Experiment to Obtain Coloured Component (Dye) From Ink
We take a beaker and fill it half with water (This will serve as a water bath). About 5 mL of ink (blue ink or black ink) is put in a china dish. The china dish containing ink is then placed over the mouth of beaker containing water,which is kept on a tripod stand [see Figure 72(a)].We now start heating the beaker with a burner. Soon, the water in beaker starts boiling to form steam. This steam heats the ink in the china dish. Due to this heating, the water present in ink starts evaporating gradually. When all the water has evaporated from ink, we stop heating. We will find that a small amount of a solid coloured material is left in the china dish [see Figure 72 (b)]. This coloured material is the dye which was present in the ink.Thus, water has evaporated from the ink and solid dye is left behind.This experiment shows that ink is not a single substance (or pure substance),it is a mixture. Ink is a mixture of dye in water.
We have just discussed the separation of a solid from a solution by the process of evaporation. In evaporation, we have to heat the solution to dryness. So, evaporation gives us the solid substance in the form of a powder. Moreover,if any impurities were present in the dissolved solid substance,the same will also be present when it is recovered by evaporation. This, however, is not so in the case of crystallisation.
The process of separation called 'crystallisation' gives us proper crystals (solid particles with flat sides),and impurities also get removed in it. So, in a way, crystallisation is a method of purifying solid substances in which crystals of the pure substance are formed.
The process of crystallisation also begins by evaporating the liquid mixture by heating but it is not continued till dryness. Rather, when the solution becomes sufficiently concentrated (or saturated), heating is stopped and hot concentrated solution is allowed to cool slowly. After some time, the crystals of pure solid substance appear in the solution. Keeping these points in mind, let us study the process of crystallisation in somewhat detail.
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Matter in Our Surroundings - Notes
1. 3. Non-Metals are Bad Conductors of Heat and Electricity.
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3. 7. Metals are Solids at the Room Temperature
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4. The Case of a Liquid Solute Dissolved in a Liquid Solvent
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6. 11. Metals Usually Have a Silver or Grey Colour
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7. 7. Non-Metals may be Solid, Liquid or Gases at the Room Temperature.
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11. 6. Non-Metals are Not Strong. They Have Low Tensile Strength.
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13. Separation Of Mixture Of a Solid And a Liquids
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15. To Study the Properties of a Colloid
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19. To Study the Properties of a Compound of Iron and Sulphur
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20. 1. Separation by a Suitable Solvent
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21. 11. Non-Metals Have Many Different Colours.
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25. 6. Metals are Usually Strong. They Have High Tensile Strength.
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26. 3. Metals are Good Conductors of Heat and Electricity.
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30. 2. Separation by a Separating Funnel
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31. To Distinguish a Colloid from a Solution
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35. Experiment to Obtain Coloured Component (Dye) From Ink
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38. To Study the Properties of a Solution
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40. 1. Separation by Fractional Distillation
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42. 1. Non-Metals are Not Malleable. Non-Metals are Brittle.
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44. To Separate the Salt-Water Mixture (or Salt-Solution)
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45. Chemical Formula for daily use material
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50. To Study the Properties of a Suspension
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