, so among chlorine and hydrogen, chlorine reacts with lime water, so the gas ‘X’ is chlorine.
Therefore, X is chlorine gas.
 Now, also given that X reacts with lime water to get compound Y.
i.e., X + lime water gives a Y compound.
Lime water has chemical formula $Ca{(OH)_2}$ and we already know X is chlorine.
So, let us write chemical reaction equation for this-
$Ca{(OH)_2} + C{l_2}\xrightarrow{{}}CaOC{l_2} + {H_2}O$
Now, we can see that when Chlorine reacts with lime water it gives, $CaOC{l_2},{H_2}O$ .
Now, as given in the question that compound Y is used as a bleaching agent, hence compound Y is Calcium oxychloride, i.e., $CaOC{l_2}$ which is commonly known as bleaching powder and used as bleaching agent in chemical industries.
Therefore, compound Y is bleaching powder, i.e., $CaOC{l_2}$ .
Hence, the answer is option B.

Note – Whenever such types of questions appear, a very important thing to keep in mind while solving is that, do write the chemical equations involved, so that you will not make any mistake while solving. As mentioned in the solution, first we have written an equation for the manufacture of sodium hydroxide and then found out X and then writing a chemical equation for the reaction of X with lime water, we got the value of Y.