|Hint :Any chemical compound can be classified as an acid or a base depending upon the acid-base theory used to describe its nature. Writing the dissociation reaction for the chemical compound in an aqueous medium and ions released would help in the classification.|
Complete Step By Step Answer:
Nitric acid is a strong oxidizing agent with the chemical formula HNO3. It is made up of three elements hydrogen, oxygen, and nitrogen. The pure compound of nitric acid is colorless and has a suffocating odor. . It is used in the manufacture of various organic and inorganic nitrates.
In this article, we will discuss Is HNO3 an acid or base, Is it strong or weak? its conjugate base or acid, etc.
So, Is HNO3 an acid or base? HNO3 is an acid. Because on dissolving in an aqueous solution, it dissociates into two ions (H+ and NO3–), and anything that releases an H+ ion in a solution is considered acid in nature.Name of MoleculeNitric acidChemical formulaHNO3NatureStrong acidConjugate base
NO3–pH value3.01Acidity (pKa)-1.4Solubility in waterCompletely miscible
Page Contents show
1 Why HNO3 act as acid?
2 Is Nitric acid (HNO3) strong or weak?
3 Is HNO3 also act as base?
4 Is HNO3 lewis acid or base?
5 What is the Conjugate acid and base of HNO3
6 Is HNO3 stronger acid than HNO2?
7 Uses of Nitric acid
Why HNO3 act as acid?
According to various acid-base theories, an acid is something that releases a proton or H+ ion on dissolving in an aqueous solution.
In the case of HNO3, it dissociates completely in an aqueous solution to give H3O+ and NO3– ions.
⇒ HNO3 + H2O → H3O+ + NO3−
Here in this reaction, HNO3 donates the proton to H2O and formed NO3– conjugate base. And H2O acts as a base because it accepts the proton from HNO3 and forms H3O+ conjugate acid.
Theories to check whether HNO3 is an acid or base.
1. Arrhenius’s theory for acid:
Arrhenius’s theory state that acid is a substance that gives the H+ ions or increased the amount of hydrogen ion in an aqueous solution.
So, the HNO3 molecule, when dissolving in an aqueous solution it dissociates into H+ ions which quickly form hydronium ions (H3O+). So, we can say, HNO3 is Arrhenius acid.
2. Bronsted-Lowry theory for acid:
It states that a compound is an acid when it donates a proton to another compound and itself forms the conjugate base. And the base is something that accepts the proton from another species and itself forms conjugate acid.
Let’s consider the reaction of HNO3 with H2O.
As per the above reaction, HNO3 donates the proton to H2O and itself forms a conjugate base which is NO3–. Therefore, we can say, in the above reaction, HNO3 acts as Bronsted-Lowry acid, and H2O acts as a Bronsted-Lowry base.
Is Nitric acid (HNO3) strong or weak?
To check If Nitric acid(HNO3) a strong or weak, first we have to take a clear understanding of the differences between strong and weak acids.
A strong acid is generally a compound that dissociates completely or is 100% ionized in a solution to yield H+ ions which means no undissociated acid remains in the solution, all moles of acid completely break off and release a lot of H+ ions.
Example- HCl, HBr, H2SO4, HI, HClO4, etc.
And weak acid is generally a compound that is partially or not ionized completely in a solution which means some moles of acid remain undissociated in the solution and do not break completely into ions.
Examples of weak acids- Hydrocyanic acid(HCN), Acetic acid(CH3COOH), Ammonium ion (NH4+), Phosphoric acid(H3PO4), HNO2, HF, HCOOH, H2CO3, etc.
Now, Is HNO3 (Nitric acid) strong or weak? Nitric acid (HNO3) is a strong acid. Because when it is dissolved in an aqueous solution, it completely dissociates into H+ and NO3– ions in the solution.
As on dissolving HNO3 in an aqueous solution, no hydrogen remains bound, all are dissociated and converted into H+ ions which means the concentration of hydrogen ions increased in the solution. Hence, we can say, HNO3 is a strong acid or act as a strong acid.
Note: In diluted form, HNO3 is weak but in concentrated form, it is a very dangerous or strong acid.
As per the above picture, when HNO3 dissolves in an aqueous solution, it completely ionizes or dissociates into H+ and NO3– ions. No undissociated parts of it remain in the solution, all parts completely break off and are ionized in an aqueous solution. the presence of high proton ions in the solution shows the strong ability of HNO3 acid.
The single arrow used in the above reaction shows that only a forward reaction will take place. As NO3– is the very weak conjugate base of HNO3, so it has no power to reform with H+ splitting ion in an aqueous solution and produce an HNO3 molecule again.
Hence, only splitting ions(H+ and NO3–) of HNO3 will be available in the aqueous solution that correspondingly shows its strong acid nature.
Also, the acid dissociation constant value(Ka) for HNO3 is 2.3 × 101.
⇒ If the value of the dissociation constant of acid is greater than 1 (Ka >> 1), then the nature of the compound is a strong acid.
⇒ If Ka << 1, then the nature of the compound is a weak acid.
Trick to remember the acidity strength of oxyacids
“An oxyacid is an acid that contains oxygen, hydrogen, and one other element(metal or non-metal)”. Examples of oxyacids:- H2SO4, HNO3, H3PO4, etc.
Trick– If oxyacids have 2 or more oxygen than hydrogen, then oxyacid is a stronger acid.
