UPSC Combined Geo-Scientist, Mains · 2016 · Mains Paper II
Q1(h). Reverse osmosis
Question
Explain the term reverse osmosis.
Answer in brief
Reverse osmosis forces solvent from a solution towards the solvent side through a semipermeable membrane by applying pressure exceeding the osmotic-pressure difference.
Key points
- In ordinary osmosis, solvent moves from the dilute side to the more concentrated side because of the solvent chemical-potential difference.
- A membrane permeable mainly to solvent retains most dissolved solute. Applying excess pressure to the concentrated side reverses the solvent flux.
- For an ideal dilute solution, the osmotic pressure is approximately π=cRT (or icRT for a dissociating solute).
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.
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All parts of Question 1
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- 1(b) Inclined capillary5 marks
- 1(c) Entropy and diffraction5 marks
- 1(d) Equipartition in hydrogen5 marks
- 1(e) Expansion cooling of helium5 marks
- 1(f) Temperature dependence of equilibrium5 marks
- 1(g) Ammonium chloride pH5 marks
- 1(h) Reverse osmosis5 marks
- 1(i) Rate-law determination5 marks
- 1(j) Monolayer surface area5 marks
- 1(k) Electrolysis of copper sulfate5 marks
- 1(l) Ionization of helium ion5 marks
- 1(m) Photochemical quantum yield5 marks
- 1(n) Momentum in a box5 marks
- 1(o) Formaldehyde electronic transitions5 marks
- 1(p) NMR distinction of ethers5 marks