Explain the order of increasing acid strength for the...

Explain the order of increasing acid strength for the following groups of acids and the order of increasing base strength for their conjugate bases. (a) $\mathrm{H}_{2} \mathrm{SO}_{3}, \mathrm{H}_{2} \mathrm{SO}_{4}$; (b) $\mathrm{HNO}_{2}, \mathrm{HNO}_{3} ;$ (c) $\mathrm{H}_{3} \mathrm{PO}_{3}, \mathrm{H}_{3} \mathrm{PO}_{4}$ (d) $\mathrm{HClO}, \mathrm{HClO}_{2}$ $\mathrm{HClO}_{3}, \mathrm{HClO}_{4}$

Explain the order of increasing acid strength for the following groups of acids and the order of increasing base strength for their conjugate bases. (a) $\mathrm{H}_{2} \mathrm{SO}_{3}, \mathrm{H}_{2} \mathrm{SO}_{4}$;
(b) $\mathrm{HNO}_{2}, \mathrm{HNO}_{3} ;$
(c) $\mathrm{H}_{3} \mathrm{PO}_{3}, \mathrm{H}_{3} \mathrm{PO}_{4}$
(d) $\mathrm{HClO}, \mathrm{HClO}_{2}$
$\mathrm{HClO}_{3}, \mathrm{HClO}_{4}$

Key Concepts

Acid Strength

Acid strength refers to an acid's ability to donate protons (H? ions) to a base. It is largely determined by the stability of the conjugate base that forms after deprotonation. The more stabilized the conjugate base—through factors like resonance, inductive effects, or electronegativity of neighboring atoms—the stronger the acid. In comparing different acids, structural factors such as the number and arrangement of oxygen atoms often play a critical role.

Conjugate Base Stability

The conjugate base's stability is crucial in determining the parent acid's strength. A more stable conjugate base, where the negative charge is effectively delocalized or stabilized by electron-withdrawing groups, corresponds to a stronger acid. The inverse relationship exists where a strong acid will produce a weak conjugate base, and vice versa, which is fundamental in analyzing acid-base equilibria.

Oxyacid Structure and Electronegativity

Oxyacids are acids that contain oxygen, hydrogen, and another central atom, and their acid strength is influenced by the electronegativity and oxidation state of the central atom. A higher oxidation state or more electronegative central atom in an oxyacid generally results in stronger acid behavior because it increases the electron-withdrawing effect on the OH bond, thereby facilitating proton donation.

Inductive and Resonance Effects

Inductive effects involve the transmission of charge through sigma bonds due to the electronegativity of atoms, which can stabilize negative charges in conjugate bases. Resonance effects allow the delocalization of electrons across multiple atoms, further stabilizing the negative charge that results from deprotonation. Both effects are key in explaining variations in acid strength among similar compounds.

Transcript

00:01 In this question, we have to explain the order of increasing acid strength for the given groups of acids.

00:09 And we have to explain the order of increasing base strength for their conjugate base.

00:15 The first group is h2 -s -o -3 sulfurous acid and sulfuric acid.

00:25 In both acids, sulfur is the central atom.

00:29 But sulfuric acid has one extra oxygen atom and which makes the oh -bone in sulfuric acid weaker.

00:42 So, sulfuric acid becomes stronger acid compared to sulfurous acid.

00:49 So we can write h2 -so -3 strength of h -2 -s -o -3 is less than the strength of sulfuric acid.

00:58 Now, stronger the acid, weaker is its conjugate base.

01:04 Therefore, the base strength of conjugate base of h2 -s -o -4 is h -s -4 -1 -is is weaker than h -s -o -3 -3 -h -s -3 -h -s -3 minus.

01:17 H -s -o -3 minus is the conjugate base of h -2 -s -3.

01:23 Now, for the next group, nitrous acid and nitric acid.

01:33 Both acid contain the same nitrogen as central atom in nitric acid as one extra oxygen atom which makes the oh bond weaker as compared to nitrous acid.

01:47 So nitric acid is stronger than nitrous acid.

01:52 So we can write acid strength of hno2 is less than the acid strength of nitric acid.

02:00 Now, stronger the acid, weaker is its conjugate base.

02:05 So, no3 minus is weaker base than no2 minus.

02:13 So basic strength of no3 minus is less than the basic strength of no2 minus.

02:20 No3 minus is the conjugate base of nitric acid, no2 minus is the conjugate base of nitrous acid.

02:28 Now for the next pair, phosphorus acid h3, po3, and phosphoric acid, h3, po4.

02:40 Here, both compound, both acid, has same central atom, phosphorus and phosphorus, and phosphoric acid has one extra oxygen which makes the oh bond weaker as compared to the oh bond in phosphoric acid.

03:02 So phosphorus acid h3po4 is stronger acid than phosphorus acid acid h3po3...

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