∴ HNO3 oxyacid has three oxygen and one hydrogen, so (3 -1 = 2), we have two oxygen left, Hence, it is a strong acid as per rule.
∴ H2SO4 oxyacids have four oxygen and two hydrogens, so (4 – 2 = 2), we have two oxygen left, hence, it is a strong acid.
∴ H3PO4 oxyacid has four oxygen and three hydrogens, so (4 – 3 = 1), we have only one oxygen left, hence, it is a weak oxyacid.
Here’s the list of some common strong or weak acids.
Is HNO3 also act as base?
When HNO3 faces or reacts with superior to it, then in this condition it acts as a base. What does it mean? It simply means, when HNO3 reacts with the less reactive element that accepts the proton, it will act as an acid.
And when HNO3 reacts with a more reactive compound like sulfuric acid or super acids that must donate the proton, it will act as a base. Does it make sense?
Let’s more elaborate on it, to understand in which condition HNO3 acts like acid and in which base.
HNO3 acts as an acid:
Just remember these two conditions to understand when HNO3 acts as an acid. Let’s take an example to crystal clear your doubt.
Here, HNO3 is acting as an acid because it donates the proton to H2O and forms the conjugate base.
H2O is very less reactive and very less acidic than HNO3, so, it has to accept the proton from a strong acid like HNO3.
HNO3 acts as a base:
Example – Sulfuric acid is more reactive and more acidic than HNO3. So, when reacting with sulfuric acid, HNO3 accepts the proton from it and forms the conjugate acid.
As H2SO4 is more acidic, it must donate the proton to HNO3 to gain stability, hence, it formed HSO4– conjugate base. Whereas, HNO3 has to accept the proton as H2SO4 is superior to it, hence, forming NO2+ conjugate acid.
⇒ H2SO4 + HNO3 → H2NO3+ + HSO4–
∴ H2SO4 + HNO3 → NO2+ + H2O + HSO4–
Therefore, in this case, HNO3 acts as a base since it accepts the proton from H2SO4.
Is HNO3 lewis acid or base?
In short, HNO3 acts as Lewis acid Because as per Lewis’s theory for acid, a compound that accepts the electron pair from another compound is classified as Lewis acid since HNO3 has an H+ ion that can accept the electron pairs from a compound donor.
⇒ Lewis acid → electron pair acceptor
⇒ Lewis base → electron pair donator
Note: Lewis acid is a superset of Bronsted-Lowry acids which means every compound that falls into the category of Bronsted-Lowry acid is Lewis acid.
As we already discussed, HNO3 is Bronsted-Lowry acid because it donates the proton when reacts with less acidic compounds than it such as H2O and forms the conjugate base. Therefore, HNO3 also acts as lewis acid.
Technically, HNO3 acts as lewis acid. Because the nitrogen central atom has a deficiency of electrons and it can accept the electron pair from another compound in order to release the proton from it.
And we know anything that accepts the electron pair from other compounds is Lewis acid in nature.
What is the Conjugate acid and base of HNO3
Conjugate acid is formed when one H+ has been added to the parent base and the conjugate base is formed when one proton or H+ ion is removed from the parent acid.
The concept of conjugate acid-base pair.
As we know, HNO3 sometimes acts as the base and sometimes as an acid. So, obviously, its conjugate acid-base pair also vary with its nature.
So, when the HNO3 acts as acid its conjugate base is NO3– and when it acts as the base then its conjugate acid is NO2+.
Is HNO3 stronger acid than HNO2?
Yes, HNO3 is a stronger acid than HNO2, one reason is that HNO2 does not dissociate completely in an aqueous solution to liberate proton or H+ ions whereas HNO3 is nearly 100% ionized in an aqueous solution and completely dissociates into H+ and NO3– ions.
Or check the conjugate base of acids to know the stability of the compound. Here, the HNO3 conjugate base is NO3– which is more stable than the conjugate base of HNO2 which is NO2–.
Because in the case of NO3–, the electron can delocalize over three oxygen but in the case of NO2–, the electron can delocalize over only two oxygen.
So, NO3– electron has a greater volume to stabilize the charge than the NO2–. Therefore, NO3– is more stable than NO2–.
Note: If the conjugate base of A acid is more stable than the conjugate base of B acid, then A is a stronger acid than B acid.
Uses of Nitric acid
Here comes the last part! It’s time to rewind this article on HNO3 acid or base with some highlighted or important points.
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What is the base of HNO3?
Answer: HNO3 is a strong acid, a base, a nitrator, and occasionally a heavy oxidizer. It acts as a base when there is a stronger acid present. Nitric acid is a stronger acid than nitrous acid because the conjugate base is more stable.
What type of acid or base is HNO3?
Nitric acid is a nitrogen oxoacid of formula HNO3 in which the nitrogen atom is bonded to a hydroxy group and by equivalent bonds to the remaining two oxygen atoms. It has a role as a protic solvent and a reagent. It is a conjugate acid of a nitrate.
Is HNO3 a strong or weak acid or base?
This means that it essentially fully ionizes when dissolved in water. Strong acids by definition fully ionize, therefore HNO3 H N O 3 is a strong acid.
What is the conjugate base of HNO3 acid?
Therefore, the conjugate base of nitric acid, HNO3, is the nitrate ion, which is symbolized as NO3–1.