Question

Preparation of
(a) True solution of common salt, sugar and alum
(b) A suspension of soil, chalk powder and fine sand in water
(c) 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
(iii) stability

Answer 1

A true solution is defined as the homogeneous mixture of two or more components. The size of the particle is between 10 to 9 nm. The example of a true solution is a simple sugar solution in water. A colloidal solution is a mixture in which one component is split into fine particles which get dispersed into a second substance.

Complete answer: (a) The true solution is homogeneous mixture which cannot be separated by the process of filtration. A true solution is said to be stable and transparent. Three beakers are taken in which 100mL water is added and are labelled as A,B,C. Then the addition of 10g powered salt, sugar and alum is added to each beaker. For transparency we will add a small strip of cellophane paper and paste then on each test tube and observe the colour. The colour spot is seen clearly, which means true solutions are transparent. For filtration all the contents in beakers are filtered and observing we see no residue is seen so solid particles are not able to separate from the true solution. For stability leave the test tube without disturbing it for 25 minutes, we see that no change has occurred. This means true solutions are stable.
(b) For the transparency, filtration and stability in colloidal solution we will take three beakers in which 100mL water is added and are labelled as A,B,C. Then the addition of 10g of fine sand, chalk powder and soil is added in each beaker. For transparency we will add a small strip of cellophane paper and paste then on each test tube and observe the colour. The colour spot is not seen clearly, which means colloidal solutions are not transparent. . For filtration all the contents in beakers are filtered and observing we see that the residue is seen so solid particles are able to separate from colloidal solutions. For stability leave the test tube without disturbing it for 25 minutes, we see that settlement of solid particles has occurred. This means colloidal solutions are not stable.
(c) For the colloidal solution of starch in water 1% of dry corn starch is mixed with 3mL of distilled water in the beaker. Then the addition of 97mL of boiling distilled water is added and stir it well. Then heat it for two minutes and store it in labeled test tube A after cooling.
For colloidal solution of egg albumin or milk 1g of milk or egg albumin and 5mL of distilled water is taken in beaker and mixed well. Then the addition of 5ml water is done on stirring. Few drops of dilute hydrochloric acid is added after mixing and then the mixture is stored in labeled test tube B. For transparency we will add a small strip of cellophane paper and paste then on each test tube and observe the colour. The colour spot is seen dim, which means the colloid is translucent. For filtration all the contents in beakers are filtered and observing we see that no residue is seen on the filter paper. So the colloid cannot be separated by filtration. For stability leave the test tube without disturbing it for 25 minutes, we see that no change of solid particle occurs. This means colloidal solutions are stable.

Note: The precautions one should take during such experiments are the materials and solutions should be handled with care. While filtering the components the contents should be dropped with a glass rod. One should not disturb the sample while checking stability.