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.
Notes
Matter in Our Surroundings - Notes
2. 7. Metals are Solids at the Room Temperature
Show Notes
5. 3. Non-Metals are Bad Conductors of Heat and Electricity.
Show Notes
8. 11. Non-Metals Have Many Different Colours.
Show Notes
10. 7. Non-Metals may be Solid, Liquid or Gases at the Room Temperature.
Show Notes
15. 8. Metals Generally Have High Melting Points and Boiling Points.
Show Notes
19. 8. Non-Metals Have Comparatively Low Melting Points and Boiling Points
Show Notes
23. 1. Non-Metals are Not Malleable. Non-Metals are Brittle.
Show Notes
24. To Study the Properties of a Suspension
Show Notes
25. Effect of Temperature and Pressure on Solubility
Show Notes
26. Chemical Formula for daily use material
Show Notes
28. Pure Substances : Elements and Compounds
Show Notes
33. 1. Separation by a Suitable Solvent
Show Notes
34. Solutions, Suspensions And Colloids
Show Notes
37. 3. Metals are Good Conductors of Heat and Electricity.
Show Notes
39. 4. Non-Metals are Not Lustrous (Not Shiny). They are Dull in Appearance.
Show Notes
48. Separation Of Mixture Of a Solid And a Liquids
Show Notes
49. To Separate the Salt-Water Mixture (or Salt-Solution)
Show Notes
50. 1. Separation by Fractional Distillation
Show Notes