ArticleManagerTypical oxidizing acid – nitric acid
Name of the drug
nitric acid
English name
Nitric acid
molecular weight
63.01
EINECS login number
231-714-2
boiling point
122℃
density
1.42g/cm³ (mass fraction 69.2%)
flash point
Pointless
Hazard symbols
O (oxidant), C (corrosive)
Dangerous goods transport number
81002 UN
Type of regulation
Corrosive products, easy to make explosions
alias
Nitrate water, ammonia nitrogen water
chemical formula
HNO₃ (solute formula)
CAS registration number
7697-37-2
melting point
-42℃
water solubility
Soluble in water
appearance
Pure nitric acid is a colorless liquid
apply
For the production of nitrogen fertilizer, aqua regia, nitrate, nitroglycerin
Hazard description
Contact with nitric acid vapor is very dangerous
attribute
Chemical reagents, acid corrosive products
stability
Unstable, it will decompose when exposed to light or heat
1. Physical properties
Nitric acid is a colorless, volatile liquid that has
Irritation
Odor, miscible with water in any proportion.
2. Chemical properties
(1) Instability:
(1) Reaction: 4HNO3△2H2O+4NO2↑+O2↑.
(2) The reason why commercially available concentrated nitric acid is yellow is that NO2 generated by the decomposition of nitric acid is dissolved in nitric acid.
(3) Nitric acid is stored
brown
Reagent bottle, placed in a cold dark place, can not use rubber stopper.
(2) Strong oxidation:
Both concentrated and dilute nitric acid has strong oxidation, and the greater the concentration, the stronger the oxidation.
(1) Reacts with metals.
Chemical equation for the reaction of dilute nitric acid with copper:
3Cu+8HNO3(diluted)===3Cu(NO3)2+2NO↑+4H2O.
Chemical equation for the reaction of concentrated nitric acid with copper:
Cu+4HNO3(concentrated)===Cu(NO3)2+2NO2↑+2H2O.
(2) Reacts with non-metals.
For example, the chemical equation for the reaction of concentrated nitric acid with C:
C+4HNO3 (concentrated) △, CO2↑+4NO2↑+2H2O.
(3) Reacting with reducing compounds.
Nitric acid can oxidize reducing substances such as H2S, SO2, Na2SO3, HI, Fe2+, etc.
For example, the ionic equation for the reaction of dilute nitric acid with FeSO4 solution is:
3Fe2＋＋4H＋＋NO3－===3Fe3＋＋NO↑＋2H2O。
Investigation point 1 Comparison of oxidation properties of concentrated and dilute nitric acid
1. According to the chemical equation of the reaction between copper and nitric acid, concentrated nitric acid is reduced to NO2, and the valence change of nitrogen element is +5→+4; Diluted nitric acid is reduced to NO, and the valence of nitrogen changes to +5→+2. In general, the smaller the concentration of nitric acid, the lower the valence state of its reduction product.
2. Experiments have proved that the greater the concentration of nitric acid, the stronger the ability to obtain electrons, and therefore its oxidation ability. For example, dilute nitric acid can oxidize HI to I2, while concentrated nitric acid can oxidize HI to HIO3.
6HI+2HNO3(diluted)△3I2+2NO↑+4H2O
HI+6HNO3 (concentrated) △HIO3+6NO2↑+3H2O
3. Nitric acid in redox reaction, its reduction products may have a variety of valence substances: +4NO2, HN+3O2, +2NO, +1N2O, 0N2, -3NH3, etc., depending on the concentration of nitric acid and the strength of the reducing agent. In addition to the previous example, zinc and nitric acid can react as follows:
4Zn+10HNO3(diluted)===4Zn(NO3)2+N2O↑+5H2O
4Zn+10HNO3(extremely rare)===4Zn(NO3)2+NH4NO3+3H2O
4. The law of reaction between nitric acid and metal:
(1) HNO3 reacts with metals to produce H2.
(2) The reduction products are generally HNO3 (concentrated) → NO2, HNO3 (diluted) → NO; Very dilute nitric acid reduction products may also be N2O, N2 or NH4NO3.
(3) Nitric acid shows both oxidation and acidity when it reacts with metals.
Investigation point 2 Calculation of the reaction of nitric acid with metals
1. Thought flow
2. Application of conservation ideas in computing
(1) Conservation of atoms:
When HNO3 reacts with metals, a part of HNO3 acts as an acid and exists in solution in the form of NO3-; Part of it is used as an oxidizing agent and converted into a reduction product. The total amount of nitrogen atoms in these two parts is equal to the amount of matter of nitrogen atoms in HNO3 consumed by the reaction.
(2) Electronic conservation of gain and loss:
The reaction of HNO3 with metals is a redox reaction, and the amount of material in which nitrogen atoms obtain electrons in HNO3 is equal to the amount of substances in which metals lose electrons.
(3) Conservation of charge method:
In excess of HNO3, the solution after the reaction (without considering OH-) is:
c
(NO3－)＝
(H＋)＋
nc
(M
n
＋)(M
+ stands for metal ions).
(4) Ion equation calculation method:
When the metal reacts with the mixed acid of H2SO4 and HNO3, because NO3- in nitrate can continue to react with the metal under the condition that H2SO4 provides H+, such topics should be calculated by the ionic equation, first make an excess judgment, and then make relevant calculations according to the fully reacted metal or H+ or NO3-, and the solution should conform to the conservation of charge.
c
n