Page 179 - ICSE Chemistry 8
P. 179

Take a Break!

                     Write true (T) or false (F).
                      1.  Dissolu  on of salt can be physical or chemical depending upon the salt or compound
                          taken with water.                                                                     _______
                      2.  Dissolving a covalent compound like glucose results in a chemical change.             _______

                      3.  Water or any other liquid in which solute dissolves is called solvent.                _______
                      4.  A solu  on in which no more solute can be dissolved at a specifi c temperature is called
                          unsaturated solu  on.                                                                 _______

                      5.  The rate of forma  on of a solu  on increases with s  rring, hea  ng and addi  on of
                          small-sized par  cles of a solute.                                                    _______


                 TRUE SOLUTION, SUSPENSION AND COLLOID


                 We classify solu  ons into three types on the basis of the size of the solute present in them.
                     • True solu  on
                     • Suspension

                     • Colloid

                 True Solution

                 A true solu  on is a solu  on in which the solute size is comparable to molecular size less than 10 Angstrom.
                 It is a clear, transparent and homogeneous solu  on. Dis  lla  on is used to separate the solute from the
                 solvent. Sugar mixed with water and saline water are some examples of a true solu  on.
                 Suspension

                 A suspension is a cloudy but heterogeneous solu  on which consists of solid par  cles having par  cle size
                 above 10,000 Angstrom. The par  cles are heavy and therefore se  le down. The par  cles can be separated
                 by using the fi ltra  on technique. Oil in water and mud in water are some examples of suspension.

                 Colloid

                 A colloid is an opaque but homogeneous solu  on in which the solute size is between 10 to 1000 Angstrom.
                 A colloidal solu  on comes in between a true solu  on and a suspension. Smoke, fog, milk, cloud, paint,
                 moisturiser and emulsion are some examples of colloids. Colloids can be easily dis  nguished from other
                 solu  ons by the Tyndall eff ect.

                 Tyndall Effect

                 The par  cles of a colloid show Tyndall eff ect.

                 Tyndall eff ect can be explained as the sca  ering of light when a light beam passes through a colloid.
                 When a light beam falls on a colloidal solu  on, the par  cles sca  er and refl ect thus making the light beam
                 visible. Due to this phenomenon, the substance appears opaque. Tyndall eff ect makes it diffi  cult to see
                 through smoke or fog.


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