Question

Which of the following acts as pickling agent?
A. \[HN{O_3}\]
B. \[HCl\]
C. \[{H_2}S{O_4}\]
D. \[HN{O_2}\]

Answer 1

Hint: Pickling is a process to remove the impurities like, strain, rust, from ferrous metals by using pickle liquor and copper solution is used as pickle liquor.

Complete step by step answer:
Pickling is performed by dipping the metal into the pickle liquor. This pickle liquor contains strong acids like \[{H_2}S{O_4}\], \[HCl\] etc. in this process when a piece of metal is submerged in to the acid solution the impurities like oxide, rust, scale, strain get eaten by the acid solution.
So, among the options \[{H_2}S{O_4}\], and \[HCl\] act as a pickling agent.

So, the correct options are, C and B.

Additional information:
There are so many processes to purify metals, among them some efficient processes are,
Electrolytic refining: In this process the impure metal and pure metal are taken as anode and cathode respectively. A salt of that particular metal is taken as electrolyte. When electricity is passed the impure metals get oxidized and converted into ions. On the other hand, metal ions from the solution get reduced at cathode. By this way metal get purified and the impurities get separated and get collected under anode electrode.
Zone refining: when the solubility of the impurities is greater in molten state than in solid state of the metal, this process is used. In this process an impure metal rod is heated by a moving heater from one end to another. When one end of the metal melts the impurities get soluble and concentrated into that particular melted area, and when the heater moves forward it leaves pure solidified metal behind.
Van Arkel method: this method is also called Vapour Phase refining. In this process a volatile impure metal is heated. As a result, the metal gets vaporised and impurities left behind are solid.
The Mond process: in this process the impure metal reacts with CO and forms gaseous metal carbonyl. The impurities are left unreacted.

Note: Pickling process has some disadvantages as well. Spent pickle liquor is a hazardous waste generated by this process. It also has some limitations as acid cleaning is difficult to handle due to corrosiveness, due to which it cannot be applied to all steels.