Lewis Structure Bonding Geometry and Crystal Structure of Sodium Nitrate
Sodium nitrate refers to an alkali metal nitrate salt having a chemical formula NaNO3. This chemical compound is also called as Chile saltpetre because vast deposits of the same were previously extracted in Chile, and also to differentiate it from normal saltpetre – potassium nitrate. Moreover, the mineral form of sodium nitrate is also termed as nitrate, nitratine or soda nitre.
Sodium nitrate contains a sodium cation and a nitrate anion Na+ and NO3- respectively. It exists in the form of a highly soluble crystalline solid at room temperature and does not support combustion.
By now, you must have got an idea about what sodium nitrate is, so let us move on with the structure.
Structure of Sodium Nitrate
This compound presents a bond between a single Na+ and NO3- ion. Take a look at the following image to understand the sodium nitrate structure.
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In the NaNO3 Lewis structure, the nitrate anion holds a trigonal planar construction where three atoms of oxygen bonds with a central atom of nitrogen. The –ve charge on nitrate anion gets removed because of resonance. Hence, the atom of nitrogen holds a charge equivalent to +1, and all the oxygen atoms have -2/3 charge each. So, -1 is the total validated charge on NO3-.
Besides the structure of NaNO3, you must also know other aspects of this compound. Let us begin!
Preparation of Sodium Nitrate
Sodium nitrate preparation can be done by neutralising nitric acid with sodium bicarbonate, sodium carbonate or sodium hydroxide. Here are the chemical equations of the mentioned neutralisation reactions:
NaHCO3 + HNO3 -> NaNO3 + H2O + CO2
Na2CO3 + 2HNO3 -> 2NaNO3 + CO2 + H2O
NaOH + HNO3 -> NaNO3 + H2O
An important point to consider for the reaction between nitric acid and sodium hydroxide is that it is highly exothermic. The reason for this is that the former is a strong acid, while the latter is a strong base. So, another method to prepare sodium nitrate is by reacting between sodium hydroxide and ammonium nitrate. The chemical equation for this reaction is as follows:
NH4NO3 + NaOH → NH4OH + NaNO3
Moreover, the reaction between ammonium nitrate and sodium bicarbonate or sodium carbonate is also done to yield sodium nitrate. The reactions are:
Na2CO3 + 2NH4NO3 → (NH4)2CO3 + 2NaNO3
NaHCO3 + NH4NO3 → NH4HCO3 + NaNO3
Let us proceed with the properties of NaNO3
NaNO3 Properties
Properties of sodium nitrate can be categorised into chemical and physical ones.
Chemical Properties
Sodium nitrate has a molar mass of 84.99 grams/mole.
Its density is 2.257 gram / c³.
NaNO3 melting point is 308 degree Celsius.
When this compound is dissolved in H2O (water), it separates into NO3- and Na+.
The boiling point of NaNO3 is 380 degree Celsius.
Sodium nitrate is a potent oxidising agent, and violently reacts with reducing agents.
NaNO3 on heating decomposes explosively.
Physical Properties
It is a white coloured crystalline solid.
NaNO3 holds two structures of crystals, namely trigonal and rhombohedral.
It has a sweet smell.
The solubility of sodium nitrate in water is 91.2 g / 100mL at 25 degree temperature.
Sodium nitrate is hugely soluble in NH3 (ammonia).
Applications of NaNO3
Food
It will be interesting for you to know that uses of sodium nitrate are huge in the food industry. NaNO3 acts as a colour fixative and food preservative for meats and poultry. It does not have any quality similar to antioxidant but is functional when reduced to nitrite. Following are some essential functions of sodium nitrite:
Meat stabilisation
Improvement of meat texture
Development of flavour in cured meat
Removing warmed-over flavour
Antimicrobial
Now you may wonder what foods have sodium nitrite, and what are the foods that contain sodium nitrate?
The answer to your questions is that both sodium nitrate and sodium nitrite are found in bacon, ham, corned beef, salami, hot dogs, smoked salmon, dried fish, pate, pickled pig’s feet, jerky, etc.
Agricultural Use
There is a visible influence of sodium nitrate on plant growth. It is being used as N nutrition source from the middle of the nineteenth century and holds a history of being a productive fertiliser material.
Note: Sodium nitrate is preferably used for growing tobacco that is fertilised using a particular form of nitrate fertiliser.
The initial limiting substance for growth of plants in maximum soils is nitrogen. Consequently, owing to this factor, readily available fertilisers which have nitrogenous content increase the growth of crops materially. After a layman applies sodium nitrate to the soil, he notices the crop growth and in the past many looked upon sodium nitrate as a stimulant. However, it is a wrong concept and must be annihilated.
So, How Sodium Nitrate Should be Applied?
As the compound is fast and thoroughly water-soluble in nature, the soil colloids do not absorb the nitrate ion. Nitrogenous fertilisers should be added early for the crops to utilise. This theory also applies to all other nitrate fertilisers. Severe nitrate loss takes place in drainage water when it is added to sands which have open subsoils. Nitrates get leached quickly.
Vast amounts of nitrates can be put to clays instead of sands, but it must be added according to the utilisation of crops within a considerable time period. Also, when large quantities of NaNO3 are to be applied, it must be done two or more times. By doing this, nitrogen loss by leaching can be reduced and simultaneously, injury to plant roots because of excess soluble salts can be avoided.
Other Uses
Gold refiners make use of sodium nitrate to form hybrid aqua regia which helps in dissolving metals like gold.
This chemical compound is used to enable respiration in facultative microorganisms in wastewater industry. A microorganism genus Nitrosomonas intake nitrate instead of oxygen and multiplies to treat wastewater.
