What is the active ingredient in #"aqua regia"#?

1 Answer
anor277
Dec 4, 2017

The active ingredient is #"nitrosyl chloride"#, #NOCl#...

Explanation:

Nitric acid is reduced to #NO^+#

#HNO_3 +3H + 2e^(-)rarr NO^+ +2H_2O# #(i)#

Chloride anion is oxidized to chlorine....

#Cl^(-) rarr 1/2Cl_2 + e^(-)# #(ii)#

We take #(i)+2xx(ii)#

#HNO_3 +3H^+ +2Cl^(-) rarr NO^+ +2H_2O+ Cl_2 #

And we add #1xxCl^-# to EACH SIDE....

#HNO_3 +3HCl rarr NOCl +2H_2O+ Cl_2 #

And this gives the formal 3:1 stoichiometry.....I have always thought it works better when you add EQUAL volumes of conc. acids....(of course when you prepare it you are using #36%# #HCl# and #70%# #"nitric"#).

Nitrosyl chloride is a potent oxidant...and is source of #NO#, the which is further oxidized to #NO_2#...

#2NOCl(g) rarr2NO(g) + Cl_2(g)#

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