Experimental Technique Ex 9

Experimental Technique Ex 9 ANSWERT KEY Section A Q 1 Q 2 Q 3 Q 4 Q 5

D

Q6

A

C

Q7

D

B

Q8

B

D

Q9

C

B

Q1 0

A

Q1 1 Q1 2 Q1 3 Q1 4 Q1 5

C C D C A

Q1 6 Q1 7 Q1 8 Q1 9 Q2 0

D

Q21

D

A

Q22

A

D

Q23

C

A

Q24

A

D

Q25

A

Section B 1

(a),( b)

* Pls include thermometer ( place it near to the delivery tube) ink h

(c) (d) 2

c

Separated water

(b)

Distillation /simple distillation To provide a cold environment to condense the water vapor into the liquid water. The spots made by the ions were colourless. The locating agent allow the spots on the chromatogram to be seen. Working: Rf = 0.75 = (distance travelledsubstance) / (distance travelledsolvent) Thus, 0.75 = = (distance travelledsubstance) / (8) Distance travelled substance = 6. Draw the ‘spot’ for Fe2+ with the height 6 units.

(c) (d)

Iron, copper and zinc If the solvent travels to the top of the chromatography, the solvent front

(a)

(e) (f)

(g) (h)

cannot be determined. Hence, Rf value cannot be calculated. The metal ions are not soluble in the solvent used. (i) Pencil lead is insoluble in the solvent, whereas pen ink contains dyes which will interfere with the results on the chromatogram. (ii) To prevent the spots from mixing and interfering with each others’ results on the chromatogram. Accurate results can then be obtained. (iii) To allow the spots to be fully separated into their components on the chromatogram. Spots with greater solubility in the solvent will travel up the chromatogram than spots that are less soluble. (i) To allow the solvent to travel up to the spot of the chemical. (ii) (iii) 1. This is an ascending method . The solvent ascends the chromatogram against gravity. Hence, process will be slower. 2. The colour of the spots will overlap each other, the results will not be accurate.

3

a(i) (ii)

A stirrer is used to ensure that the heat is spread throughout the water evenly. The melting point of the solid is low, between 50°C-60°C. Heating too quickly might cause the melting process to be missed.

b c

The solid will melt over a range of temperature. 1. To determine the melting point of a solid that melts above 100°C, a water bath cannot be used as water boils at 100°C. Instead, use an oil bath as the melting point of oil is higher than water. 2. The thermometer used can only measure up to 110°C. However, the solid melts > 120°C which is beyond the temperature range of the thermometer. Hence, use a thermometer that can measure temperature from 0°C-150°C