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Chemistry · 2025 · 3 marks
CBSE 2025 · Region 5 · Set 1 · Q22
(a) Shweta mixed two liquids A and B of 10 mL each. After mixing, the volume of the solution was found to be 20 · 2 mL. (i) Why was there a volume…
(a)
Shweta mixed two liquids A and B of $\displaystyle 10$ mL each. After mixing, the volume of the solution was found to be $\displaystyle 20 \cdot 2 \mathrm{~mL}$.
(i)
Why was there a volume change after mixing the liquids ?
(ii)
Will there be an increase or decrease of temperature after mixing ?
(iii)
Give one example for this type of solution.
OR
(b)(i)
How does sprinkling of salt help in clearing the snow covered roads in hilly areas ?
(ii)
What happens when red blood cells are kept in $\displaystyle 0 \cdot 5 \%$ (mass/vol) NaCl solution ? Justify your answer.
(iii)
Write an application of reverse osmosis.
Marking-scheme solution
(a)(i)
The solution is non ideal, shows positive deviation from Raoult’s law / A-B interactions are
weaker than A-A and B-B interactions
(ii)
Decrease in temperature
(iii)
Ethanol and acetone
(b)(i)
Salt lowers the freezing point of water and prevents formation of ice and hence its easy to
clean.
(ii)
-Red blood cells swell up
-As the solution is hypotonic, water will flow into the cell/ As the solution is hypotonic,
endosmosis occurs.
(iii)
Desalination of sea water
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CBSE Class 12 Chemistry past-paper question from the 2025 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.