4.6 practical skills and techniques

Question 1

techniques involved in colorimetry

Answer 1

• preparing a series of standard solutions of appropriate concentration
• choosing an appropriate colour or wavelength of filter complementary to the colour of the species being tested
• using a blank
• preparing a calibration graph

Question 2

colorimetry relationship

Answer 2

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

Question 3

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

Answer 3

colorimetry

Question 4

colorimetry method

Answer 4

• A colorimeter or a spectrophotometer is used to measure the absorbance of light of a series of standard solutions, and this data is used to plot a calibration graph
• The concentration of the solution being tested is determined from its absorbance and by referring to the calibration curve
• The concentration of coloured species in the solution being tested must lie in the straight line section of the calibration graph

Question 5

distillation method

Answer 5

• Candidates must be familiar with use of the technique of distillation. Distillation is used for identification and purification of organic compounds
• The boiling point of a compound, determined by distillation, is one of the physical properties that can be used to confirm its identity
• Distillation can be used to purify a compound by separating it from less volatile substances in the mixture

Question 6

• Candidates must be familiar with use of the technique of distillation. Distillation is used for identification and purification of organic compounds
• The boiling point of a compound, determined by distillation, is one of the physical properties that can be used to confirm its identity
• Distillation can be used to purify a compound by separating it from less volatile substances in the mixture

Answer 6

distillation method

Question 7

• A colorimeter or a spectrophotometer is used to measure the absorbance of light of a series of standard solutions, and this data is used to plot a calibration graph
• The concentration of the solution being tested is determined from its absorbance and by referring to the calibration curve
• The concentration of coloured species in the solution being tested must lie in the straight line section of the calibration graph

Answer 7

colorimetry method

Question 8

Heating under reflux method

Answer 8

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

Question 9

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

Answer 9

Heating under reflux

Question 10

Heating under reflux purpose

Answer 10

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

Question 12

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

Answer 12

Heating under reflux

Question 13

Vacuum filtration method

Answer 13

• involves carrying out a filtration under reduced pressure
• provides a faster means of separating a precipitate from a filtrate
• a Buchner, hirsch, or sintered glass funnel can be used

Question 14

• involves carrying out a filtration under reduced pressure
• provides a faster means of separating a precipitate from a filtrate
• a Buchner, hirsch, or sintered glass funnel can be used

Answer 14

Vacuum filtration

Question 15

Recrystallisation method

Answer 15

• dissolving an impure solid gently on a minimum volume of hot solvent
• hot filtration of the resulting mixture to remove any insoluable impurities
• cooling the filtrate slowly to allow crystals of the pure compound to form, leaving soluable impurities dissolved in the solvent
• filtering, washing, and drying the pure crystals
• the solvent is chosen so that the compound being purified is completely soluable at high temperatures and only sparingly soluable at lower temperatures

Question 16

• dissolving an impure solid gently on a minimum volume of hot solvent
• hot filtration of the resulting mixture to remove any insoluable impurities
• cooling the filtrate slowly to allow crystals of the pure compound to form, leaving soluable impurities dissolved in the solvent
• filtering, washing, and drying the pure crystals
• the solvent is chosen so that the compound being purified is completely soluable at high temperatures and only sparingly soluable at lower temperatures

Answer 16

Recrystallisation

Question 17

Solvent extraction

Answer 17

• isolating a solute from a liquid mixture or solution by extraction using an immiscible solvent in which the solute is soluable
• two immiscible solvents form two layers in the separating funnel. The solute dissolves in both solvents and an equilibrium is established between the two layers
• the lower layer is run off into a container and the upper layer is poured into a second container
• repeated to maximise the quantity of solute extracted
• solute should be: immiscible with the liquid mixture/solution, one in which the solute is more soluable in then the liquid mixture/solution, volatile, un reactive with solute

Question 18

MP

Answer 18

The temperature range over which the solid first starts to melt, to when all of the solid has melted

Question 19

The temperature range over which the solid first starts to melt, to when all of the solid has melted

Answer 19

MP