99-AL-essay-2
Essay on Nitric(V) Acid
A.
Introduction
Pure nitric(V) acid is a colourless liquid while concentrated nitric(V) acid gives a colour of light brown
because of the dissolved nitrogen dioxide formed from the decomposition. Nitric(V) acid is usually
stored in a brown bottle to avoid photodecomposition.
The structure of nitric(V) acid:
H
O
O
N+
-
O
H
O
O
N+
-
O
Because of the delocalizaton of  electron, resonance occurs and two of the oxygen-nitrogen bonds are
partial double bonds. Their bond lengths are intermediate between single and double bond.
B.
Manufacture or Preparation of Nitric(V) Acid
1.
Industrial manufacture
Nitric(V) acid is manufactured industrially by the catalytic oxidation of ammonia.
The three stages of
Ostwald process are shown as follow:
Pt / high temp
 4NO(g) + 6H2O(g)
4NH3(g) + 5O2(g)   
 2NO2(g)
2NO(g) + O2(g) 
 4HNO3(aq)
4NO2(g) + O2(g) + 2H2O(l) 
2.
Laboratory preparation
Nitric(V) acid can also be prepared by heating nitrates(V) with concentrated sulphuric acid.
 NaHSO4(aq) + HNO3(aq)
NaNO3(aq) + H2SO4(l) 
C.
Chemical Properties of Nitric(V) acid
1.
Acidic properties
Dilute nitric(V) acid acts as a strong acid.
 H+(aq) + NO3-(aq)
HNO3(aq) 
It gives neutralization reaction with alkalis, hydrocarbonates, carbonates and metal.
Example
 NaNO3(aq) + H2O(l)
NaOH(aq) + HNO3(aq) 
 2NaNO3(aq) + H2O(l) +CO2(g)
Na2CO3(aq) + 2HNO3(aq) 
2.
Oxidizing properties
Nitric(V) acid is a strong oxidizing agent.
reduced, nitrogen monoxide is formed.
formed.
If dilute or moderately concentrated nitric(V) acid is
If concentrated nitric(V) acid is reduced, nitrogen dioxide is
99-AL-essay-2
a)
Reaction with metals
Reaction with copper is used as an example. The oxidation state of copper changes from 0 to +2.
The colour of the solution changes from colourless to blue and brown gas is given.
 Cu(NO3)2(aq) + 2NO2(g) + 2H2O(l)
For concentrated HNO3: Cu(s) + 4HNO3(aq) 
For diluted HNO3:
 3Cu(NO3)2(aq) + 2NO(g) + 4H2O(l)
3Cu(s) + 8HNO3(aq) 
For very dilute HNO3, N2O is formed.
 4Zn(NO3)2(aq) + 5H2O(l) + N2O(g)
4Zn(s) + 10HNO3(aq) 
b)
Reaction with non-metals
Sulphur, phosphous and carbon can be oxidized by HNO3 to their highest oxidation state.
 H2SO4(aq) + 6NO2(g) + 2H2O(l)
S(s) + 6HNO3(aq) 
 H3PO4(aq) + 5NO2(g) + H2O(l)
P(s) + 5HNO3(aq) 
 CO2(g) + 4NO2(g) + 2H2O(l)
C(s) + 4HNO3(aq) 
c)
Others reactions
 3Fe3+(aq) + NO(g) + 2H2O(l)
3Fe2+(aq) + 4H+(aq) + NO3-(aq) 
 4H2O(l) + 2NO(g) + 3S(s)
3H2S(g) + 2HNO3(aq) 
It can also be used in nitration of benzene.
NO2
conc. HNO3
conc. H2SO4
D.
Uses of nitric(V) acid
-
It can be used to manufacture nitrogenous fertilizer such as NaNO3 and NH4NO3.
-
It can be used to manufacture explosive such as KNO3.
-
Manufacture of azo dyes also needs nitric(V) acid.
-
It is used for the treatment of metals.
For example, nitric(V) acid can produce a layer of oxide
on iron and this makes the metal passive.
E.
Test for nitric(V) acid
Concentrated HNO3 reacts with copper to give brown gas of NO2.
 Cu(NO3)2(aq) + 2NO2(g) + 2H2O(l)
Cu(s) + 4HNO3(aq) 