The Case of Solutions
The solutions are homogeneous substances and heat is also usually evolved or absorbed in the preparation of a solution. Even then a solution is considered a mixture because : (i) it can be separated into its components by physical methods, (ii) it shows the properties of its constituents, (iii) it has a variable composition, and (iv) it does not have a fixed boiling point.
For example, salt-solution is considered a mixture because of the following reasons:
(i) Salt-solution can be separated into salt and water by the physical process of distillation.
(ii) Salt-solution shows the properties of both its constituents, salt as well as water.
(iii) The composition of salt-solution is variable. Different amounts of salt can be dissolved in the same amount of water to get salt solutions having different compositions. The salt solution does not have a definite formula.
(iv) Salt-solution does not have a fixed boiling point.
Suppose we are given two liquids, one a pure compound and the other a solution, and we have to find out which one is compound and which one is solution (or mixture). In order to distinguish between the two, we should evaporate them separately. The liquid which evaporates completely, leaving no residue,is a pure compound. On the other hand, the liquid which leaves behind a residue on evaporation, is a solution or mixture. For example, pure water can be distinguished from aqueous salt-solution by evaporation. Pure water evaporates completely leaving no residue, but salt-solution leaves behind salt as residue on evaporation (Please do not say that salt-solution can be distinguished from pure water "by tasting it"!).
Notes
Matter in Our Surroundings - Notes
1. 11. Metals Usually Have a Silver or Grey Colour
Show Notes
2. The Case of a Liquid Solute Dissolved in a Liquid Solvent
Show Notes
8. 7. Non-Metals may be Solid, Liquid or Gases at the Room Temperature.
Show Notes
9. 3. Non-Metals are Bad Conductors of Heat and Electricity.
Show Notes
10. 1. Separation by a Suitable Solvent
Show Notes
11. 6. Metals are Usually Strong. They Have High Tensile Strength.
Show Notes
18. Chemical Formula for daily use material
Show Notes
20. 4. Metals are Lustrous (or Shiny), and can be Polished.
Show Notes
22. To Study the Properties of a Compound of Iron and Sulphur
Show Notes
29. To Separate a Mixture of Alcohol and Water
Show Notes
31. 3. Metals are Good Conductors of Heat and Electricity.
Show Notes
32. To Study the Properties of a Solution
Show Notes
33. 7. Metals are Solids at the Room Temperature
Show Notes
34. To Study the Properties of a Colloid
Show Notes
42. To Separate the Salt-Water Mixture (or Salt-Solution)
Show Notes
43. To Study the Properties of a Suspension
Show Notes
44. Experiment to Obtain Coloured Component (Dye) From Ink
Show Notes
49. 8. Non-Metals Have Comparatively Low Melting Points and Boiling Points
Show Notes
50. To Study the Properties of a Mixture of Iron and Sulphur
Show Notes
