Question

$NaCl\quad +\quad { H }_{ 2 }S{ O }_{ 4 }\quad \xrightarrow [ 420\quad K ]{ } \quad NaHS{ O }_{ 4 }\quad +\quad A$

What is A in the above reaction?
a) $HCl$
b) ${Na}_{2}S{O}_{4}$
c) $S{O}_{2}$
d) $S{O}_{3}$

Answer 1

Hint: The above reaction is a preparation method of a gas. This gas is colorless in appearance but produces white fumes when it comes in contact with atmospheric water vapour.

Complete-step- by- step answer:
The reaction given in the question very much depends upon the conditions in which it is taking place. The reaction will not take place if it was in aqueous conditions. But if we had sodium chloride in solid form and concentrated sulphuric acid then an acid/base reaction will occur. The sulphuric acid transfers a proton to a chloride ion and as a result it forms hydrogen chloride is gaseous form. Therefore, the product A in the reaction given is $HCl$ or hydrogen chloride gas.

The reaction taking place is given below:
${NaCl}_{(s)}\quad +\quad {{ H }_{ 2 }S{ O }_{ 4 }}_{(l)}\quad \xrightarrow [ 420\quad K ]{ } \quad {NaHS{ O }_{ 4 }}_{(s)}\quad +\quad {HCl}_{(g)}$

Steamy fumes of hydrogen chloride are observed.

Therefore, the correct option is A.

Note: Hydrogen chloride produced as a gas is bubbled off through a closed system ( like a round-bottomed flask with a hose and stopper) through distilled water to get hypochlorous acid (HClO) which will decompose into hydrochloric acid.