Acids, Bases and Salts

Nitric Acid

Nitric Acid belongs to the category of a strong acid. Some other popular names of it are the spirit of nitre as well as the aqua fortis. In its pure form, it appears as the colourless. And with the passage of time, it gets older and hence it turns into the yellow cast. This colouration is happening due to the decomposition of Nitric acid to oxides of nitrogen and water. Nature of Nitric Acid is highly corrosive and toxic. It may cause severe skin burn too. It easily reacts with hydroxides, metals, and oxides to produce the nitrate salts. Therefore, it is useful as a strong oxidizing agent.

It can be produced through the catalytic oxidation of ammonia. It is a generic reagent used in laboratories and an important chemical used in many industries to manufacture explosives and fertilizers. The PH of Nitric acid is approximately 3.01. This article will explain the concept of Nitric Acid.

Nitric Acid

                                                                                               Nitric Acid

Structure of Nitric Acid Molecules

The molecular formula of Nitric acid is  \(HNO_{3}\). It’s one molecule contains 3 oxygen atoms, 1 nitrogen atom, and 1 hydrogen atom. In its molecules, one of the oxygen atoms is doubly bonded to the nitrogen atom at the centre. Also, another oxygen atom is singly bonded to the central nitrogen atom as well as to the hydrogen atom. The last oxygen atom in the nitric acid molecule is having negative charge of -1 and it is singly bonded to the central nitrogen atom.

As the nitrogen atom at the centre of the molecule participates in four covalent bonds (i.e. with 3 oxygen atoms). So, it has a charge of the positive value of +1. Thus, the net charge on the nitric acid molecule becomes zero, because the positive charge on the nitrogen atom and the negative charge on the oxygen atom cancels each other out. It must be remembered that the charges in these molecules can be delocalized due to the resonance effect.

The shape of Nitric acid molecule is planar, with the nitrogen atom attached to three oxygen atoms, one of which holds the proton. Other two N-O bonds are equivalent and show the resonance with double bond character.

Preparation of Nitric Acid

The nitric oxide (i.e. NO) is the by-product. It usually gets oxidized again by the oxygen present in the air. Further, it produces additional nitrogen dioxide starting material. For commercial purposes, production of nitric acid is done through the oxidation process of the anhydrous ammonia to nitric oxide. This reaction needs the presence of a platinum catalyst at the high temperature. It is the Ostwald process.

A more volatile acid can be easily displaced from its salt through the other one having less volatile acid. This basic principle is very useful in the preparation of nitric acid in the laboratory. This acid is more volatile acidic in comparison to sulphuric acid. Hence, it is generally displaced by the sulphuric acid from metal nitrates.

50gm of the potassium nitrate (i.e. \(KNO_{3}\) and 25ml of concentrated sulphuric acid ( i.e. \(H_{2}SO_{4}\) is required in a round bottom flask. This set of reactants are heated to about 200 C. But temperature must not be more than 200 C. Its chemical equation is:

\(KNO_{3} + H_{2}SO_{4} \rightarrow KHSO_{4} + HNO_{3}\)


Physical properties

  1. Nitric acid is found as a liquid having the acrid, pungent and suffocating odour.
  2. There are various concentrations of nitric acid available. These are colourless, yellow or red according to the concentration
  3. The industrial-grade is approximately 68% in water, commercial grade is approximately between 52% and 68%.
  4. Also, the fuming nitric acid is approximately 86% or higher, whereas concentrations above 95% are white fuming or red fuming nitric acid.
  5. The PH value of Nitric acid is approximately 3.01.
  6. Its molar mass is 63.01 g/mol and density is \(1.51 g/cm^{3}\).
  7. Its boiling point is  \(83^{0}C\) and its melting point is \(-42)^{0}C\).

Chemical properties

  1. Nitric acid is strong and monoprotic acid.
  2. It turns blue litmus red. It frequently forms solid hydrates like monohydrate \(HNO_{3}·H_{2}O\) and the trihydrate \(HNO_{3}·3H_{2}O\).
  3. With the help of heat or light, it can decompose easily to form brown nitrogen dioxide. Due to this reason, it becomes brownish over time though fresh nitric acid is colourless.
  4. This chemical reaction is: \(4HNO_{3} \rightarrow  2H_{2}O + 4NO_{2} + O_{2}\)
  5. It is having the nature of a powerful oxidizing agent. It reacts violently with many non-metallic compounds. Also, it reacts with metals and metals dissolve in it to produce metal oxides.
  6. Nitric acid releases the hydrogen gas with the metals above hydrogen element 0in the metal activity series. Its some such type of reactions are:

\(Mg + 2HNO_{3} \rightarrow  Mg(NO_{3})_{2} + H_{2}\)

\(Mn + 2HNO_{3} \rightarrow  Mn(NO_{3})_{2} + H_{2}\)

Uses of the Nitric Acid

  1. Nitric acid is very and widely used for the production of fertilizers like ammonium nitrate and the polymers like Nylon.
  2. It is useful as an excellent nitrating agent (introduces a nitro group) with the combination of sulfuric acid. Also, it is useful as an oxidizer in the liquid-fueled rockets.
  3. It is useful to produce the ammonium nitrates for further manufacturing of plastic, dye, and fertilizers.
  4. Explosives like TNT can be produced using Nitric acid.
  5. It is also useful in the liquid-fuelled rockets as an oxidizer.
  6. In its pure form, it helps to remove the wart.
  7. It is useful as the chemical doping agent in electrochemistry

FAQs about Nitric Acid

Q.1: What is the procedure to identify the nitric acid?

Answer: Nitric acid is the liquid which may be colourless or even in yellow colour. It is having shock and acidic odour. Concentrated nitric acid will emit the nitrogen dioxide and nitrogen oxide gasses. Due to acidic properties, it has a pH value of less than 7. It shows the bitter taste, and sometimes a violent reaction with the other metals.

Q.2: What metals are easily dissolving in nitric acid?

Answer: Some metals and alloys are oxidized by nitric acid. But, when struck by concentrated nitric acid, metals like gold and platinum are not oxidized and certain other metals are passivated. Therefore, by using the mixture of acids or the dilute nitric solution, metals can be dissolved.

Q.3: What neutralizes the acidic nature of nitric acid?

Answer: Sodium bicarbonate neutralizes the nitric acid. Actually, neutralizing one part of nitric acid needs one part of sodium bicarbonate.

Q.4: Can we say that Nitric acid is a strong acid or not?

Answer: Yes. Nitric acid is a type of strong acid. It is a strong acid, as almost all of its molecules dissociate into ions in the solution. This is due to the fact that an acid is termed as strong if its degree of ionization is more than 30 per cent.

Q.5: What are some Health hazards of Nitric acid?

Answer: Nitric acid is the corrosive acid which causes severe skin burns effects. Since it is a strong acid and oxidizer, so it can completely decompose the tissues. Even its dilute forms may cause burns and stain the skin. Its pungent fumes are also very irritating and damaging to the eyes, throat and mucous membranes.

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