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Hyponitrous Acid Formula plays a significant role in a catalytic reaction where it acts as hyponitrite reductase and an isomer of nitramide. It can be synthesized from anhydrous hydrochloric acid (HCl) and silver (I) hyponitrite in the presence of an ether medium. In addition, it can be synthesized through the oxidation of hydroxylamine or the reduction of nitrates. The name "hypo" itself reflects that the acid has less nitrous content and so-called weak diprotic acid. The elements such as oxygen and nitrogen in "p-block" combine with hydrogen in "s-block" to form this acid structure. Further, its hydrogen bond donor and hydrogen acceptor has 2 and 4 electron sharing properties.
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Key Terms: Hyponitrous acid, p-block elements, hyponitrite, acids, explosive
Hyponitrous Acid Preparation
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The hyponitrous acid can be synthesized through treating a reaction with a silver (I) hyponitrite (Ag2N2O2) and anhydrous hydrochloric acid (HCl) in the presence of ether medium. The reaction can be understood from the below equation.
Ag2N2O2+2HCl→ H2N2O2+2AgCl
Here, in this reaction, the ether evaporates and produces solid H2N2O2, but the acid (silver chloride) remains unstable leading to a continuous chain of explosion. Further, the acid decomposes in an aqueous solution to form anhydride of hyponitrous acid through the following reaction as follows:
H2N2O2→ H2O+ N2O
In the above reaction, the N2O is anhydrite and the acid cannot be prepared using an aqueous solution (water). Therefore, the hyponitrous acid is treated with air to obtain nitric and nitrous acid through the reaction below:
2 H2N2O2 + 3 O2→ 2 HNO3+ 2 HNO2
Finally, to obtain hyponitrite salts, the nitrate or nitrite undergoes a reduction reaction with sodium amalgam as a catalyst in a water medium. The reaction results in the formation of Cis and Trans structure of hyponitrous acid.
2D and 3D View of Hyponitrous Acid
Hyponitrous Acid Formula
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The chemical formula for hyponitrous acid can be denoted in three various forms
- H2N2O2 (Molecular Form)
- HON=NOH (Linear Form)
- N(=NO)O (SMILES Form)
*SMILES = Simplified molecular and input line-entry system
Hyponitrous Acid Properties
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Physical Property
Hyponitrous Acid Structure
Cis and Trans form of Hyponitrous Acid
Hyponitrous acid has two possible structures which are Trans and cis. The structures were
- Sodium Salt obtained from Cis hyponitrous acid and,
- White crystals obtained from trans-hyponitrous acid
Chemical Property
| Terms | Properties |
|---|---|
| IUPAC Name | Diazenediol |
| Chemical Formula | H2N2O2 |
| 62.0282 g/mol | |
| Physical Appearance | White Crystals |
| Conjugate base | Hyponitrite |
| H-Bond Acceptors | 4 |
| H-Bond Donors | 2 |
| Other Name | Hyponitrous acid dimer |
Hyponitrous Acid Safety Precautions
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We must be careful while handling white crystals (obtained from trans-hyponitrous acid) because it has an explosive nature. In addition, the acid is so weak it decomposes in an aqueous solution to form nitrous oxide.
Hyponitrous Acid Applications
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The hyponitrous acid has a significant role in enzymology, where it acts as a hyponitrite reductase enzyme that catalyzes the chemical reaction.
Things to Remember
- Hyponitrous acid is a colorless crystalline produced from anhydrous hydrochloric acid (HCl) and silver (I) hyponitrite in ether.
- Hyponitrous acid has 4 H-bond acceptors and 2 H-Bond donors.
- Hyponitrous acid exists in two possible structures: Cis and Trans in the form of respective sodium salt and white crystals.
- White crystals (Trans) are explosive in dry conditions due to their unstableness.
- Hyponitrous acid plays a key role in a catalytic enzymatic reaction as a hyponitrite reductase enzyme.
Sample Questions
Ques. Write the Molecular bonding structure of hyponitrous acid. (1 Mark)
Ans. HO-N=N-OH
Explanation : In the above molecular structure, hydrogen and oxygen share a single bond with nitrogen as they have a single valence electron whereas nitrogen forms three bonds due to its three valence electrons (one bond with one hydroxyl group and two bonds with neighbour nitrogen atom). The proper bonding between any molecular structure defines its stability.
Ques. Write the reaction to prepare hyponitrous acid. (2 Mark)
Ans. To prepare hyponitrous acid, we need to react to anhydrous hydrochloric acid (HCl) with a silver (I) hyponitrite in an ether medium. The reaction can be written as follows:
Ag2N2O2+2HCl→ H2N2O2+2AgCl
The above reaction undergoes decomposition of silver (I) hyponitrite and hydrochloric acid, where 2 moles of silver react with 2 moles of chloride to form silver chloride. On the other side, nitrogen, oxygen, and hydrogen combine to form hyponitrous acid.
