[Edit this paragraph] Overview
Name: ammonia water
Nickname: ammonium hydroxide; ammonia
English name: ammonium hydroxide; ammonia
Molecular formula: NH3·H2O
Molecular weight: 35.045
Structure: Hydrated ammonia molecules are composed of ammonia molecules and hydrogen provided by water through coordination bonds.
CASNo.: 1336-2 1-6
National standard code: 82503
Danger sign: 20 (alkaline corrosive products)
[Edit this paragraph] Basic nature
Description: Colorless and transparent liquid with strong pungent smell.
Melting point: -77℃
Steam pressure: 1.59 kPa (20 degrees Celsius)
Relative density: The more ammonia content, the smaller the density. The relative density of 28% ammonia water is 0.9 1, and that of 35% ammonia water is 0.88.
Ionization constant: K= 1.8× 10ˇ-5(25℃)
Stability: easy to decompose when heated or exposed to light.
Others: easily volatilize ammonia. Concentrated ammonia can irritate respiratory tract and skin, and can damage central nervous system. It is weakly alkaline.
[Edit this paragraph] Main attributes
volatility
Ammonia is volatilized from ammonia water, and the volatilization rate increases with the increase of temperature and storage time, and the volatilization amount increases with the increase of concentration.
corrosivity
Ammonia water has a certain corrosive effect, and the corrosion of carbonized ammonia water is more serious. Copper is corrosive, steel is poor, and cement is not corrosive. It also has a certain corrosive effect on wood.
alkalescence
The following chemical equilibria exist in ammonia water:
NH3+H2O= (reversible) = NH3 H2O
NH3 H2O = (reversible) =NH4+ +OH-
Therefore, only a small part of ammonia molecules react with water to generate ammonium ion NH4+ and hydroxyl ion OH-, so it is weakly alkaline.
Ammonia has the commonness of alkali:
① It can make colorless phenolphthalein test solution turn red, purple litmus test solution turn blue and wet red litmus test paper turn blue. This method is often used to test the presence of NH3 in the laboratory.
② It can react with acid to generate ammonium salt. When concentrated ammonia meets volatile acids (such as concentrated hydrochloric acid and concentrated nitric acid), it will produce white smoke.
NH3+HCl=NH4Cl (white smoke)
NH3+HNO3=NH4NO3 (white smoke)
But in the case of non-volatile acids (such as sulfuric acid and phosphoric acid), this phenomenon does not exist. This method can be used to test the presence of NH3 or ammonia in the laboratory.
In industry, the weak alkalinity of ammonia water is used to absorb the tail gas of sulfuric acid industry to prevent environmental pollution.
SO2+2NH3 H2O = (NH4) 2SO3+H2O (NH4) 2SO3+SO2+H2O = 2nh4SO3 Ammonia is very soluble in water.
unstable
[2] Ammonia monohydrate is unstable and easy to decompose when exposed to light, resulting in ammonia and water.
NH3 H2O=NH3↑+H2O
In the laboratory, ammonia can be produced by heating concentrated ammonia or mixing concentrated ammonia with solid caustic soda at room temperature. The device and operation are simple, and the ammonia concentration obtained is high, so the experiment effect of "fountain" is better.
Because ammonia water is volatile and unstable, it should be sealed in brown or dark reagent bottle and stored in a cool and dark place.
subside
Ammonia reacts with Fe2+ to form precipitate [3] Ammonia is a good precipitant, which can react with various metal ions to form insoluble weak base or amphoteric hydroxide. For example:
Al3++3NH3 H2O==Al(OH)3↓+3NH4+
The generated Al(OH)3 precipitate is insoluble in excessive ammonia water.
Fe2+2NH3 H2O==Fe(OH)2↓+2NH4+
The generated white precipitate is easily oxidized to generate reddish-brown precipitate.
4Fe(OH)2+O2+2H2O=4Fe(OH)3 (reddish brown)
Using this property, aluminum hydroxide, iron hydroxide and iron hydroxide can be prepared in experiments.
complexity
Ammonia can react with Ag+, Cu2+, Cr3+ and Zn2+ plasmas. Insoluble weak base is formed when the amount of ammonia water is small. When ammonia water is excessive, insoluble matter is converted into complex ions and dissolved.
Silver oxide +4 ammonia H2O = 2[ silver (ammonia) 2]++2OH-+3H2O
This reaction was used to prepare silver ammonia solution in the laboratory.
Zn(OH)2+4 NH3·H2O =[Zn(NH3)4]2 ++ 2OH-+4H2O
This reaction can be used to identify amphoteric hydroxides, aluminum hydroxide and zinc hydroxide.
Cu (OH) 2+4NH3 H2O = [Cu (NH3) 4] 2+(dark blue) +2OH-+4H2O
reducing power
Ammonia is weakly reducible and can be oxidized by strong oxidant. If ammonia water can react with chlorine water:
3c L2+8 NH3·H2O = 6 NH4Cl+N2+8H2O
It can also react with KMnO4.
[Edit this paragraph] Packaging, storage and transportation
Shipment in sealed glass bottles, cans, iron drums, tankers or tankers. It should be stored in a cool, sheltered and fireproof place to reduce ammonia volatilization and avoid explosion accidents.
Ammonia has strong irritation, so attention should be paid to prevent it from irritating eyes, burning skin, causing dyspnea or strong suffocating cough during storage and transportation. The vehicle has small self-importance, large loading capacity, good sealing performance, strong corrosion resistance, durability and convenient loading and unloading.
[Edit this paragraph] Preparation or source
Its source can be the products of synthetic ammonia plant, or it can be specially prepared with liquid ammonia or gaseous ammonia and water.
