why nh4cl is not used in place of nacl to prepare hcl?

NH4Cl is not used in place of NaCl to prepare HCl because NH4Cl is an ammonium salt, whereas NaCl is a chloride salt. The reaction of NaCl with sulfuric acid (H2SO4) produces HCl gas.

The reaction between NaCl and H2SO4 can be represented as follows:
2NaCl + H2SO4 → 2HCl + Na2SO4

In this reaction, the chloride ion (Cl-) from NaCl is displaced by H+ from H2SO4, resulting in the formation of HCl gas. The sodium sulfate (Na2SO4) formed as a byproduct is soluble in water and does not interfere with the production of HCl.

On the other hand, when NH4Cl reacts with H2SO4, it forms ammonium sulfate (NH4)2SO4, not HCl. The reaction can be represented as:
2NH4Cl + H2SO4 → (NH4)2SO4 + 2HCl

In this case, the ammonium ion (NH4+) from NH4Cl is displaced by H+ from H2SO4, resulting in the formation of ammonium sulfate (NH4)2SO4, not HCl.

So, NH4Cl cannot be used to directly produce HCl gas. NaCl is preferred because it readily reacts with sulfuric acid to produce HCl gas, which can be collected and used for various purposes.