Ques. What is the oxidation state of nitrogen in hyponitrous acid? (2 Mark)
Ans. We know that nitrogen has a positive charge in hyponitrous acid which is H2+N2+O2-. So, the oxidation state of nitrogen is +1.
Hyponitrous acid has four Cations ( 2 H-Cations + 2 N-Cations = 4 Cations (Ions)) and 2 Anions (which is Oxygen ions). So, the oxidation of nitrogen in hyponitrous acid is +1. The easiest way or rules to determine the oxidation state of any element can be found in Oxidation, Reduction, and Redox Reaction.
Ques. Which of the following acids can form two types of salts? (2 Mark)
A) Nitrous Acid
B) Nitric Acid
C) Pernitric Acid
D) Hyponitrous Acid
Ans. Option (D) – Hyponitrous Acid. Because it forms two types of salt in Cis and Trans form which is sodium and white crystal.
Explanation: From the above options (A) and (B) were the residue or reduced from the hyponitrous acid during the preparation, so it cannot form any type of salt. Then, the option (C) – pernitric acid has one hydrogen and nitrogen atom with four oxygen molecules (HNO4), hence it cannot form a salt. Therefore, the last option remains in option (D), hyponitrous acid which forms two types of salts in Cis and Trans form.
Ques. How many hydroxyl groups are present in hyponitrous acid? (1 Mark)
Ans. The formula for hyponitrous acid is H2N2O2 which can also be written as N2 (OH)2 or OH-N=N-OH. So, from the second & third form, we can observe that the number of hydroxyl groups (OH) present on either side of the nitrogen atom is 2. Hence, the answer is two hydroxyl groups.
Ques. What is the sum of oxidation states of nitrogen in hyponitrous, nitric and nitrous acid? (3 Mark)
Ans. Hyponitrous acid can be written as N2 (OH)2
2n+ 2(-1) = 0
2n = 2
n = 1
For nitric acid: HNO3
1 + n + 3(-2) = 0
n = +5
For nitrous acid: HNO2
1 + n + 2(-2) = 0
n = +3
Then finally, the sum of oxidation state = 1 + 5 + 3 = 9
Explanation: To find the oxidation state of any compounds follows the rule here. So, to find the oxidation state of the N-atom in hyponitrous acid: we have a sum of 2n atoms and 2(-1) molecules. Then, equating to zero, we get n = 1. Similarly, the corresponding oxidation state of nitrogen in nitric and nitrous acid, we get n = +5 and n = +3 respectively. Finally, adding all the oxidation states, we get a sum of n = 9.
Ques. Draw the structure of hyponitrous acid. (2 Mark)
Ans. To draw the structure, we must have a proper understanding of the position of atoms or molecules in hyponitrous acid (Ref-Fig1). At first, instant, write down the groups or atoms of hyponitrous acid in a zig-zag pattern in the order of (HO-N=N-OH), then stabilize the structure with proper bonding (two bonds between nitrogen atoms and one bond between each hydroxyl group).
Ques. Which form of hyponitrous salt is explosive in dry form? (2 Mark)
Ans. Trans-hyponitrous acid (White Crystalline Salt)
We know that reduced Trans-hyponitrous acid (white crystals) remains unstable during the reduction process in a dry form, resulting in explosive nature. Further, to attain stability, it decomposes in an aqueous solution to give out nitric acid. So the answer is Trans-hyponitrous acid.
Ques. Write down the reactions to prepare the following compounds. (4 Mark)
Ans. Ag2N2O2+2HCl→ H2N2O2+2AgCl
Explanation: To prepare hyponitrous acid, we need to react anhydrous hydrochloric acid with silver (I) hyponitrite in an ether medium, where the reaction undergoes oxidation and reduction reaction to give out hyponitrous acid and silver chloride.
- Nitrous acid
Ans. 2 H2N2O2 + 3 O2→ 2 HNO3+ 2 HNO2
Explanation: Reducing nitrous acid from hyponitrous acid is unfeasible because the N2O is anhydrite (obtained from H2N2O2 decomposition). So the nitric acid cannot be prepared in association with an aqueous solution. Therefore, the acid is treated with air to give out nitric and nitrous acid.
Ques. Identify the correct hyponitrous acid. (1 Mark)
N2O5
H2N2O2
HNO2
HNO3
Ans. Option (B) H2N2O2
Explanation: Firstly we have to identify all the compounds, given that, will consider the option (C) and (D), where it's the nitrous and nitric acid. Secondly, option (A) is nitric anhydrite. So, the last option is (B) is the correct answer which is hyponitrous acid.
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