Colloids or Colloidal Solutions

A colloid has properties that are intermediate between those of a true solution and a suspension. Colloids have particles that are larger than the particles of a true solution but are smaller than those of a suspension. Between these extremes dispersed particles that are large than molecules, but not so large that the components of the mixture separate under the influence of gravity. These intermediate types of dispersions are called colloidal dispersion, or simply colloids. Colloids form the dividing line between solution and heterogeneous mixtures.

Examples :-

Colloids or colloidal solutions are milk, ink, blood, toothpaste, starch solution, air (containing dust), clouds, mist (dispersion of water droplets in air), smoke and jellies. A colloid is usually translucent or opaque.

Properties of a colloidal solution :-

Heterogeneous nature : A colloidal solution is heterogeneous. The particles are visible under a powerful microscope.

Filtration : The particles in a colloid can pass through a filter paper.

Stability : The particles in a colloid are quite stable. They do not settle down at the bottom when the colloid is left undisturbed.

Size of particles : The most characteristic property of a colloidal particle is its size. Colloidal particles have sizes ranging from 10-7 cm to 10-5 cm.

Brownian movement : Colloidal particles are in a state of constant and rapid zigzag motion, called Brownian movement. Brownian movement arises due to the collisions of the colloidal particles with the particles of the solvent.

Tyndall effect :- All colloidal solutions are capable of scattering light or opalescence. When a beam of converging rays falls in colloidal solution, scattering of light by sol particles in all the directions, given rise to a bright glowing cone when looked at it sideways. This is known as Tyndall effect. The solution particles absorb light, become self luminous and then scatter light in all possible directions.

Sample Questions

(More Questions for each concept available in Login)

Question : 1

Which of the following statements is not true about the colloids?
A. Colloids are quite stable
B. The particles of all colloids can be seen with a microscope
C. A colloid appears homogenous
D. The particles of colloids can pass through a filter paper
Right Option : B
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Question : 2

A colloid is a _________________ mixture.
A. Heterogeneous	B. Homogenous	C. Both a and b	D. Pure
Right Option : A
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Question : 3

In a colloidal solution , _______________________________
A. the size of a colloidal particle lies roughly between 0.1 nm to 1 nm.
B. the particles have a tendency to settle when the solution is left standing.
C. the particles pass through ultrafilter papers and animals and vegetable membranes.
D. the dispearsed phase is uniformly distributed in the dispersion medium
Right Option : D
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