explain the statement, “inorganic components make stronger acids than organic components”.

Question

Use your understanding of acid solutions, atomic bonding theory, polarity, discussion of intramolecular bonds and intermolecular forces to explain the statement, “inorganic components make stronger acids than organic components”.

Answer 1

Hi Bobby B.,

The assertion is mostly, but not completely, true!

It's true that ions such as (SO4)-2 and Cl-1 have the ability to attach (a) proton[s], somewhat loosely, because their internal structures (be they bonds or just electron shells) are strong, and that therefore the protonated species allow that proton to be released easily == a strong acid .

It's also true that organic species with a carboxylic acid (-CO2H) group have in general a much gentler tendency to let that proton go == weaker acids. (The oxygen that lets the H go isn't all that (-) charged, hence doesn't hold a (H+) so well.)

However, whatever else is nearby has a marked effect on how strong a carboxylic acid is. Thus:

parent acid: CH3COOH CFH2COOH CF2HCOOH CF3COOH

pKa in H2O: 4.7 2.66 1.24 0.23

That's about a factor of 30000 stronger acidity with the three flourines on the carbon next door!

And then there's paratolenesulfonic acid, pKa -2.8 and

Carborane acid H(CHB₁₁Cl₁₁) pKa < - 18

So vs. inorganic acids,:

1. Hydroiodic acid HI (pK_a = −9.3)
2. Hydrobromic acid HBr (pK_a = −8.7)
3. Perchloric acid HClO₄ (pK_a ≈ −8)
4. Hydrochloric acid HCl (pK_a = −6.3)
5. Sulfuric acid H₂SO₄ (first dissociation only, pK_a1 ≈ −3)

those inorganic acids look pretty pitiful!

Now let's look in the other direction on the pKa scale:

Within a period on the periodic table, the strength of a comparable neutral molecule as an acid varies drastically: pKa (CH₄) = 51, pKa (NH₃) = 38, pKa (H₂O) = 15.7, and pKa (HF) = 4.0. Thus, the ions formed by splitting H⁺ from each of these, namely CH₃^-, NH₂^-, OH^-, and F^- respectively, are very very very, very very, very, and somewhat unhappy to be without their proton.

Hope that gives you some ammo for discussing the question!

-- CHeers, --Mr. d.