CALCIUM NITRATE (CA (NO3) 2): STRUCTURE, PROPERTIES AND USES - CHEMISTRY - 2024

The calcium nitrate is a tertiary inorganic salt having the chemical formula Ca (NO ₃) ₂. From its formula it is known that its solid is composed of Ca ²⁺ and NO ₃ ^- ions in a 1: 2 ratio. Therefore, it is a compound of purely ionic nature.

One of its properties is its oxidizing character, due to the nitrate anion. It is not combustible, that is, it does not burn at high temperatures. Being non-combustible, it represents a safe solid to handle without much care; however, it can accelerate the ignition of combustible materials.

Solid calcium nitrate. Source: Ondřej Mangl, from Wikimedia Commons

Its appearance consists of a granular solid, which has a white or light gray color (upper image). It can be anhydrous or tetrahydrate, Ca (NO ₃) ₂ · 4H ₂ O. It is very soluble in water, methanol and acetone.

Calcium nitrate has been widely used as a fertilizer, as it moves easily in moist soil, and is quickly absorbed by plant roots. It supplies two important elements for plant nutrition and growth: nitrogen and calcium.

Nitrogen is one of the three essential elements for the development of plants (N, P and K), it is essential in the synthesis of proteins. Meanwhile, calcium is necessary to maintain the structure of the cell wall of plants. For this reason Ca (NO ₃) ₂ is used a lot in gardens.

On the other hand, this salt has toxic actions, especially by direct contact with the skin and eyes, as well as by inhalation of its dust. In addition, it can be decomposed by heating.

Structure of calcium nitrate

Ions of calcium nitrate. Source: Я.HarDNox at ru.wikipedia, from Wikimedia Commons

The upper image shows the structure of Ca (NO ₃) ₂ in a spheres and bars model. Here, however, there is a defect: the existence of Ca-O covalent bonds is assumed, which contradicts their ionic character. Clarifying this, really the interactions are of the electrostatic type.

The Ca ²⁺ cation is surrounded by two NO ₃ anions ^- according to their proportions in the crystal. Therefore, nitrogen predominates in the form of nitrate in the crystalline structure.

The ions are grouped in such a way that they establish a configuration whose minimum expression is the unit cell; which, for the anhydrous salt, is cubic. In other words, from cubes containing the 1: 2 ratio for these ions, the entire crystal is reproduced.

On the other hand, the tetrahydrated salt, Ca (NO ₃) ₂ · 4H ₂ O, has four water molecules for each set of NO ₃ ^- Ca ²⁺ NO ₃ ^-. This modifies the crystal structure, deforming it into a monoclinic unit cell.

Therefore, the crystals for both the anhydrous and the tetrahydrate salts are expected to be different; differences that can be determined in their physical properties, eg, melting points.

Physical and chemical properties

Chemical names

-Calcium nitrate

-Calcium dinitrate

-Nitrocalcite

-Norwegian saltpeter and limesaltpetro.

Molecular formula

Ca (NO ₃) ₂ or CaN ₂ O ₆

Molecular weight

Anhydrous 164.088 g / mol and tetrahydrate 236.15 g / mol. Note the effect of water on molecular weight, and it cannot be neglected when weighing it.

Physical appearance

White or light gray solid or granules. Cubic white crystals or deliquescent granules; that is, they absorb moisture to the point that they dissolve as a result of their high solubility.

Boiling point

The anhydrous form decomposes on heating to a temperature that prevents the determination of its boiling point; whereas the tetrahydrate form of the salt has a boiling point of 132ºC (270ºF, 405K).

Melting point

-Anhydrous form: 561 ° C to 760 mmHg (1042 ° F, 834 K).

-Tetrahydrate form: 42.7 ° C (109 ° F, 316 K).

This shows how water molecules interfere with electrostatic interactions between Ca ²⁺ and NO ₃ ^- inside crystals; and consequently, the solid melts at a much lower temperature.

Water solubility

-Anhydrous form: 1212 g / L at 20 ºC.

-Tetrahydrate form: 1290 g / L at 20 ºC.

The water in the crystals hardly increases the solubility of the salt.

Solubility in organic solvents

-In ethanol, 51.42 g / 100 g at 20 ºC.

-In methanol, 134 g / 100 g at 10 ºC.

-In acetone, 168 g / 100 g at 20 ºC.

Acidity (pKa)

6.0

Density

2.5 g / cm ³ at 25 ° C (tetrahydrate).

Decomposition

When calcium nitrate is heated to incandescence, it decomposes into calcium oxide, nitrogen oxide, and oxygen.

Reactive profile

It is a strongly oxidizing agent, but it is not combustible. Accelerates the ignition of combustible materials. The division of calcium nitrate into fine particles facilitates its explosion when the compound is exposed to prolonged fire.

