Uses of Ammonia

There are many gases in our lives. When some gases are dissolved in water, they will become toxic. Ammonia is one of them. When ammonia is dissolved in water, its toxicity will cause certain irritation and strong corrosiveness to the human eyes, mouth, nose and skin. When working with ammonia, you must protect your body. Once a part of the body comes into contact with ammonia, you must go to the hospital for treatment in time.

Ammonia water, also known as ammonia water, is a water solution of ammonia, which is colorless, transparent and has a pungent odor. The melting point of ammonia is -77°C, the boiling point is 36°C, and the density is 0.91g/cm3. Ammonia is easily soluble in water and ethanol. It is volatile and has the general properties of some alkalies. Ammonia water is made by passing ammonia gas into water. Ammonia is poisonous, irritating and corrosive to the eyes, nose and skin, and can cause suffocation. The maximum allowable concentration in the air is 30 mg/m3. Mainly used as fertilizer.

Industrial ammonia water is an aqueous solution containing 25% to 28% ammonia. Only a small part of the ammonia molecules in the ammonia water reacts with water to form ammonia monohydrate, which is a weak base that only exists in ammonia water. The freezing point of ammonia water is related to its concentration. The commonly used freezing point of 20% (wt) concentration is about -35°C. Neutralization reaction with acid generates heat. There is a risk of fire and explosion. Specific heat capacity is 4.3×103J/kg℃ (10% ammonia water)

Question 2

Composition

Supramolecular: NH3xH2O (there are 4 water molecules directly hydrogen-bonded around the NH3 molecule at the saturated vapor pressure, so x = 4). Among these four hydrogen bonds, the hydrogen bond N???HO, in which the ammonia molecule acts as a "proton acceptor" and causes partial proton transfer and exhibits weak alkalinity, is stronger. The other three hydrogen bonds OH-N, in which the ammonia molecule acts as a "proton donor" but has difficulty in proton transfer, are slightly weaker. In order to highlight the hydrogen bond NH-O that causes partial proton transfer and exhibits weak alkalinity, ammonia hydrates (mainly NH3-4H2O) are always abbreviated as NH3-H2O.

Molecules: NH3, H2O, NH3?H2O

Ions: NH4+, OH- and H+

Among them: H2O (more), NH3 (less), NH4+ (less), OH- (less), H+ (very little), NH3?H2O (more) [1]

volatility

Ammonia water easily volatilizes ammonia gas, and the volatility increases with increasing temperature and prolonged storage time, and the volatility increases with increasing concentration. [2]

Corrosive

Ammonia water has a certain corrosive effect, and carbonized ammonia water is more corrosive. It is more corrosive to copper, less corrosive to steel, and less corrosive to cement. It also has a certain corrosive effect on wood. It is a hazardous chemical, hazard code 82503.

Weakly alkaline

The following chemical balance exists in ammonia water:

NH3+H2O-NH3-H2O

NH3?H2O-NH4+ +OHˉ(reversible reaction) ionization constant: K=1.8×10-5(25℃)

Therefore, only a small part of ammonia molecules react with water to form ammonium ions NH4+ and hydroxide ions OH-, so it is weakly alkaline.

① It can turn colorless phenolphthalein solution into red, purple litmus solution into blue, and wet red litmus paper into blue. This method is often used in laboratories to test for the presence of NH3.

②Can react with acid to form ammonium salt. When concentrated ammonia water meets volatile acids (such as concentrated hydrochloric acid and concentrated nitric acid), white smoke will be produced.

NH3+HCl=NH4Cl (white smoke)

NH3+HNO3=NH4NO3 (white smoke)

However, this phenomenon does not occur when encountering non-volatile acids (such as sulfuric acid and phosphoric acid). Therefore, this method can be used in the laboratory to test the presence of ammonia molecules in water.

In industry, the weak alkalinity of ammonia water is used to absorb sulfuric acid industrial tail gas to prevent environmental pollution.

SO2+2NH3?H2O=(NH4)2SO3+H2O(NH4)2SO3+SO2+H2O=2NH4HSO3