Question

“Aqua regia” is a combination of:
A. $HCl$ and ${{H}_{2}}S{{O}_{4}}$
B. $HCl$ and $HN{{O}_{3}}$
C. $HCl$ and $HBr$
D. $HCl$ and $HF$

Answer 1

Hint: Aqua regia is a very strong acid which is made by mixing a definite proportion of two different strong acids together. Those acids are strong in themselves but when they are mixed together in a certain proportion, they become much stronger and are used for various purposes.

Complete step by step solution:
-Aqua regia is made by the combination of two very strong acids in a certain proportion. Among all the options given, all acids are very strong acids except for HF which is due to the tendency of this compound to show hydrogen bonding.
-Strong acids are those acids which can dissociate themselves very easily to give the ${{H}^{+}}$ ions when mixed in a solution or a base. The acids give the characteristic neutralization reaction with the bases. In this reaction, they react with bases and give salt and water as the product.
-HF has the tendency to form hydrogen bonding with its own molecules and so it does not give its ${{H}^{+}}$ions very easily and so it is not a strong acid. So we can say that option D is wrong.
-${{H}_{2}}S{{O}_{4}}$ is sulphuric acid which is also known as king of acids owing to its very high acidic strength. So it does not need the support of any other acid to become stronger. So we can eliminate option A also.
-HBr is a stronger acid than HCl as the bromine atom is larger in size than the chlorine atom. The acidic strength depends on the size of the atom and increases with the increase in the size due to the tendency of the larger atom to eliminate the hydrogen ion from itself and also due to the increased stability of the larger ion.
-HCl is hydrochloric acid and $HN{{O}_{3}}$ is nitric acid. They are combined together to form aqua regia. They are strong acids but in comparison to other acids, they are not very strong and so are mixed together to form a stronger acid. Nitric acid and hydrochloric acid are combined in the ratio of 1:3 to form aqua regia.
-Aqua regia has a colour of yellow-orange and it exists as liquid. It can be used to dissolve a variety of metals in itself and so the name is kept. Many metals like gold, noble metals, silver, etc can get dissolved in this liquid.
-There are other names of aqua regia like royal water and nitrohydrochloric acid but the IUPAC name of aqua regia is nitric acid hydrochloride. Its chemical formula is $HN{{O}_{3}}+3HCl$

Therefore the correct option is B.

Note: No other combination of the mixture of the nitric acid and hydrochloric acid can give us aqua regia. They have to be mixed in the ratio of 1:3 only. Aqua regia is highly corrosive. It can dissolve many metals but not all the metals. It is also used in cleaning glassware and in etching.