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)
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