Question

Write any four properties of a colloid.

Answer 1

1)colloid pass through filter paper .
2) it is a heterogeneous mixture.
3) show Tyndall effect
4) in colloidal solution , solute particles spread throughout liquid phase. they neither settle down nor dissolve.

Answer 2

What is Properties Of Colloids?

PROPERTIES OF COLLOIDALS

The main characteristic properties of colloidal solutions are as follows.

(1) Physical properties

(i) Heterogeneous nature : Colloidal sols are heterogeneousin nature. They consists of two phases; the dispersed phase and the dispersion medium.

(ii) Stable nature : The colloidal solutions are quite stable. Their particles are in a state of motion and do not settle down at the bottom of the container.

(iii) Filterability : Colloidal particles are readily passed through the ordinary filter papers. However they can be retained by special filters known as ultrafilters (parchment paper).

(2) Colligative properties

(i) Due to formation of associated molecules, observed values of colligative properties like relative decrease in vapour pressure, elevation in boiling point, depression in freezing point, osmotic pressure are smaller than expected.

(ii) For a given colloidal sol the number of particles will be very small as compared to the true solution.

(3) Mechanical properties

(i) Brownian movement

(a) Robert Brown, a botanist discovered in 1827that the pollen grains suspended in water do not remain at rest but move about continuously and randomly in all directions.

(b) Later on, it was observed that the colloidal particles are moving at random in a zig – zag motion. This type of motion is called Brownian movement.

(c) The molecules of the dispersion medium are constantly colloiding with the particles of the dispersed phase. It was stated by Wiener in 1863that the impacts of the dispersion medium particles are unequal, thus causing a zig-zag motion of the dispersed phase particles.

(d) The Brownian movement explains the force of gravity acting on colloidal particles. This helps in providing stability to colloidal sols by not allowing them to settle down.

(ii) Diffusion : The sol particles diffuse from higher concentration to lower concentration region. However, due to bigger size, they diffuse at a lesser speed.

(iii) Sedimentation : The colloidal particles settle down under the influence of gravity at a very slow rate. This phenomenon is used for determining the molecular mass of the macromolecules.

(4) Optical properties : Tyndall effect

(i) When light passes through a sol, its path becomes visible because of scattering of light by particles. It is called Tyndall effect. This phenomenon was studied for the first time by Tyndall. The illuminated path of the beam is called Tyndall cone.

(ii) The intensity of the scattered light depends on the difference between the refractive indices of the dispersed phase and the dispersion medium.

(iii) In lyophobic colloids, the difference is appreciable and, therefore, the Tyndall effect is well - defined. But in lyophilic sols, the difference is very small and the Tyndall effect is very weak.

(iv) The Tyndall effect confirms the heterogeneous nature of the colloidal solution.

(v) The Tyndall effect has also been observed by an instrument called ultra – microscope.