The acids which are stronger than pure sulfuric acid are called superacids. Superacids are very stro — Analytical Chemistry Chemistry Question
Superacids
The acids which are stronger than pure sulfuric acid are called superacids. Superacids are very strong proton donors being capable of protonating even weak Lewis acids such as Xe, H2, Cl2, Br2, and CO2. Cations, which never exist in other media, have been observed in superacid solutions. George Olah received the Nobel Prize in Chemistry in 1994 for the discovery of carbocation generation by using superacids. The enhanced acidity is due to the formation of a solvated proton. One of the most common superacids can be obtained by mixing SbF5 and HF. When liquid SbF5 is dissolved in liquid HF (in molar ratio of SbF5 / HF greater than 0.5) the SbF6 – and Sb2F11 – anions are formed, and the proton released is solvated by HF.
Write balanced chemical equations to show the species formed when HF and SbF5 are mixed.
Model Answer
2 HF + SbF5 → H2F+ + SbF6–
2 HF + 2 SbF5 → H2F+ + Sb2F11– or
4 HF + 3 SbF5 → 2 H2F+ + SbF6– + Sb2F11–
Draw the structures of SbF6– and Sb2F11– (in both ions the coordination number of antimony is 6 and in Sb2F11– there is a bridging fluorine atom).
Write the chemical equations for the protonation of H2 and CO2 in HF/SbF5 superacid solution.
Model Answer
H2F+ + H2 → HF + H3+
H2F+ + CO2 → HF + CO2H+ ( or HCO2+)
Draw the Lewis structure of HCO2+ including the resonance forms and estimate the H−O−C bond angle in each resonance form.
Model Answer
120 ° 109,5 ° 180 °