Acidic Strength and Factor Affecting it

Introduction

The acid’s ability to lose its H⁺ ion is measured by its acid strength. A strong acid’s dissociation in solution is nearly complete, with the exception of its most concentrated solutions. Some  Examples of strong acids are nitric acid, hydrochloric acid, perchloric acid, and sulfuric acid. In presence of both It’s dissociation product and  undissociated acid in the solution, a weak acid partially dissociates. Take, for instance, acetic acid. The effect of the substituents determine the strength of a weak organic acid. The oxidation state of the atom to which the proton may connect also affects the strength of an inorganic acid. It should be known that the acid strength is affected by solvent. For example, hydrogen chloride (HCl) is a strong acid in aqueous solution, but it is a weak acid when dissolved in glacial acetic acid.

Factors that determine Acidic Strength

• Periodic trends

First, we’ll look at individual atoms and consider trends related to an element’s location on the periodic table. As we proceed from carbon to nitrogen to oxygen along the second row of the periodic table, we can detect a distinct trend in acidity. The key to understanding this tendency is to analyse the hypothetical conjugate base in each case: the stronger the acid, the more stable (weaker) the conjugate base. Examine where the negative charge in each conjugate base finishes up. The negative charge in the ethyl anion is carried by carbon, but the charges in the methylamine anion and methoxide anion are carried by nitrogen and oxygen, respectively.

• The resonance effect

The differences in acidity and basicity across groups where the exchangeable proton was coupled to different elements were the focus of our research in the preceding section. Now it’s time to consider how the structure of distinct organic groups influences their relative acidity or basicity, even when the proton donor/acceptor is the same element.

• The inductive effect

The presence of chlorines obviously raises the acidity of the carboxylic acid group, but the argument isn’t because of resonance delocalization because the chlorinated molecules have no new resonance contributors. The inductive effect, on the other hand, provides the explanation for this phenomena. Because a chlorine atom has a higher electronegativity value than a hydrogen atom, it can ‘induce’ or ‘pull’ electron density away from the carboxylate group. In fact, the chlorine atoms aid in spreading out the electron density of the conjugate base, which has a stabilising effect as we all know. The chlorine substituent is referred to as an electron-withdrawing group in this context.

Factors affecting Acidic Strength

• The strength of the acid is determined by the strength of the H and A bonds. The lower the strength of the bond , the less energy is required to break it. As a result, the acid is potent.
• The strength of the H and A connection is affected by its polarity. The proton tends to exit the molecule easily if the link between them is extremely polar, making it a strong acid.
• If we use the aforementioned two parameters to compare acid strengths of elements in the same group of the periodic table, the bond strength becomes crucial.
• The polarity of the H and A bonds takes precedence when comparing the acid strengths of elements in the same row.
• The acid strength is influenced by the atomic size of A. The connection becomes weaker as the atom grows larger. As a result, there is a rise in the strength of acid.
• Through the inductive effect, inorganic carboxylic acids with an electronegative substituent can easily suck electron density out of an acidic bond. As a result, the pKa value is reduced.

Strong acid

A strong acid is one that dissociates when dissolved in solvent.

Weak acid

When dissolved in a solvent a weak acid is a substance that partially dissociates.

Acid Strength Order

It should be noted that when comparing elements in the same group of the periodic table, the strength of the H-A bond is a more essential component in determining acidity than its polarity. As the size of A diminishes as a group descends, the H-A bond strength falls, and the acid strength rises. Acid strengths of hydrides of elements belonging to  group-17 , is the example, rise in sequence.

HF < HCl < HBr < HI

Correct order of acidic Strength

1. The stronger the acid, the weaker is the conjugate base. As a result, any of the factors that stabilises the conjugate base raises acidity.

• species which loses H+ is the acid
• species which gains H+ is the base
• The factor that stabilizes the conjugate base will increase the acidity.
• The factor that destabilizes the conjugate base will decrease the acidity. 

1. The Atom’s “Polarizability” determines how well it can stabilise negative charge.
2. Negative Charge Is Stabilized by Electron Withdrawing Groups
3. Negative charge is stabilised by resonance because it is spread out across a larger area.
4. The higher the Hybrid Orbitals s-Character, the better. The More Consistent The Negative Potential

Conclusion

Chemical processes can be catalysed by strong acids. The pKa value of an acid determines how strong it is. Because the acid must be stronger in aqueous solution than a hydronium ion, its pKa must be lower. As a result, strong acids have a pKa value of <-174. Because strong acids can inflict severe chemical burns, they must be handled with caution. Some processes, such as the production and hydrolysis of carbonyl compounds, require strong acids to be catalysed. The concentration of hydronium ions in water is equal to the overall concentration (ionised and unionised) of the acid given to solution due to full dissociation of strong acids in aqueous solution. Certain processes can be accelerated by strong acids. Strong acids, for example, can speed up the formation and hydrolysis of carbonyl compounds.