UPSC Combined Geo-Scientist, Mains · 2019 · Mains Paper I
Q1(j). Diborane with excess ammonia
Question
Identify the product(s) in the following reaction: B₂H₆ + NH₃ (excess) →(low temperature).
Answer in brief
The conventional low-temperature product is diammoniate of diborane, [BH₂(NH₃)₂]⁺[BH₄]⁻.
Key points
- Write the stoichiometric formation as B₂H₆ + 2NH₃ → [BH₂(NH₃)₂]⁺ + BH₄⁻.
- The product is an ionic borohydride salt, not simply two ammonia molecules loosely attached to an unchanged diborane structure.
- The cation has B bonded to two H atoms and two ammonia N donors.
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.
CoversDiborane with excess ammoniaBoron hydrides
All parts of Question 1
- 1(a) Permanganate and iron(II)5 marks
- 1(b) Carbon isotopes and stability5 marks
- 1(c) Diagonal relationship5 marks
- 1(d) Conductivity of phosphoric acid5 marks
- 1(e) Oxidation of Fe(II) and Mn(II)5 marks
- 1(f) Melting points of bromine and iodine chloride5 marks
- 1(g) Small dipole moment of CO5 marks
- 1(h) Acidity of concentrated HF5 marks
- 1(i) Temperature and conductivity5 marks
- 1(j) Diborane with excess ammonia5 marks