Chemistry/Distillation Marking Scheme

MARKING SCHEME FOR SCIENCE 8 EXPERIMENT DISTILLATION

Maximum = 8

Observations: (2)
 * The original solution was a blue liquid. When the solution is heated, boiling starts and a clear, colourless liquid forms in the cold test tube . As time passes, the amount of colourless liquid increases and the volume of blue liquid decreases . The blue liquid gets darker and darker as its volume decreases. When the last of the blue liquid has evaporated, a blue residue remains.

Discussion: 1.	Describe the solution at the start of the experiment. (1) At the start of the experiment, the solution was a transparent blue liquid.

2.	Describe 	(a)	the distillate, and 		(b) 	the residue in the flask (1/2)		The distillate is a clear, colourless liquid. (1/2)		The residue is a blue solid.

3.	What evidence do you have that the distillation process separated the solvent and the solute? (1)		The solvent and solute were seen to be separated because the solvent was present in the test tube and the solute remained behind in the flask.

4.	Identify the two changes of state that occurred in this experiment and describe where in the distillation apparatus each change of state occurred. (1)		The solvent boiled (changed from a liquid to a gas) in the flask and (1) 		condensed (changed from a gas to a liquid) in the test tube.

5.	What was the purpose of the ice water? (1)		The ice water helped cool the gas and help the gas condense back to a liquid.