Name the process associated with the following.
(a) Dry ice is kept at room temperature and at one atmospheric pressure.
(b) A drop of ink placed on the surface of water contained in a glass spreads throughout the water.
(c) A potassium permanganate crystal is in a beaker and water is poured into the beaker with stirring.
(d) An acetone bottle is left open and the bottle becomes empty.
(e) Milk is churned to separate cream from it.
(f) Settling of sand when a mixture of sand and water is left undisturbed for some time.
(g) A fine beam of light entering through a small hole in a dark room illuminates the particles in its paths.
(a) Sublimation.
When dry ice (solid CO2) is kept at room temperature at one atmospheric pressure, it sublimes (changes into vapours) leaving no residue behind.
(b) Diffusion.
When a drop of ink is placed on the surface of water contained in a glass, it spreads throughout the water. This process of mixing of one substance (ink) into another substance (water) takes place by the process of diffusion. This mixing goes on until a uniform mixture is formed.
(c) Dissolution/diffusion.
When a potassium permanganate crystal is kept in a beaker and water is poured into the beaker with stirring potassium permanganate crystal is dissolved in water the process of dissolution/diffusion.
(d) Evaporation, diffusion.
When an acetone bottle is left open, the bottle becomes empty. This happens because acetone evaporates when kept open in the bottle.
(e) Centrifugation.
Milk is churned to separate cream from it by the process of centrifugation. Milk is put in a centrifuge machine. Milk is rotated at a very high speed in the centrifuge machine. As a result, milk separates into ‘cream’ and ‘skimmed milk’. The cream being lighter floats over the skimmed milk and can be removed.
(f) Sedimentation.
Sand settles down when a mixture of sand and water is left undisturbed for some time by the process called sedimentation. This happens because sand is insoluble in water and forms a suspension. Thus, it settles down at the bottom when left undisturbed for some time.
(g) Scattering of light (Tyndall effect).
A fine beam of light entering through a small hole in a dark room illuminates the particles in its paths due to scattering of light (Tyndall effect) by particles in a fine suspension. Dust particles are suspended in air that scatters the light coming from the small hole.