31/07/2025
NITROGEN AND IT'S COMPOUNDS
Introduction to oxides of nitrogen
Nirogen has a position in second period of group V in the modern periodic table. It has molecular formula N2. It has atomic number 7 and atomic weight 14.08 and its electronic configuration of 2,5.
Besides combining with hydrogen and forming NH3 , nitrogen combines with oxygen in different ratios and forms five different oxides.
The oxides of nitrogen and the details of the oxygen states of nitrogen and the N:O ratio can be presented in a tabular form as:
Name Formula Oxidation state of N Ratio of N:O
1) Nitrogen Oxide or
NO +2 1:1
nitrous oxide
2) Nitrogen dioxide NO2 +4 1:2
3) Nitrous oxide
N2O +1 2:1
(also called laughing gas)
All of these oxides of nitrogen are gases, excepting NO and N2O the other oxides are brownish gases. Except the oxides of NO and N2O all the other oxides are acidic. NO and N2O are neutral.
The other oxides are prepared in the laboratory using different methods characteristic to each oxide.
Example of Oxides of Nitrogen (nitric Oxide - NO)
Structure:
Laboratory Preparation: The oxide is prepared in the laboratory by treating the metallic copper with a moderately concentarted nitric acid (1:1) at room temperature.
The reaction is given as :
2Cu + 8 HNO3 ------> Cu(NO3)2 + 2NO + 4H2O
The gas is collected by downward displacement of water.The apparatus used is Wolfe's apparatus. The purification is done by absorbing the NO gas in frashly prepared ferrous sulphate solution. Ferrous sulphate absorbs all the NO gas and forms
Fe(H2O)5 NO and the solution becomes brown. On heating this solution pure Nitric Oxide is obatined.
Physical Properties: NO is not a combustible gas. At high temperature around 1000°C it decomposes into N2 and O2 .
2NO = N2 + O2 at high temperature
From the equation above we can see that once the decomposition starts 50% O2 gets evolved and this O2 supports combustion thus making the reaction more violent.
Chemical properties:
1) NO acts as an oxidising agent, oxidising SO2 in presence of water to give H2SO4: SO2 + 2NO + H2O → H2SO4 + N2O
2) NO acts as a reducing agent,
i) reducing an acidified solution of potassium permanganate (pink) to colorless manganous salt.
3KMnO4 + 6H2SO4 + 5NO2 → 3KHSO4 + 3MnSO4 + 2H2O + 5NO3
ii) It can also reduce aqueous solution of I2 to HI 3I2 + 2NO + 4H2O → 2HNO3 + 6HI
3) With halogens NO can form addition compounds as
2NO + Cl2 → 2NOCl (NOCl is nitrosyl chloride) It reacts in the same way with flourine and bromine.
4) With ferrous sulphate NO forms an addition compound as FeSO4 + 5H2O + NO = [Fe(H2O)5NO]SO4
penta aqua nitrosyl iron (II) sulphate
This is the famous brown ring test used to identify the nitrate radical or the NO radical.
Uses: NO is used to prepare nitric acid.
Nitrogen Dioxide - NO2
Structure:
Laboratory Preparation: In the laboratory NO2 is prepared by thermal decomposition of Pb(NO3)2. Thus
2Pb(NO3)2 → 2PbO + 4NO2 + O2
Care is taken to ensure the use of dried Pb(NO3)2 as hydrated nitrate salts on heating react violently and explode.
Physical Properties: NO2 is a poisonous gas, main source being the exhaust of automobiles.
1) At room temperature it is a deep brown gas.
2) It does not support combustion.
3) It is not combustible.
Chemical Properties:
1) With cold water NO2 reacts to give a mixture of HNO2 and HNO3 acid.
2NO2 + H2O → HNO2 + HNO3
2) With hot water the reaction is 3NO2 + H2O → 2HNO3 + NO
3) Being acidic it reacts with bases as
2NO2 + KOH → KNO3 + H2O + KNO2
4) It is also a strong oxidising agent.
H2S + NO2 → NO + H2S + S
5) With excess oxygen and water NO2 gives HNO3.
4NO2 + O2 + 2H2O → 4HNO3
6) It reacts with concentrated H2SO4 to give nitrosyl hydrogen sulphate 2NO2 + H2SO4 → SO2(OH)ONO + HNO3
Uses: NO2 is used as a fuel in rockets besides being used to prepare HNO3 .
Nitrous Oxide - N2O (laughing Gas)
Structure:
Laboratory Preparation: N2O can be prepared in the laboratory by heating NH4NO3 below 200°C to avoid explosion. Sometimes as a safety measure instead of directly using NH4NO3, a mixture of (NH4)2SO4 and NaNO3 are heated to give NH4NO3 which decomposes further to give N2O.
NH4NO3 → N2O + H2O (endothermic reaction)
Physical Properties:
1) N2O has a faint sweet smell and produces a tickling sensation on the neck when inhaled and makes people laugh hysterically. Excess of inhalation leads to unconsiousness.
2) Unlike other oxides of nitrogen, N2O supports combustion though it does not burn itself.
Chemical Properties:
1) At very high temperature N2O decomposes to N2 and O2 2N2O → 2N2 + O2
If a glowing piece of Mg, Cu, or P is introduced in such an environment, these pieces burn brightly due to the O2 produced from decomposition of N2O.
2) With Sodium and potassium N2O reacts to give the corresponding peroxides liberating N2 in the process.
2N2O + 2Na → Na2O + 2N2.
Na2O is sodium peroxide
Uses:
1) It is used as propellent gas.
2) Used in combination with oxygen in the ratio N2O : O2 = 1:10 as a mild anaesthetic.
