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Nitrous Acid

Nitrous Acid

source :en.academic.ru

Nitrous Acid [HNO2]

Method of preparation :

a) By the reaction of NaNO2 with cold and dilute H2SO: nitrous  acid is formed.

2 NaNO2 (Sodium nitrite) + H2SO4 (dilute)  ——-> 2HNO2 (Nitrous acid) +Na2SO4

b) By the reaction of Barium nitrite [ Ba(NO2)2] with cold and dilute H2SO4  :  At 00c nitrous  acid is formed.

Ba(NO2)2 +H2SO4 ——–> 2HNO2 +BaSO4

Properties :

1) Acidic nature :

It is a weak  monobasic acid. It forms salt with base.

HNO2 + NaOH ——-> NaNO2 (sodium nitrite) +H2O

2) Oxidizing properties :

a) SO2 is oxidized into H2SO:

2HNO2 ——-> H2O + 2NO + O

SO2 + O + H2O —–>H2SO4

Equation as a whole,

2HNO2 + SO2  ——> 2NO + H2SO4

b) It oxidizes H2S into sulphur :

2HNO2 ——-> H2O + 2NO + O

H2S+ O ——> H2O + S

Equation as a whole,

2HNO2 +H2S ——> 2H2O + 2NO + S

c) It oxidizes Na2SO3 into Na2SO:

2HNO2 ——-> H2O + 2NO + O

Na2SO3 + O ——> Na2SO4

Equation as a whole,

2HNO2 +Na2SO3 —-> H2O + 2NO + Na2SO4

d) It oxidizes acidic KI into K2SO:

2HNO2   —-> H2O + 2NO + O

2KI +H2SO4 +O —–>K2SO4 +I2 +H2O

Equation as a whole,

2HNO2 + 2KI +  H2SO4 ——> 2H2O + 2NO +K2SO4 +I2

e) It oxidizes SnCl2  into SnCl4 :

2HNO2 ——> H2O + 2NO + O

SnCl2 + 2HCl +O ——-> SnCl+ H2O

Equation as a whole,

2HNO2 + SnCl2 + 2HCl —–>  SnCl4  + 2NO +  2H2O

3) Reducing properties :

HNO2 itself is oxidized into HNO3 therefore HNO2 acts as reducing agent.

a) Cl2 is reduced to HCl :

Cl2+ H2O —–> 2HCl + [O]

HNO2 + [O]  ——> HNO3

Equation as a whole,

Cl2 + H2O + HNO2 ——> HNO3 + 2HCl

b) H2O2 is reduced into H2O :

H2O2 ——> H2O + [O]

HNO2 + [O]  —–> HNO3

Equation as a whole,

H2O2 + HNO2 —–>H2O + HNO3

c) Acidic KMnO4 is reduced to MnSO4 and pink color of KMnO4 disappears :

2KMnO4 + 3H2SO4 ——->K2SO4 +   2MnSO4 + 3H2O + 5[O]

5HNO2 + 5[O]    ————-> 5HNO3

Equation as a whole,

2KMnO4 +3H2SO4 + 5HNO2 ——-> K2SO4 + 2MnSO4 + 3H2O + 5HNO3

d) Acidic K2Cr2O7 is reduced to Cr2(SO4):

K2Cr2O7 + 4H2SO4 ——->K2SO4 + Cr2(SO4)3 + 4H2O + 3[O]

3HNO2 + 3[O] —–> 3HNO3

Equation as a whole,

K2Cr2O7 + 4H2SO4 + 3HNO2 ———-> K2SO4 + Cr2(SO4)3 +4H2O +3HNO3

HNO2 acts as oxidizing as well as reducing agent:

4) Reaction with Urea :

Nitrogen , carbon dioxide & water is formed.

NH2CONH2 + 2HNO2 ——> 2N2 + CO2 + 3H2O

5) Reaction with ethylamine : Ethyl alcohol is formed.

C2H5NH2 + HNO2 ——> C2H5OH + N2 + H2O

Question: What is the effect of heat on NH4NO2 and NH4NO?

Solution :

NH4NO3( ammonium nitrate) —–> N2O (Nitrous oxide) + 2H2O

NH4NO2 (ammonium nitrite) ——>  N2 (Nitrogen) + H2O

Test : 

1) It decolourises the pink colour of acidic KMnO4

2) It gives  green  colour  with  acidic K2Cr2O7.

3) It makes Starch iodide solution violet.

 

Saroj Bhatia: Dr. Saroj Bhatia is an Ph.D in chemistry who has been teaching chemistry for over a decade. Currently she is a respected principal of a renowned college in her hometown. She took this medium for online users. Her proudest achievement is helping people learn chemistry.
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