To prepare a colloidal solution of starch in water and egg albumin/milk in water- Class 9th Science Lab Work
Aim
To prepare a colloidal solution of starch in water and egg albumin/milk in water and distinguish between these on the basis of:
(i) transparency
(ii) filtration criterion
(ii) filtration criterion
(iii) stability
Theory
In colloidal solution, the size of particles are smaller than 10-5 cm or smaller (generally 10-5 or 10-7). It is heterogeneous in nature and particles of one substance dispersed through another substance. It has dispersed medium and dispersed phase.
Materials Required
Beakers, Test tubes, Starch, Egg albumin/milk, Glass Rod, Water
Procedure
For colloidal solution of starch in water:
Step 1: 1% of dry corn starch is mixed with 3 ml of distilled water in beaker.
Step 1: 1% of dry corn starch is mixed with 3 ml of distilled water in beaker.
Step 2: 97 ml of boiling distilled water is added to it and stirred well.
Step 3: It is been heated for 2 minutes and stored in test tube labelled A after cooling.
For colloidal solution of egg albumin/milk
Step 1: 1g of egg albumin/milk (the colourless fluid found around the yellow yolk) and 5 ml of distilled water is taken in beaker and mixed it well.
Step 2: 5 ml of distilled water is slowly added while stirring continuously.
Step 3: Few drops of acid (dil.HCl/dil.H2SO4 or acetic acid) is added to it after mixing.
Step 4: The clear solution of albumin and water became turbid which is stored in test tube labelled B.
For colloidal solution of egg albumin/milk
Step 1: 1g of egg albumin/milk (the colourless fluid found around the yellow yolk) and 5 ml of distilled water is taken in beaker and mixed it well.
Step 2: 5 ml of distilled water is slowly added while stirring continuously.
Step 3: Few drops of acid (dil.HCl/dil.H2SO4 or acetic acid) is added to it after mixing.
Step 4: The clear solution of albumin and water became turbid which is stored in test tube labelled B.
Observation Table
| Property | Experimental Procedure | Observation | Inference |
| Transparency | Small strip of cellophane paper is pasted on each test tubes and the coloured paper of each test tube is observed from other side of test tube. | Coloured spot appears dim from the other side of test tubes A and B. | A colloid is translucent. |
| Filtrate | Contents of test tubes labelled as A and B are filtrated. | Filtrate obtained is translucent. No residue left on the filter paper in both the cases. | Components causing colloid cannot be separated by filtration. |
| Stability | Leave the test tubes without disturbance for 20-25 minutes. | No change is observed in test tubes A and B. | Colloids are stable and solute particles do not settle down when left undisturbed. |
Results and Discussion
Colloidal solutions are translucent and their particles can pass through filter paper to give translucent filtrate. No residue particles are left as residue on the filter paper.
Precautions
(i) Handle the materials and solutions with care.
(ii) While filtering a solution drop the contents along a glass rod into the beaker.
(iii) Keep the sample undisturbed while checking stability.
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