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1.
Preparation
Mix the strong acid with the nitrite solution at low temperature to obtain the nitrous acid solution
.
NaNO 2 +H 2 SO 4 =HNO 2 +NaHSO 4
Passing the mixed gas of NO and NO 2 into ice water also generates an aqueous solution of nitrous acid
.
NO 2 +NO+H 2 O=2HNO 2
Nitrite can be obtained by decomposition or reduction of nitrate
.
2KNO 3 =2KNO 2 +O 2
Pb+KNO 3 =PbO+KNO 2
2.
Structure and properties
The trans structure of nitrous acid (HNO 2 ) is more stable (Figure 12-8), and there is a double bond between the N and the terminal O (a bond σ and a π bond)
.
NO 2 - and O .
FIG HN03 12-8 2 and NO 2 - Structure and π bond
HNO 2 is a weak acid (Ka Θ =7.
2×10 -4 ), and the potential diagram of related elements is as follows
It can be seen that nitrite is basically non-oxidizing, while nitrous acid is both oxidizing and reducing
.
Nitrous acid oxidizes I - fast.
It is generally believed that HNO 2 produces NO + in acidic solution, which is easy to approach I - and then undergo electron transfer, that is, redox products are obtained
Nitrous acid is unstable and decomposes quickly when the temperature is close to 0℃
.
KNO 2 and NaNO 2 are relatively stable and easily soluble in water; however, heavy metal salts have poor stability and are difficult to dissolve in water
.
For example, the pale yellow AgNO 2 is slightly soluble and decomposes when it is above 140°C
AgNO 2 =Ag+NO 2
NO 2 - complexing ability, many ions can be generated with a transition metal ion such as soluble of Na .
3 [of Co (NO 2 ) .
6 ] complex as a colorless, sparingly soluble K .
Related link: Nitrogen oxides