Explain why the temperature reamins constant during melting / boiling?
The heat energy absorbed by the particles is used to overcome the forces of attarction holding them together.
Explain why during freezing, the temparture remains constant?
This is because heat loss to the surroundings is exactly balanced by the heat energy liberated as the particles attract one another to form a solid.
Boiling :-
*occurs only at a fixed temperature
*occurs throughout a liquid
*occcurs rapidly
Evaporation :-
*occurs at tempearature below boiling point
*occurs only at the surface of the liquid
*occurs slowly
Use kinetic particle theory to explain why the bromine could be smelt on the other side of the room.
The particles at the surface of liquid bromine have sufficient energy to break into the gas state. They then move rapidly and randomly in the room until equilibrium is reached by the process of diffusion.
Explain what is meant by Rf value.
Rf stands for Retention Factor and it is thr ratio of distance travlelled by substance/spot to the distance travlelled by the solvent.
What is a saturated solution?
A saturated solution is a solution which contains the maximum amount of a solute at a given temperature.
What is the purpose of adding boiling chips or boiling stones in the distillation flask?
The presence of the boiling stones in the distillation flask ensures that the liquid boils smoothly (prevent splashing)
Explain why the thermometer is placed at the side arm of the distillation flask.
This is because the thermometer measures the boling point of the solvent that is being distilled over.
Explain why the condenser slopes downwards.
This ensures that the solvent vapours which is being condensed runs easily into the receiver (beaker) and not back in the distillation flask.
What is the purpose of the condenser?
The condenser cools down the hot vapours into the liquid state.
the solvent which is obtained is called a distillate.
What is the purpose of the fractionating column during fractional distillation?
The fractionating column is packed with glass beads which provide a large surface area for the condensation of vapour. The fracitonating column enables an effective separation of he 2 liquids.
Explain why a pencil is used to draw the baseline and not a pen.
The graphite of the pencil does not dissolve in the solvent while the dyes in the ink dissolve in the solvent and produce spots which will interfere with the results.
Explain why the level of the solvent should be below the pencil/base line.
This will lead to immediate dissolving of the spot and no separation will be obained.
Explain why the glass tank containing the chromatography paper and the solvent is covered with a lid.
The lid prevents evaporation of the solvent which is volatile.