Question

While performing an experiment with raisins, a student recorded the following data.
Mass of water taken in the beaker=50g
Mass of raisins before soaking=20g
Mass of raisins after soaking=30g
Mass of water in the beaker left after experiment=40g
The % of water absorbed by the raisins is:
A) ${(50-40)g/40g×100}$
B) ${(50-40)g/50g×100}$
C) ${(30-20)g/30g×100}$
D) ${(30-20)g/20g×100}$

Answer 1

Raisins are the dried form of grape that swell up after absorbing the water because raisins consist of a higher concentration of solute. The percentage of water absorbed by raisins depends on the initial or final weight of water.

Complete answer:
The initial amount of water is 50g
Amount of water left after absorption is 40g
The percentage of water absorbed by the raisins is equal to the initial weight of water- final weight of water/ initial weight of water×100
= ${(50-40)g/50g×100}$ = 20%
Therefore 20% of water absorbed by the raisin in the given experiment.

Raisin is the dried form of grape so it has a high concentration of solute. In presence of solution, it shows endosmosis which is a type of osmosis where the movement of water and solvent molecules takes place from higher to lower concentration. Endosmosis swelling of the cell takes place whereas in exosmosis shrinkage of the cell takes place till the equilibrium is reached. Water potential becomes equal in both systems in case of equilibrium. If in case endosmosis and exosmosis both take place simultaneously in raisins then in presence of pure solution cell swell up which is known as deplasmolysis and in case of salt solution cell show plasmolysis because grape sap is less concentrated than the salt solution.

Hence, the correct answer is option (B).

Note: In the case of pickles, meat, fish, snacks, salting helps to kill the microbes by plasmolysis of their cell. Salt as a preservative results in osmotic shock in microbes which leads to loss of water from cells and retards the growth of cells resulting in death of microbes.