Experiment of aim: To calculate the …

To determine the percentage of water absorbed by raisins.

Apparatus and materials required:

A bowl, forceps, a common balance, a weight box, blotting paper and a few raisins.

Theory:

When raisins are placed in water (a hypotonic solution), they absorb water by a process called osmosis and swell up. Osmosis is the net movement of solvent molecules from a region of their higher concentration to a region of their lower concentration through a semipermeable membrane. The movement of water into the cells of the raisins through their cell membranes continues until the cells become turgid.

This process is called endosmosis. If these swollen raisins are now kept in a concentrated salt or sugar solution (a hypertonic solution), water from the turgid raisins will come out of the cells and they will shrink. This process is called exosmosis.

The percentage of water absorbed by the raisins due to endosmosis can be measured by knowing the difference of their initial weight and final weight.

Procedure:

1. Take three raisins and weigh them on the common balance. Let this value be W₁.

2. Keep these raisins in a bowl containing water for 2 hours.

3. Take the raisins out of water and gently dry them with the help of blotting paper.

4. Weigh the soaked swollen raisins again on the common balance. Let this value be W₂.

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Observations:

1. Weight of dry raisins = W₁.

2. Weight of swollen raisins =W₂.

3. Weight of the water absorbed by raisins = W₂ – W₁.

4. Percentage (%) of water absorbed by raisins = W₂ – W₁/W₁× 100.

Result:

The soaked swollen raisins weigh more than the dry raisins. This is because the raisins absorbed water by the process of endosmosis.

Precautions:
1. The raisins should be weighed accurately.

2. The raisins should be immersed completely in water.

3. Before weighing the soaked raisins, these should be dried gently with the help of blotting paper.

Aim

To determine the mass percentage of water absorbed by raisins.

Theory
Dry raisins when soaked in water they absorb water and increases their size by the process of osmosis and swell up. Osmosis is the movement of solvent from higher concentration to lower concentration through semi-permeable membrane. The difference in mass between the swollen and dry raisins gives the amount of water absorbed by the raisins.

Materials Required
Raisins, Electronic balance, Blotting Paper, Bowl, Petridish and Forceps

Procedure
Step 1: 10 dry raisins is taken and weigh them on electronic balance. Let it be x.
Step 2: These raisins were put in bowl containing water for 2 hours.

Step 3: These raisins were taken out using forceps and dried gently with the help of blotting paper.
Step 4: Weigh these soaked raisins on electronic balance. Let it be y.

Observation
The weight of dry raisins is x grams and weigh of soaked raisins is y.

Calculation
Weight of water absorbed by raisins = (y - x)
Percentage of water absorbed by raisins = {(y - x)/x} × 100

Result
The weight of the raisins soaked in water is more than the dried raisins because raisins absorbed water by the process of endosmosis.

Precaution
1. Raisins should be dried and weigh accurately.
2. Raisins should be properly soaked.
3. Excess water should be dried gently before weighing.