Question

One of the strongest superacids known is the mixture of hydrogen fluoride and antimony pentafluoride. Write a chemical reaction for the formation of the solvated proton like that on the last slide of the acid-base lecture. Assume HF is the solvent. Describe in what ways, if any, the formation of this superacid illustrates each of the acid-base concepts discussed in class.

Answer 1

Super Acid:- There are two definition of super acid which are popular

1. A superacid is an acid with an acidity greater than that of 100% pure sulfuric acid.

2.A superacid is a medium in which the chemical potential of the proton is higher than in pure sulfuric acid.

Examples of super acid:-

1. Fluoroantimonic acid (HSbF6)

2. Trifluoromethanesulfonic acid (CF3SO3H)

3.Fluorosulfuric acid (HSO3F)

In your problem you have mentioed fluoroantimonic acid so we will discuss this acid only

Fluoroantimonic acid (HSbF6),:-

Fluoroantimonic acid(HSbF6) the strongest known superacid, is made by combining HF with SbF5..Various mixtures produce the superacid, but mixing equal ratios of the two acids produces the strongest superacid known to man. It can be as much as 2 × 1019 times stronger than 100% H2SO4.

chemical reaction:-

HF + SbF5 → H+ SbF6-

  In HSbF6 hydrogen ion (H+) attaches to the fluorine via a very weak dipolar bond. The weak bond accounts for the extreme acidity of fluoroantimonic acid, allowing the proton to jump between anion clusters.

Key Features of  Fluoroantimonic acid:-

• It is formed by  combination of a strong Lewis acid(SbF5) and a strong Brønsted acid(HF)
• HSbF6  is an ionic compoud and strongest bronsted lowry acid
• Explosively decomposes upon contact with water. Thats why fluoroantimonic acid cannot be used in aqueous solution. It is only used with hydrofluoric acid as a solvent.
• Protonates almost all organic compounds
• Dissolves glass and many other materials

In last part your problem wants to relate acid base theories with this acid HSbF6 So popularly it is termed as bronsted lowry acid because it can donate proton in any medium and it can also be termed as a arrhenius acid because it gives H+ ion in  aqueous solution but it is not used in aqueous solution because reaction is explosive. and HSbF6 is formed by HF which acts as a lewis base and SbF5 which acts as a lewis acid.