Sometimes, marine aquarists use NaNO3 who utilise techniques of carbon-dosing. This compound helps to increase levels of nitrate in water and enhance the growth of bacteria.
Calcium nitrate and potassium nitrate is mixed with sodium nitrate for the purpose of storing heat and, for transfer of heat in solar power units.
Sodium nitrate also acts as an ingredient in fast cold packs, fireworks oxidiser and replaces potassium nitrate, which is commonly present in black powder.
All these points will answer your thought about what is sodium nitrate used for.
Health Concerns Related to Sodium Nitrate
Some observations suggest that a link has been found between increase in nitrate level and rise in deaths from specific diseases like Alzheimer’s disease, stomach cancer, diabetes mellitus and Parkinson’s disease. This is because nitrosamines have a damaging effect on DNA. Nitrosamines which are formed in cured meats contain sodium nitrate, and it can cause critical diseases like esophageal cancer and gastric cancer. Furthermore, sodium nitrate is also related to colorectal cancer.
One reason for processed meat to increase colon cancer risk is the presence of nitrate in it. When a small quantity of nitrate as a preservative is given to meat, it decomposes to nitrite. Then it reacts with foods rich in protein (like meat) to generate NOCs (nitroso compounds) which are carcinogenic. The nitroso compounds can form during curing of meat or when meat digestion takes place in stomach.
Moreover, sodium nitrates can increase the risk of heart diseases. It can harm the blood vessels, which makes the arteries narrow and hard, resulting in heart disorders.
Although sodium nitrates have a lot of applications, it has several health hazards as well. So, you must consider the content of sodium nitrate in food like processed meat, before having it regularly.
Do It Yourself
Nitrites undergo a reaction with proteins and forms:
a) nitroso compounds b) nitrates c) sulphuric acid d) hydrochloric acid
Which liquid dissolves metals like gold?
a) water b) aqua regia c) acetic acid d) ethanol
If sodium hydroxide is mixed with nitric acid, the reaction is hugely exothermic. So, which alternative compound is reacted with sodium hydroxide instead of nitric acid?
a) ammonium nitrate b) potassium nitrate c) HCL d) nitrogen
By going through the above discussion, you must have understood what is NaNO3 structure, side effects, properties, uses, etc. For more related concepts of Chemistry, you can download the Vedantu app to get access to study materials and online classes.
FAQs on Sodium Nitrate Structure and Molecular Geometry Explained
1. What is the structure of sodium nitrate?
The structure of sodium nitrate consists of Na+ ions and NO3- ions arranged in a three-dimensional ionic lattice. In solid sodium nitrate (NaNO3):
- Each Na+ cation is electrostatically attracted to surrounding NO3- anions.
- The nitrate ion has a trigonal planar geometry.
- The compound forms a crystalline ionic solid due to strong ionic bonding.
2. What is the Lewis structure of the nitrate ion in sodium nitrate?
The Lewis structure of the nitrate ion (NO3-) shows one nitrogen atom bonded to three oxygen atoms with resonance. Key features include:
- Central N atom with three O atoms attached.
- One N=O double bond and two N–O single bonds in any one resonance form.
- A total charge of -1 distributed over the oxygen atoms.
- Three equivalent resonance structures, making all N–O bonds equal in length.
3. What is the geometry of the nitrate ion in NaNO3?
The geometry of the nitrate ion (NO3-) is trigonal planar. According to VSEPR theory:
- The central nitrogen has three bonding regions.
- There are no lone pairs on nitrogen.
- The bond angle is approximately 120°.
4. Is sodium nitrate ionic or covalent?
Sodium nitrate is an ionic compound composed of Na+ and NO3- ions. The bonding includes:
- Ionic bonding between Na+ and NO3-.
- Covalent bonds within the nitrate ion (N–O bonds).
5. How is sodium nitrate formed chemically?
Sodium nitrate is formed by the neutralization of nitric acid with a sodium base such as sodium hydroxide. A common reaction is:
- HNO3(aq) + NaOH(aq) → NaNO3(aq) + H2O(l)
6. What type of crystal structure does sodium nitrate have?
Sodium nitrate has a trigonal (rhombohedral) crystal structure in the solid state. In this structure:
- Na+ ions are arranged regularly in a lattice.
- NO3- ions occupy positions between sodium ions.
- The structure is stabilized by strong electrostatic attractions.
7. What is the hybridization of nitrogen in the nitrate ion?
The nitrogen atom in the nitrate ion (NO3-) is sp2 hybridized. This is because:
- Nitrogen forms three sigma (σ) bonds with oxygen.
- There are three regions of electron density around nitrogen.
- The geometry is trigonal planar.
8. Why are all N–O bonds equal in sodium nitrate?
All N–O bonds in the nitrate ion are equal due to resonance. Although one resonance form shows a double bond and two single bonds:
- The actual structure is a hybrid of three resonance forms.
- The negative charge is delocalized over all three oxygen atoms.
- Each N–O bond has the same intermediate bond order (about 1.33).
9. What is the oxidation state of nitrogen in sodium nitrate?
The oxidation state of nitrogen in NaNO3 is +5. It is calculated as follows:
- Na = +1
- O = −2 each (3 × −2 = −6)
- Let nitrogen = x
- x − 6 = −1 (charge of NO3-)
- x = +5
10. How does sodium nitrate dissociate in water?
Sodium nitrate dissociates completely in water into sodium and nitrate ions. The dissociation equation is:
- NaNO3(s) → Na+(aq) + NO3-(aq)
