Question

1g of polymer having molar mass 1,60,000g is dissolved in 800 ml water. Calculate the osmotic pressure in pascal at ${{27}^{0}}C$.
A.19.4
B.0.90
C.0.50
D.1.20

Answer 1

Hint: The concept of osmosis and osmotic pressure is to be used in this question. The above question can be solved by relating osmotic pressure to the number of moles of solute, by the Van't Hoff equation.

Complete answer:
In order to answer this question, we need to learn about osmosis and osmotic pressure. In 1748, Abbey Nollet was first to observe that when a semipermeable membrane (SPM) was placed between pure solvent and solution, the pure solvent started flowing through the SPM into the solution. Similarly, when two solutions of different concentrations were separated by the semi-permeable membrane, then the solvent flows from dilute solution (lower concentration) into solution of higher concentration. The passage of solvent from pure solvent or from solution of lower concentration into solution of higher concentration through the semipermeable membrane is called osmosis.
Different theories have been proposed to explain the phenomenon of osmosis but vapour pressure approach is the most accepted. According to this, osmosis occurs as a result of difference in the vapour pressures of solution and pure solvent (or between two solutions). The vapour of pure solution is lower than that of solvent. Therefore, vapours of solvent travel spontaneously from a region of higher to a place of lower vapour pressure. As a result, there is net transfer of solvent particles from pure solvent into solution (or from a solution of lower concentration to that of higher concentration). The osmotic pressure depends only upon the molar concentration of solute but does not depend upon its nature, for a given solvent. Osmotic pressure is related to the number of moles of the solute by the following relation:
\[\begin{align}
& \pi V=nRT \\
& or,\,\pi =\frac{n}{V}RT \\
& \Rightarrow \pi =CRT \\
\end{align}\]
Where C=concentration, R=gas constant, T=temperature=volume. Now, by substituting the data given in the question,we can write:
\[\begin{align}
& \pi =CRT \\
& \Rightarrow \pi =\frac{1}{1.6\times {{10}^{5}}}\times \frac{8.314\times 300}{800\times {{10}^{-6}}}=19.4Pa \\
\end{align}\]

So, we obtain option A as our correct answer.

NOTE: Some examples of osmosis include:
i.Shriveling of raw mangoes to pickel.
ii. Revival of wilted flowers and limped carrots.
iii. Swelling of tissues in people consuming more salt.
iv. Preservation of meat.
v. Absorption of water by plants.