My teacher said that semipermeable membrane allows passage of only selected particles and then said that it is required for osmosis but I cannot totally understand the main function of semipermeable membrane in osmosis.
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$\begingroup$ When in doubts about statements of lectures or textbooks, always try first to verify the facts in independent available offline or online sources, before you decide to ask. CH SE should not be the 1st choice in looking for the authoritative answer. $\endgroup$– PoutnikCommented Apr 25, 2023 at 9:59
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$\begingroup$ If the membrane was not selective, it would allow passage of nothing or of all. Is any of these two cases osmosis? $\endgroup$– PoutnikCommented Apr 25, 2023 at 10:07
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$\begingroup$ There is some detail in this answer chemistry.stackexchange.com/questions/167189/… $\endgroup$– porphyrinCommented Apr 25, 2023 at 10:48
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$\begingroup$ @Poutnik I am preparing for an exam and I also have to deal with 3 other subjects also so I don't have much time for verification I know you are correct but please understand my situation also. $\endgroup$– Rohan SinghCommented Apr 25, 2023 at 12:35
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2$\begingroup$ You do not have time to verify but you have time to ask. But the former is faster. $\endgroup$– PoutnikCommented Apr 25, 2023 at 13:00
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1 Answer
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A semipermeable membrane is a membrane containing tiny holes. The dimension of the holes is just sufficient to let small molecules like water molecules ($\ce{H2O}$) go through the membrane. Big molecules like sugars or proteins are not small enough to go through the membrane. So if a semi-permeable membrane separates pure water on one side and a sugar solution on the other side, water goes through the holes and sugar does not. In the long range, more water is going through the membrane in the direction water -> solution than in the inverse movement. As a consequence, the aqueous solution gets slowly more and more diluted. This is osmosis.
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$\begingroup$ Thanks sir for such a clear explanation but can you tell me one more thing that, why π is directly the to molar concentration of solute (π = osmotic pressure) ? $\endgroup$ Commented Apr 25, 2023 at 12:39