4.6 Practical skills and techniques

Question 1

When carrying out colorimetry, how would you choose an appropriate colour or wavelength of filter?

Answer 1

choosing one that is complementary to the colour of the species being tested

Question 2

How does colorimetry work?

Answer 2

it used the relationship between colour intensity of a solution and the concentration of the coloured species present

Question 3

What is a colorimeter or a spectrophotometer used for?

Answer 3

to measure the absorbance of light of a series of standard solutions, and this data is used to plot a calibration graph

Question 4

How can the concentration of the solution being tested be determined?

Answer 4

from its absorbance and by referring to the calibration curve

Question 5

What must the concentrations of the coloured species being tested do?

Answer 5

must lie in the straight line section of the calibration graph

Question 6

What is distillation used for?

Answer 6

identification and purification of organic compounds

Question 7

Explain the use of distillation in confirming the identity of a compound

Answer 7

the boiling point of a compound, determined by distillation, is one of the physical properties that can be used to confirm its identity

Question 8

How can distillation be used to purify a compound?

Answer 8

by separating it from less volatile substances in the mixture

Question 9

What is the use of heating under reflux?

Answer 9

Allows heat energy to be applied to a chemical reaction mixture over an extended period of time without volatile substances escaping

Question 10

What is the process of heating under reflux?

Answer 10

• the reaction mixture is placed in a round bottomed flask
• with anti-bumping granules
• it is then fitted to a condenser
• the flask is then heated using an appropriate source of heat

Question 11

What does vacuum filtration involve?

Answer 11

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

Question 12

What flasks can be used for vacuum filtration?

Answer 12

• Buchner
• Hirsch
• sintered glass funel

Question 13

What is the technique of recrystalisation to purify an impure solid?

Answer 13

• dissolving an impure solid gently in a minimum volume of a hot solvent
• hot filtration of the resulting mixture to remove an insoluble impurities
• cooling the filtrate slowly to allow crystals of the pure compund to form, leaving soluble impurities dissolve in the solveny
• filtering, wahing and drying the pure crystals