Compare evaporation, crystallization and distillation. Class 9
Compare evaporation, crystallization and distillation. Class 9
Question 1.
Compare evaporation, crystallization and distillation. In which situation, would you prefer each of these over the others? Class 9
Answer:
Evaporation: Removes solvent by heating; solute is left behind as a solid. Prefer when we want to obtain the solute and do not need the solvent. Example: Getting salt from saltwater, concentrating a solution. Not suitable when solute decomposes on heating.
Crystallization: Controlled cooling of a saturated solution to obtain pure crystals of the solute. Prefer when we want pure crystals of the solute, or when two solids are both dissolved in the same solvent and need to be separated. Best when solute's solubility changes significantly with temperature. Example: Purifying copper , sulfate, separating potassium nitrate from sodium chloride.
Distillation: Separates two miscible liquids with different boiling points (>25°C), or separates solvent from solute while recovering both. Prefer when we need to separate two miscible liquids, OR when we want to recover both the solute (in the flask) and the solvent (as distillate). Example: Separating acetone and water; purifying water.
Question 2.
Blood is an example of a colloidal mixture. Class 9
(i) What would happen if blood behaved like a true suspension inside the body?
(ii) In a blood sample, identify the dispersed phase and the dispersion medium.
Answer:
(i) If blood behaved like a true suspension, its particles (red blood cells, white blood cells, platelets) would settle down to the bottom due to gravity, just like mud particles settle in muddy water. This would make blood unable to flow properly through the blood vessels. The cells would not be distributed throughout the bloodstream, which would prevent the delivery of oxygen and nutrients to body tissues. This would be fatal - the body's organs would fail due to lack of oxygen and nutrients.
(ii) Dispersed phase: Blood cells - red blood cells (RBCs), white blood cells (WBCs), and platelets.
Dispersion medium: Blood plasma (the yellowish liquid that makes up most of the blood).