2
          
          
            NaNO
            
              2
            
            
              
            
          
          ⟶
          
            Na
            
              2
            
            
              
            
          
          O
          +
          NO
          +
          
            NO
            
              2
            
            
              
            
          
        
      
    
    {\displaystyle {\ce {2 NaNO2 -> Na2O + NO + NO2}}}
  Sodium nitrite can also be used in the production of nitrous acid:

  
    
      
        
          2
          
          
            NaNO
            
              2
            
            
              
            
          
          +
          
            H
            
              2
            
            
              
            
          
          
            SO
            
              4
            
            
              
            
          
          ⟶
          2
          
          
            HNO
            
              2
            
            
              
            
          
          +
          
            Na
            
              2
            
            
              
            
          
          
            SO
            
              4
            
            
              
            
          
        
      
    
    {\displaystyle {\ce {2NaNO2 + H2SO4 ->2 HNO2 + Na2SO4}}}
  The nitrous acid then, under normal conditions, decomposes:

  
    
      
        
          2
          
          
            HNO
            
              2
            
            
              
            
          
          ⟶
          
            NO
            
              2
            
            
              
            
          
          +
          NO
          +
          
            H
            
              2
            
            
              
            
          
          O
        
      
    
    {\displaystyle {\ce {2 HNO2 -> NO2 + NO + H2O}}}
  The resulting nitrogen dioxide hydrolyzes to a mixture of nitric and nitrous acids:

  
    
      
        
          2
          
          
            NO
            
              2
            
            
              
            
          
          +
          
            H
            
              2
            
            
              
            
          
          O
          ⟶
          
            HNO
            
              3
            
            
              
            
          
          +
          
            HNO
            
              2
            
            
              
            
          
        
      
    
    {\displaystyle {\ce {2 NO2 + H2O -> HNO3 + HNO2}}}

Isotope labelling 15N
In organic synthesis isotope enriched sodium nitrite-15N can be used instead of normal sodium nitrite as their reactivity is nearly identical in most reactions.
Urea, also known as carbamide-containing cream, is used as a medication and applied to the skin to treat dryness and itching such as may occur in psoriasis, dermatitis, or ichthyosis. It may also be used to soften nails.In adults side  effects are generally few. It may occasionally cause skin irritation. Urea works in part by loosening dried skin. Preparations generally contain 5 to 50% urea.Urea containing creams have been used since the 1940s. It is on the World Health Organizations List of Essential Medicines. It is available over the counter. Medical uses
Urea cream is indicated for debridement and promotion of normal healing of skin areas with hyperkeratosis, particularly where healing is inhibited by local skin infection, skin necrosis, fibrinous or itching debris or eschar. Specific condition with hyperkeratosis where urea cream is useful include:

Dry skin and rough skin
Dermatitis
Psoriasis
Ichthyosis
Eczema
Keratosis
Keratoderma
Corns
Calluses
Damaged, ingrown and devitalized nails

Side effects
Common side effects of urea cream are:

Mild skin irritation
Temporary burning sensation
Stinging sensation
ItchingIn severe cases, there can be an allergic reaction with symptoms such as skin rash, urticaria, difficulty breathing and swelling of the mouth, face, lips, or tongue. Mechanism of action
Urea in low doses is a humectant while at high doses (above 20%) it causes breakdown of protein in the skin.Urea dissolves the intercellular matrix of the cells of the stratum corneum, promoting desquamation of scaly skin, eventually resulting in softening of hyperkeratotic areas. In nails, urea causes softening and eventually debridement of the nail plate. References
External links
"Urea". Drug Information Portal. U.S. National Library of Medicine.