In addition to synthetic ammonia plants, coking plants, coal dry distillation and petroleum industries can also produce ammonia water with different concentrations as by-products.
It is also possible to use the ammonia-containing tail gas in the ammonia processing process of nitrogen fertilizer plant to produce dilute ammonia water after being absorbed by water. The nitrogen content is 1% ~ 3%, which is low in price and suitable for nearby application.
In order to minimize the volatilization loss of ammonia during storage, transportation and use, at present (in 2008), a certain amount of carbon dioxide is often injected into ammonia water to carbonize it, so that part of ammonia is combined with carbon dioxide to form a mixed solution containing NH4HCO3, (NH4)2CO3 and NH3·H2O, which is called "carbonized ammonia water". Compared with ordinary ammonia water, carbonized ammonia water can obviously reduce ammonia volatilization.
[Edit this paragraph] Agricultural use
The ammonia concentration of agricultural ammonia water is generally controlled within the range of nitrogen content 15% ~ 18%, and carbonation determination is better than 100%. Fertilization is very simple, and there are many methods, such as furrow application, surface application, application with irrigation water or spraying application. When using, it must be diluted to less than one thousandth with water, and contact with stems and leaves is prohibited to avoid scalding.
The application principle of ammonia water is "never leave soil, never leave water". Not leaving the soil is to cover the soil deeply; When there is no water, dilute it with water to reduce concentration and volatilization, or combine it with irrigation. Because ammonia water is lighter than water, attention should be paid to avoid excessive accumulation and burning plants in local areas during irrigation. Ammonia can be used as base fertilizer or topdressing.
The ammonia concentrations commonly used in China are 15%, 17% and 20%. The concentration of agricultural ammonia in foreign countries is slightly higher, and the products generally contain 25% ammonia (20% nitrogen).
In 2008, the output of ammonia water in China was less than 0.2% of the total output of nitrogen fertilizer.
[Edit this paragraph] Other purposes
Ammonia is an important reagent in the laboratory. For its main usage, please refer to the section "Main Attributes".
As an alkaline disinfectant in the army, it is used to disinfect sarin. Commonly used is 10% dilute ammonia water (density 0.960), and the concentration used in winter is 20%.
Inorganic industry is used to prepare various iron salts.
Wool spinning, silk, printing and dyeing industries are used for washing, dissolving and adjusting pH value of wool, woolen cloth and grey cloth, and as dyeing auxiliaries.
Organic industry is used as aminating agent and catalyst for producing thermosetting phenolic resin.
In medicine, dilute ammonia water is used for reflexively stimulating breathing and circulation, treating syncope and syncope, and also as skin irritant and disinfectant.
Also used as detergent, neutralizer and alkaloid leaching agent. It is also used in pharmaceutical industry, gauze cover industry, photo printing and so on.
[Edit this paragraph] Impact on the environment
I. Health hazards
Invasion route: inhalation and ingestion.
Health hazards:
Stimulate the nose, throat and lungs after inhalation, causing cough, shortness of breath and asthma; Can die of laryngeal edema and suffocation; Pulmonary edema will occur, leading to death. If ammonia water spills into eyes, if emergency measures are not taken, it may cause corneal ulcer and perforation, further cause eye inflammation, and eventually lead to eyeball atrophy and blindness.
Skin contact can cause burns.
Chronic effects: Repeated low-concentration contact can cause bronchitis. Repeated contact with the skin can cause dermatitis, which is characterized by dryness, itching and redness.
Second, toxicological data and environmental behavior.
Toxicity: low toxicity.
Acute toxicity: LD50350mg/kg (oral) in rats.
Hazard characteristics: easy to decompose and release ammonia. The higher the temperature, the faster the decomposition rate and the explosive atmosphere can be formed. In case of high heat, the internal pressure of the container rises, which is in danger of rupture and explosion.
Combustion (decomposition) product: ammonia.
Third, on-site emergency monitoring methods
Detection tube method
Four, laboratory monitoring methods
Nessler's reagent colorimetry (GB7479-87)
Salicylic acid spectrophotometry (GB748 1-87)
Verb (abbreviation of verb) environmental standard
China (GB/T 14848-93) Groundwater Quality Standard (ammonia nitrogen, mg/L)
0.02 for one class, 0.02 for two classes, 0.2 for three classes, 0.5 for four classes and 0.5 for five classes.
China (GB 1 1607-89) Fishery Water Quality Standard (Nonionic Ammonia)
0.02 mg/l
China (GHZB 1- 1999) Environmental Quality Standard for Surface Water (ammonia nitrogen, mg/L)
A class of 0.5; Class Ⅱ 0.5; Class ⅲ 0.5; Class ⅳ1.0; Class v 1.5
Environmental quality standard for surface water (nonionic ammonia, mg/L)
A class of 0.02; Class Ⅱ 0.02; Class ⅲ 0.02; Class Ⅳ 0.2; V level 0.2
China (GB3097- 1997) Seawater Quality Standard (Nonionic Ammonia)
0.020 mg/l
China (GB5048-92) Water Quality Standard for Farmland Irrigation (Kjeldahl Nitrogen)
Hydroponics:12mg/l
Dry farming: 30mg/L.
Vegetables: 30mg/L.
China (GB8978- 1996) Integrated Wastewater Discharge Standard (ammonia nitrogen) Pharmaceutical raw materials, dyes and petrochemical industry.
Grade I15mg/l; Middle school 50 mg/L
Other pollutant discharging units
Grade I15mg/l; Secondary school 25 mg/l