Mixtures with alkyl esters become explosive by originating alkyl nitrate esters. The combination of calcium nitrate with phosphorus, tin (II) chloride or other reducing agent, can react explosively.

Applications

farming

It is used in crops as a source of nitrogen and calcium. Calcium nitrate is very soluble in water and easily absorbed by the roots of plants. Furthermore, it does not acidify soils because its ions cannot be significantly hydrolyzed.

Mixing it with fertilizers containing phosphorus or sulfate should be avoided to avoid the formation of insoluble salts. Due to its hygroscopicity, it must be stored in a dry and cool environment.

Its use has an advantage over the use of ammonium nitrate as a fertilizer. Although the latter compound contributes nitrogen to plants, it interferes with calcium absorption, which could lead to calcium deficiency in plants.

Calcium contributes to the maintenance of the cell wall structure of plants. In the presence of a calcium deficiency, the growing tissues of plants, such as root tips, young leaves, and shoot tips, often show distorted growth.

Decreased ammonia

Calcium nitrate reduces the accumulation of volatile fatty acids and phenolic compounds, phytotoxic that accumulate due to the decomposition of soybean crop residues.

Furthermore, there is a tendency for calcium nitrate to decrease the ammonium concentration in the soil, which increases the hydrogen buffering capacity.

Concrete

Calcium nitrate is used to reduce the setting time of concrete. This is produced by the generation of calcium hydroxide, perhaps through a double displacement reaction.

In addition, calcium nitrate induces the generation of the iron hydroxide compound, whose protective action on concrete reduces its corrosion. That is, the iron present can react with the basic components of concrete, such as calcium hydroxide itself.

Calcium nitrate decreases the setting time, as well as the resistance of the concrete, to which volcanic ash has been added. To study the effect of adding calcium nitrate to concrete, increasing concentrations of calcium nitrate have been used, between 2% and 10%.

A greater decrease in setting time has been observed, as well as an increase in concrete strength as the calcium nitrate concentration increased up to 10%.

Sewage or wastewater treatment

Calcium nitrate is used to reduce bad odors from sewage by reducing the generation of hydrogen sulfide. In addition, the organic matter that generates anaerobic conditions is consumed, which makes it difficult for many biological species to survive.

Preparation of cold compresses

Calcium nitrate tetrahydrate is an endothermic compound, that is, it has the ability to absorb heat from the surrounding environment. This produces a cooling of the bodies that come into contact with the containers that contain it.

The compresses increase their temperature, and to regenerate them it is enough to place them in a freezer

Latex coagulation

Calcium nitrate is used in the latex coagulation phase. It is part of the immersion solution, and when it comes into contact with the solution containing the latex, it breaks its stabilization and causes it to coagulate.

Heat transfer and storage

The binary mixture of molten nitrate salts, including calcium with other nitrates, is used in place of thermal oil in solar power plants for heat transfer and storage.

Forms of application

-Calcium nitrate is applied mixed with the soil at a concentration of 1.59 kg per 30.48 m ², with adequate irrigation. Calcium nitrate is solubilized in water, allowing its absorption by the roots of the plant. In hydroponic crops it dissolves in the growing water.

-Calcium nitrate is also used in the form of a spray to spray the leaves and flowers, being an effective treatment in the prevention of the rotting of the tomato flower, the cork stain and the bitter pit of the apple.

-A quantity of calcium nitrate is added to the concrete-forming mixture (cement, sand, stones and water), and the effect that its addition has on the specific properties of the concrete is determined; such as setting speed and strength.

-Calcium nitrate is added at an adequate concentration to reduce the bad odors of sewage or waste water, to a level that the odors are tolerable for people.

References

1. Bonnie L. Grant. (2019). Calcium Nitrate Fertilizer - What Does Calcium Nitrate Do For Plants. Recovered from: gardeningknowhow.com
2. Farquharson, BF, Vroney, RP, Beauchamp, EG and Vyn, TJ (1990). The use of calcium nitrate to reduce phytotoxin accumulation during corp residue decomposition. Canadian Journal of Soil Science 70 (4): 723-726.
3. Ogunbode, EB and Hassan, IO (2011). Effect of addition of calcium nitrate on selective properties of concrete containing volcanic ash. Leonardo Electronic Journal of Practices Technologies 19: 29-38.
4. Wikipedia. (2019). Calcium nitrate. Recovered from: en.wikipedia.org
5. Shiqi Dong & col. (2018). Steel corrosion inhibition by calcium nitrate in halide-enriched completion fluid environments. npj Materials Degradation volume 2, Article number: 32.
6. Emaginationz Technologies. (2019). Calcium Nitrate Specifications. Recovered from: direct2farmer.com
7. PubChem. (2019). Calcium nitrate. Recovered from: pubchem.ncbi.nlm.nih.gov