subject - chemistry
class - 9th
Answers
Answer: 1. The solid is impure.
If the melting point of the solid has a large difference of over 10 C then there must be impurities present in the sample of solid taken.
Impurities in a solid cause a melting point depression because the impurity disrupts the crystal lattice energies. If the impurity present stabilizes the solid by say hydrogen bonding, then the impurity causes the melting point of the impure solid to increase instead of usually decreasing.
Thus the melting point of impure solid determined experimentally comes out to be 160 C but its melting point given in standard textbooks is 150 C for pure solid.
2. By Fractional Distillation.
Since the boiling point of the 2 liquids are not far off. It can be separated by Fractional distillation where the liquid with the lower boiling point (60 degree celsius) will evaporate first and will be going through a condenser and condensed and put into a separate flask before the other liquid begins to evaporate.
3.
(a) In a colloidal solution, the particle size is such (1 nm to 100 nm), that these particles scatter the light rays as they fall on them. Because of scattering, the path of the light as well as the particles become visible. But in a true solution, the particle size is so small (less than 1nm) that these particles are not in a position to scatter the light. Therefore, true solution does not show any Tyndall effect.
(b) In dirty clothes, the dust particles are sticking on the oil drops present. Simple water cannot remove these oil drops from the clothes because water and oil as such do not form a stable emulsion. Soap plays the role of emulsifier and helps in forming a stable emulsion between the two. In other words, it helps in mixing oil and water. This means that soap helps in removing these oil drops along with the dirt sticking to them. The dirty clothes get washed by soap solution.
4. A saturated solution can be made unsaturated either by adding more solvent to the solution or by increasing the temperature.
5. Chemical changes are:
(a) Growth of a plant (b) Rusting of iron
(c) Cooking of food (d) Digestion of food
(e) Burning of a candle
Explanation: