Do heterogeneous mixtures settle out by themselves?

• HETEROGENEOUS MIXTURES are those mixtures in which the
  two substances ( that can be pure substances ) do not mix with each other properly resulting in formation of boundaries .

• For example :

• Mixture of sand and water

• Mixture of oil and water

• Mixture of salt and sugar etc.

• As a good learner , you should perform the experiment by making all these mixtures in reality by yourself .Then only, you will realize that on making heterogeneous mixtures , it settle out by themselves without any shaking .

Heterogeneous mixtures are those that contain more than one separate phase, so either solids dispersed into liquids, or two immiscible liquids, or two or more powdered solids, for example.

Some of these will settle out by themeslves if left undisturbed, for example if you shake up a container of oil and water it will initially form a water/oil dispersion, but on standing the oil and water will settle out into two layers.

Similarly, if you stir up a mixture of powdered clay and water it forms a solid in water dispersion, but left standing the clay sediments out to form a separate layer at the bottom of the container.

However, some heterogeneous mixtures do not settle out by themselves. For instance colloidal dispersions. Examples include milk (water/fat dispersion, stablised by proteins), pigmented inks (pigment dispersed in ink solvent), certain types of emulsion pants. Colloidal dispersions do not spontaneously settle out due to the dispersed phase being stabilsed so that coagulation or coalescence is made unfavourable due to steric or electrostatic repulsion.