Unit 4f Practical Skills And Techniques

Question 1

Colorimetry

Answer 1

Used to measure the concentration of a species based on its absorption of a particular wavelength of light

Question 2

What is involved with colorimetry?

Answer 2

Prepare a series of standard solutions
Choose appropriate colour of filter complimentary to colour of species being tested
Preparing a calibration curve

Question 3

Distillation

Answer 3

Used for identification and purification of organic compounds

Question 4

Heating under reflux

Answer 4

Allows heat energy to be applied to a reaction mixture over time without volatile substances escaping

Question 5

Vacuum Filtration

Answer 5

carrying out a filtration under reduced pressure and provides a
faster means of separating a precipitate from a filtrate.

using a suction pump to help speed up the time taken for the filtration to take place.

Question 6

Recrystallisation

Answer 6

Dissolve in small volume of appropriate solvent
Heat ( to dissolve compound and impurities)
Filter ( done with hot funnel and flask)
Cool

Question 7

What properties should a recrystallisation solvent have?

Answer 7

Desired product is sparingly soluble at low temperatures but readily soluble at high temperatures.

Neither compound nor impurities should react with the solvent.

Boiling pt should not be so low that it would evaporate during heating.

Question 8

Why should a saturated solution be cooled slowly during recrystallisation?

Answer 8

To allow pure crystals to form and keep impurities in solution

Question 9

Solvent Extraction

Answer 9

Used to isolate a solute from solution by using a 2nd immiscible solvent in which the solute is more soluble

Question 10

What are the requirements for solvent extraction

Answer 10

Question 11

What’s is meant by partition coefficient?

Answer 11

the concentration of a solute in the organic layer over that in the aqueous layer.