Separation techniques Flashcards
1
Q
What are some disadvantages of evaporation to dryness
A
- Solid obtained might not be pure
- Cannot be used to obtain thermally unstable solids
2
Q
When to use crystallisation instead of evaporation to dryness
A
- Obtain pure solid
- Obtain hydrated salts
- Obtain thermally unstable solids
3
Q
When to use evaporation to dryness instead of crystallisation
A
- Solubility of salt does not change significantly with temperature changes
4
Q
Why are boiling chips used in simple distillation
A
Ensure a smooth boiling process
4
Q
Is Rf value larger or smaller than 1
A
SMALLER
4
Q
What are some substances that sublime
A
- Iodine
- Ammonium chloride
- Naphthalene
- Solid carbon dioxide
5
Q
How to tell if a solid is impure
A
- Melting point decreases
- Melts over a range of temperatures
6
Q
How to tell is a liquid is impure
A
- Boiling point increases
- Boils over a range of temperatures
6
Q
When is paper chromatography used to test for substance purity
A
- Substance cannot be melted or boiled easily
- Amount of substance is very small
7
Q
What gases are soluble in water
A
- NH3
- HCl
- Cl2
- SO2
7
Q
What gases are alkaline
A
NH3
8
Q
What is the Mr of air
A
29.0
9
Q
How to collect water soluble gases
A
Upwards or downwards displacement of air
10
Q
What gases are neutral
A
- O2
- H2
- N2
- CO
11
Q
How to collect water insoluble gases
A
Displacement of water
