chpt 2 methods of purification and analysis

Question 1

What are diatomic molecules and polyatomic molecules ?

Answer 1

Molecules that are formed by chemically combining 2 atoms (diatomic)
Molecules that are formed by chemically combining 3 or more atoms (polyatomic)

Question 2

Define process of filtration.

Answer 2

1. separate insoluble solid from liquid
2. pass through filter funnel
3. collect liquid in beaker

Question 3

Define process of evaporation to dryness.

Answer 3

1. soluble solid from solution
2. works for thermally stable solids (solids that do not decompose easily upon strong heating)
3. heat to saturation
4. soluble impurities MIGHT still remain in solid residue after evaporation

Question 4

Define process of crystallisation.

Answer 4

1. separates soluble solid from solution, forming pure crystals of the solid
2. heat to saturation
3. cool to allow crystals to form
4. filter mixture to obtain crystals as residue
5. wash w little cold distilled water
6. pat dry with 2 pieces filter paper

Question 5

Define process of simple distillation.

Answer 5

1. separate pure solvent from solution
2. heat up solution after putting boiling chips (used to smoothen boiling to prevent liquid from being heated past bp) in the solution
3. pure water vapour rises into condenser and condenses on cooler bottom of condenser (cold water enter from bottom, hot water leave from top)
4. water collected in beaker

Question 6

Define process of fractional distillation.

Answer 6

1. separate miscible liquids with diff bp
2. heat liquid containing boiling chips
3. vapours pass through fractionating column with glass beads
4. glass beads used as they have large surface area to volume ratio for cooling of vapours
5. liquid with lower bp passes through beads into condenser
6. liquid with higher bp condenses on beads and falls back into round bottomed flask
7. water in from bottom of condenser, water out from top for better condensation of liquid with lower bp

Question 7

Define process of chromatography.

Answer 7

1. separate 2 or more components that dissolve in same solvent
2. more soluble component travels faster and further up paper than less soluble components
3. red line drawn with pencil to show starting line
4. paper dipped in solvent just below line
5. components separated
6. solvent front is distance reached by solvent
7. locating agents used to colourless solvents eg amino acids -> allows for visible measurements to determine Rf value (ratio of distance travelled by substance relative to that travelled by solvent)

Question 8

Define process of chromatography.

Answer 8

1. separate 2 or more components that dissolve in same solvent
2. more soluble component travels faster and further up paper than less soluble components
3. red line drawn with pencil to show starting line
4. paper dipped in solvent just below line
5. components separated
6. solvent front is distance reached by solvent
7. locating agents used to colourless solvents eg amino acids -> allows for visible measurements to determine Rf value (ratio of distance travelled by substance relative to that travelled by solvent)