UPSC Combined Geo-Scientist, Mains · 2018 · Mains Paper I
Q1(d). Bronsted and Lewis acids
Question
All Bronsted-Lowry acids are Lewis acids also. But all Lewis acids are not Bronsted-Lowry acids. Explain.
Answer in brief
A Brø nsted acid supplies a proton that accepts an electron pair; a Lewis acid need not contain or transfer any proton.
Key points
- A Brø nsted–Lowry acid is a proton donor. During proton transfer, a base donates its lone pair to the acidic hydrogen, forming a new bond.
- For example, HCl + NH₃ → NH₄⁺ + Cl⁻; the nitrogen lone pair bonds to the transferred proton.
- BF₃ accepts the lone pair of NH₃ to form an adduct, yet it has no proton to donate.
The full model answer
As written for the answer booklet: the diagram carries the working, the lines stay short. Read here only; it is not offered as a download.
CoversBronstedLewis acidsAcid–base concepts
All parts of Question 1
- 1(a) Lithium hydride5 marks
- 1(b) Coordination nomenclature5 marks
- 1(c) Werner valencies and isomers5 marks
- 1(d) Bronsted and Lewis acids5 marks
- 1(e) Halogen displacement5 marks
- 1(f) Predicting carbonyl numbers5 marks
- 1(g) Radiocarbon age5 marks
- 1(h) Alkali-ion selectivity of resins5 marks
- 1(i) Borazine and benzene5 marks
- 1(j) Anomalous lanthanide radii5 marks