question_answer

  (a) Action of heat on blue vitriol is a physical as well as chemical change. Justify. (b) How would you separate a mixture of NH4Cl and I2? (c) How can you prove that air is a mixture? Or Give an example each for the mixture having   following   characteristics. Suggest a suitable method to separate the components of these mixtures. (a) A volatile and non-volatile component. (b) Two volatile components with appreciable difference in boiling points. (c) Two immiscible liquids. (d) One of the components changes directly from solid to gaseous state. (e) Two   or   more   coloured constituents soluble in some solvent.

Answer:

  (a) When blue vitriol is a gradually heated to about 800°C, it undergoes a physical change to form a white powder. On adding a drop of water to the white powder, it changes back to blue. Thus, the change is a physical change. On strongly heating, copper sulphate (blue vitriol) decomposes to give new substances like copper oxide and sulphur dioxide. On cooling these, copper sulphate cannot be re-obtained. Thus, it is a chemical change.                                                                                                                                                               (b) Heating cannot separate the mixture, as both substances sublime on heating. However, when water is added to the mixture, dissolves but does not. The mixture is filtered. The filtrate is a solution of while the residue is iodine. The filtrate is heated to obtain crystals by evaporation or distillation. (c) (i) The composition of air is variable. The composition varies from place to place and with altitude. For instance, at higher altitudes, there is less oxygen in the air. In industrial areas, due to the waste gases coming out of industrial chimneys in the form of smoke, more impurities are added in the air. (ii) Air has no definite set of properties. Its properties are an average of its constituents. e.g., vapour density of oxygen is 16, vapour density of nitrogen is 14 and vapour density of air is 14.4. (iii) The components of air can be separated by physical means. Fractional distillation of liquid air can separate N2 and O2. Boiling point of a liquid Boiling point of a liquid (iv) The formation of air does not involve any energy change. No energy is released or absorbed when the constituents of air are mixed in the right proportion. (v) Air cannot be assigned a fixed chemical formula.                                                                                                        (2) Or (a) Mixture of acetone and water-simple distillation.                                                                                      (1/2)+(1/2) (b) Mixture of kerosene and petrol-simple distillation.                                                                                   (1/2)+(1/2) (c) Mixture of mustard oil and water-separating funnel (decantation).                                                   (1/2)+(1/2) (d) Mixture of ammonium chloride and common salt-sublimation.                                                           (1/2)+(1/2) (e) A mixture of different pigments from an extract of flower petals-chromatography.                                  (1/2)+(1/2)