Is Matter Around Us Pure
Q56. How are heterogeneous mixtures separated?
Ans. Heterogeneous mixtures can be separated into their respective constituents by simple physical methods like handpicking, sieving, filtration. Sometimes special techniques have to be used for the separation of the components of a mixture.
Q57. What is heterogeneous mixture? Give examples.
Ans. A mixture in which the substances remain separate and one substance is spread throughout the other substance as small particles is called heterogeneous mixture. Example: ink, milk, coal, soil, sugar and sand mixture, soap solution, dyes etc.
Q58. While diluting a solution of salt in water, a student by mistake added acetone (boiling point 56°C). What technique can be employed to get back the acetone? Justify your choice.
Ans. The mixture of acetone and salt solution in water can be separated by distillation because difference in their boiling points is more than 25°C. Acetone will evaporate and get condensed first leaving behind the salt solution.
Q59. How can you separate a mixture of oil and water?
Ans. Two immiscible liquids, oil and water, can be separated by using Separating Funnel. The mixture of oil and water forms two separate layers because they are completely insoluble in each other. Oil forms the upper layer while water forms lower.
Q60. A child wanted to separate the mixture of dyes constituting a sample of ink. He marked a line by the ink on the filter paper and placed the filter paper in a glass containing water as shown in figure. The filter paper was removed when the water moved near the top of the filter paper.
(a) What would you expect to see, if the ink contains three different coloured components?
(b) Name the technique used by the child.
(c) Suggest one more application of this technique.
Ans. (a) The coloured component that is more soluble in water, rises faster and in this way the colours get separated. Three different coloured spots are obtained on the strip at different heights.
(c) It is used to separate drugs from blood.
Q61. Classify the following as physical or chemical properties.
(a) The composition of a sample of steel is 98% iron, 1.5% carbon and 0.5% other elements.
(b) Zinc dissolves in hydrochloric acid with the evolution of hydrogen gas.
(c) Metallic sodium is soft enough to be cut with a knife.
(d) Most metal oxides form alkalis on interacting with water.
Ans. (a) Physical property
(b) Chemical property
(c) Physical property
(d) Chemical property
Q62. Give an example each for the mixture having the following characteristics. Suggest a suitable method to separate the components of these mixtures.
(a) A volatile and a 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.
Ans. (a) Common salt solution – Evaporation or Distillation
(b) Mixture of kerosene and petrol – Distillation
(c) Mixture of oil and water - Separating funnel
(d) Mixture of ammonium chloride and common salt – Sublimation
(e) Ink - Chromatography
Q63. How is a separating funnel used in everyday life?
Write any two application of separating funnel.
Ans. Application of Separating Funnel
1. To separate mixture of oil and water.
2. In the extraction of iron from its ore, the lighter slag is removed from the top by this method to leave the molten iron at the bottom in the furnace.
Q64. Fill in the blanks.
(a) A colloid is a _______ mixture and its components can be separated by the technique known as _______.
(b) Ice, water and water vapour look different and display different _______ properties but they are _______ the same.
(c) A mixture of chloroform and water taken in a separating funnel is mixed and left undisturbed for some time. The upper layer in the separating funnel will be of _______ and the lower layer will be that of _______.
(d) A mixture of two or more miscible liquids, for which the difference in the boiling points is less than 25 K can be separated by the process called _______.
(e) When light is passed through water containing a few drops of milk, it shows a bluish tinge. This is due to the _______ of light by milk and the phenomenon is called _______. This indicates that milk is a _______
Ans. (a) heterogeneous; centrifugation
(b) physical, chemically
(c) water, chloroform
(d) fractional distillation
(e) scattering, Tyndall effect, colloidal
Q65. Calculate the mass of sodium sulphate required to prepare its 20% (mass percent) solution in 100 g of water?
Ans. Let the mass of solute be x
Mass % of solution
= Mass of Solute/(Mass of Solute + Mass of Solvent) x 100
20 = x/(x+100) x100
20(x+100) = 100x
20x + 2000 = 100x
2000 = 100x – 20x
2000 = 80x
X = 2000/80 = 25g
Q66. Fractional distillation is suitable for separation of miscible liquids with a boiling point difference of about 25 K or less. What part of fractional distillation apparatus makes it efficient and possess an advantage over a simple distillation process? Explain using a diagram.
Ans. A simple fractionating column is a tube packed with glass beads. The beads provide surface for the vapours to cool and condense repeatedly.
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