Nitric acid Manufacture by Ostwald's Process, Properties and uses.
. Nitric acid ( HNO3)
Manufacture of nitric acid is prepared by the catalytic oxidation of ammonia and can be done by following steps:
1). Ammonia is oxidized to nitric oxide by passing at 900° in the presence of pt catalyst.
4 NH3 + 5O2 Pt/800°c→6H2O + 4 NO ↑ +Heat
2). Nitric oxide thus Formed is cooled to about 50- 100°c and oxidized to nitrogen dioxide.
2 No + O2 → 2No2 ↑
3). Nitrogen dioxide is then converted into nitric acid by passing No2 gas in water in the presence of air.
4 No2 + O2 + 2H2o→4HNo3
Procedure
1). Oxidation of ammonia:
A mixture of dry air (free from carbondioxide and dust particles).and dry ammonia in the ration 8:1 by volume is first compressed and then passed into the catalytic chamber containing pt. gave as catalytiest at about 800°c . This results to the oxidation of ammonia into nitrogen molecular.
4 NH3 + 5O2 Pt/800°c→4 NO ↑ +6H2O + Heat
The reaction is exothermine and the heat eroked maintains the temperature of the catalytic chamber . The hot gases are then passed through a heat exchanger where they are mixed with air and passed into another cooling chamber called oxidizing chamber.
2). Oxiudation of Nitric Oxide
In this chamber nitric oxides combines with oxygen to from nitrogen dioxide at about 50°c -100°c.
2 NO +O2 ( 50-100°c)→ 2NO2 ↑
3). Absorption of Nitrogen Dioxide
The nitrogen dioxide together with the remaining air is passed through the absorption tower from the top of which warm water trickles. The nitrogen Dioxide and oxygen present in the air react with water to from nitric acid.
4 NO2 +2H2O+O2 →4 HNO3
The nitric acid Obtained at the bottom of the tower is concerntrated above 50% the acid on future distillation gives 68% nitric acid. The acid is Concerntrated nitric acid which is used in laboratories.
.Physical properties of Nitric acid (HNO3)
1. Nitric acid is a colourless liquid.
2. It is heavier than water.
3. It is soluble in water in all proportions.
4. commercial nitric acid is 68% conc. acid and it is a corst boiling mixture.
5. Its b.pt.is 85°c at ordinary atomsphere and solidified at -42°c.
. Chemical properties of Nitric Acid
1. Acidic nature
It is a very strong acid and is completely dissociated in equation solution.
HNO3 (aq) → H+ (aq) + NO3- (aq)
it turns blue litmus paper into red. where reacts with base it gives salt and water.
HNO3 + KOH → KNO3 + H2 O
HNO3 + Cao → Ca (NO3)2 + H2 O
2. Action with magnesium and mangance
3. Action with zinc
when zinc react with dilute nitric acid.
4 Zn →10 HNO3 → 4Zn (NO3)2 +N2O+5H2O
when Zinc react with conc. HNO3
Zn →4HNO3 → Zn (NO3)2 +2NO2 +2H2O
4. Action With iron
a.) iron reacts with very dil. HNO3 i.e about 6% and gets oxidized to ferrous nitrate and ammonium nitrate.
Fe + 2HNO3 → Fe (NO3)2 + 2 [H]
HNO3 + NH3 → NH4 No3
HNO3 + 8 [H] → NH3 + 3H2O
----------------------------------------------------
4Fe + 10 HNO3 → 4Fe (NO3)2 +NH4 No3 +3H2O
b.) With dil.HNO3
[ Fe + 2HNO3 → Fe (NO3)2 + 2H] ×4
2 HNO3 + 8 [H] → N2O+5H2O
----------------------------------------------------
4Fe +10HNO3 →4Fe (NO3)2 + N2O+5H2O
c.) With moderately conc. HNO3
Fe+ 3HNO3 →Fe (NO3)3 +3[H]
HNO3 + [H]→ No +H2O] × 3
----------------------------------------------------
Fe+ 6HNO3 →Fe (NO3)3 +3NO +3H2O (Ferric nitrall)
d.) With highy Conc.HNO3
When iron is treated with pure conc. HNO3 a layer of ferrosoferric oxide Fe3O4
gets deposited on the iron as impermeable coat iron does not react.
5. Action with copper
With cold and conc .HNO3
2 HNO3 → 2 No2 + H2O +[O]
Cu +[O] → Cuo
Cuo +2 HNO3 → Cu (NO3)2 + H2O
---------------------------------------------------
Cu +2 HNO3 → Cu (NO3)2 +2 H2O +2No2
With acid of moderate strength:
2 HNO3 → 2No + H2O +3[O]
Cu+[O] → Cuo] × 3
Cuo +2HNO3 → Cu (NO3)2 + H2O]× 3
---------------------------------------------
3Cu+8HNO3 →3 Cu (NO3)2 +4 H2O + 2NO
HNO3 Vapour When passed over strongly heated copper gives nitrogen.
5Cu +2HNO3 →5 CuO + H2O + N2 ↑
6. Action With iodine
I2 (OHNO3
7. Action with Phosphorous
P4 +2OHNO3
. Ring Test for Nitrate (NO3- )
Take 2-3 drops of HNO3 in a test tube dilute it. Take about 1ml of this dil.solution of HNO3 and about double volume of conc H2SO4 to it. Cool the mixture in cold water then add Freshly prepared FeSO4 solution slowly into the test tube of mixture maintained in inclined position. Brown ring is formed at the surface of the contact of the liquides.
Nitric acid oxidises FeSO4 in presence of H2SO4 into Fe2(SO4)3 and is itself reduced to NO. This no dissolves in excess of FeSO4 solution giving the brown coloured ring of FeSO4 NO,Nitrosoferrous sulphate.
6FeSO4 +3H2SO4 +2HNO3→ 3Fe2(SO4)3
+2NO +4H2O
FeSO4 + NO → FeSO4. NO nitrosoferrous sulphate (brown ring)
Uses of Nitric Acid (HNO3)
. It is very important Laboratory reagent.
. It is used for the Manufacture of explosive substances like TNT, dynamite picric acid etc. in combination with conc. H2SO4
. It is used in the manufacture of gold and silver.
. It is used as a solvent and a nitrating agent.
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