Nitric acid

Nitric acid

source : greener-industry.org.uk

1)  Oxidation of metal :

a) Reaction of Mg or Mn with very dilute HNO3 (6%):   Hydrogen is formed.

Mg + 2HNO3  ———-> Mg(NO3)2 +H2 

Mn + 2HNO3 ———-> Mn(NO3)2 +H2

b) Reaction of copper with  HNO3:

i) 3 Cu + 8HNO3 (dilute 20%)   ———> 3Cu(NO3)2 + 2NO+ 4H2O

ii) Cu + 4HNO3 (Concentrated)   ——–> Cu(NO3)2+ 2NO2 + 2H2O

c) Oxidation of silver with  HNO3 :

i) 3 Ag + 4HNO3 (dilute)  ——–> 3AgNO3(Lunar caustic) +NO + 2H2O

ii) Ag + 2HNO3 (concentrated) ——> AgNO3 +NO2 +H2O

d) Oxidation of lead:

i)  3Pb +  8HNO3 (dilute) ——>  3Pb(NO3)2 +  2NO +  4H2O

ii) Pb +  4HNO3 (dilute) ——>  Pb(NO3)2 +  2NO2 +  2H2O

e) Oxidation of Mercury :

i)  6 Hg + 8HNO3 (dilute) ——> 3Hg2(NO3)2 (mercurous nitrate) + 2NO + 4H2O

ii) Hg + 4HNO3 (concentrated) ——>Hg(NO3)2 (mercuric nitrate) +  2NO2 +  2H2O

f) Oxidation of Iron :

Iron does not react with highly conc. nitric acid (80%).It becomes passive due to formation of  a protective layer of ferric oxide. 

i)  4Fe + 1o HNO3 (dilute) ——> 4Fe(NO3)2 (ferrous nitrate) +  N2O +  5H2O

ii) Fe + 6HNO3 [ conc. (70%)] ——> Fe(NO3)3 (ferric nitrate) + 3NO2 + 3H2O

g) Oxidation of Zinc :

i) 4 Zn + 10 HNO3 (dilute) ——> 4 Zn(NO3)2 (zinc nitrate)+  N2O +  5H2O

ii) Zn +  4HNO3 (concentrated) ——> Zn(NO3)2 (zinc nitrate) +  2NO2 + 2H2O

h) Oxidation of Tin:

i)  4Sn + 10 HNO3 (dilute) ——> 4Sn(NO3)2 (stannous nitrate)+  NH4NO3 +  3H2O

ii) Sn + 4 HNO3 (concentrated) ——> H2SnO3 (meta stannic acid) + 4NO2 + H2O

2) Reaction of Al with Nitric acid:

Aluminium does not react with dilute or concentrated HNO3. It  is due to the formation of protective layer of Al2O3 at the surface of aluminium.

3) Reaction with protein :

Concentrated HNO3 burns the skin and produces yellow blisters to  make the skin yellow it is due to the formation of xanthoprotein.

xan

source : colinb-sciencebuzz.blogspot.com

Question: What is aqua regia ?

Solution :

The mixture of three part concentrated HCl and one  part concentrated HNO3 is called aqua regia. It is strong oxidizing agent . Most of the metals react with aqua regia . Nascent chlorine is liberated due to which aqua regia is very reactive  . Noble metals like Au , Pt dissolves in aqua regia.

3HCl + HNO3  ——–> NOCl(nitrosyl chloride) + 2Cl (nascent chloride)+ 2H2O

Reaction with Gold :

3HCl + HNO3 —–> NOCl + 2Cl + 2H2O ] x 3

Au + 3Cl ——> AuCl3 ] x 2

9 HCl + 3HNO3 ——-> 3 NOCl + 6Cl + 6H2O

2Au + 6Cl   ——-> 2AuCl3

Equation as a whole,

9 HCl + 3HNO3 + 2Au  ——-> 3 NOCl + 6H2O + 2AuCl3