CBSE 2025 · Region 2 · Set 1 · Q29 · 4 marks
The spontaneous flow of the solvent through a semipermeable membrane from a pure solvent to a solution or from a dilute solution to a concentrated solution is called osmosis. The phenomenon of osmosis can be demonstrated by taking two eggs of the same size. In an egg, the membrane below the shell and around the egg material is semipermeable. The outer hard shell can be removed by putting the egg in dilute hydrochloric acid. After removing the hard shell, one egg is placed in distilled water and the other in a saturated salt solution. After some time, the egg placed in distilled water swells-up while the egg placed in salt solution shrinks. The external pressure applied to stop the osmosis is termed as osmotic pressure (a colligative property). Reverse osmosis takes place when the applied external pressure becomes larger than the osmotic pressure.(a)Define reverse osmosis. Name one SPM which can be used in the process of reverse osmosis.(b)What do you expect to happen when red blood corpuscles (RBC's) are placed in $\displaystyle 0.5 \% \mathrm{NaCl}$ solution ?(ii)Which one of the following will have higher osmotic pressure in $\displaystyle 1$ M KCl or $\displaystyle 1$ M urea solution. Justify your answer.(c)Why osmotic pressure is a colligative property ?
The spontaneous flow of the solvent through a semipermeable membrane from a pure solvent to a solution or from a dilute solution to a concentrated solution is called osmosis. The phenomenon of osmosis can be demonstrated by taking two eggs of the same size. In an egg, the membrane below the shell and around the egg material is semipermeable. The outer hard shell can be removed by putting the egg in dilute hydrochloric acid. After removing the hard shell, one egg is placed in distilled water and the other in a saturated salt solution. After some time, the egg placed in distilled water swells-up while the egg placed in salt solution shrinks. The external pressure applied to stop the osmosis is termed as osmotic pressure (a colligative property). Reverse osmosis takes place when the applied external pressure becomes larger than the osmotic pressure.
(a)
Define reverse osmosis. Name one SPM which can be used in the process of reverse osmosis.
(b)
What do you expect to happen when red blood corpuscles (RBC's) are placed in $\displaystyle 0.5 \% \mathrm{NaCl}$ solution ?
(ii)
Which one of the following will have higher osmotic pressure in $\displaystyle 1$ M KCl or $\displaystyle 1$ M urea solution. Justify your answer.
(c)
Why osmotic pressure is a colligative property ?
Marking-scheme solution
(a)
•
When external pressure is larger than the osmotic pressure, then the movement of
solvent is from solution to solvent side through semi permeable membrane. / The
direction of osmosis can be reversed if a pressure larger than the osmotic pressure is
applied to the solution side.
•
Cellulose acetate.
(i)
RBC swells up / Cells swell and may even burst due to endo-osmosis.
(ii)
$\displaystyle 1$ M KCl,
i = $\displaystyle 2$ / KCl dissociates into ions, whereas urea does not dissociate.
(c)
It depends upon the number of solute particles in the solution.
SolutionsColligative Properties and Determination of Molar MassUnderstandcase_studymedium
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CBSE Class 12 Chemistry past-paper question from the 2025board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.