question_answer 41)

  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) A 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) Fine beam of light entering through a small  hole in a dark room. Illuminates the particles in its paths.

Answer:

  (a) The process is sublimation because when dry ice (solid CO2) is kept at room temperature at one atmospheric pressure, it sublimes leaving no residue. (b) This process is diffusion because in diffusion, mixing of one substance (ink) into another substance (water) goes on until a uniform mixture is formed. (c) This process is dissolution/diffusion as potassium permanganate crystal is dissolved in water. (d) This process is evaporation as acetone evaporates when kept open in the bottle. (e) This process is centrifugation. Milk is put in a closed container in big centrifuge machine. When machine is switched on, milk is rotated at a very high speed. Due to this, milk separates into 'cream' and 'skimmed milk'. The cream being lighter, floats over the skimmed milk and then can be removed. (f) This process is sedimentation as sand does not dissolve completely in water and forms suspension and settles down at the bottom when left undisturbed for some time. (g) This shows Tyndall effect, i.e., scattering of light by colloidal solution or by particles in a fine suspension. Dust particles are suspended in air which scatter the light coming from small hole.