C8 - Chemical Analysis Flashcards
What is a pure substance?
- Means nothing has been added to it, so it’s in its neutral state
- Something that only contains one compound or element throughout - not mixed with anything else
Why are melting and boiling points important for a substance?
They can determine how chemically pure a substance is, as chemically pure substances will melt or boil at a specific temperature
What are the typical features of impure substances?
- Lower melting points
- Increase melting range
- Increase boiling points
What are formulations?
Useful mixtures with a precise purpose that are made by following a ‘formula’
Give examples of formulations
- Fuels
- Cleaning agents
- Metal alloys
- Fertilisers
- Medicines
What is chromatography?
An analytical method used to seperate the substances in a mixture. You can then use it to identify the substances
What are the 2 different phrases in chromatography?
- Mobile
- Stationary
Mobile phase
The molecules can move, this is always a liquid or a gas
Stationary phase
The molecules can’t move. This can be a solid or a really thick liquid
What is formed during the mobile and stationary phases?
Equilibrium
What are the links between the mobile and stationary phase?
- The mobile phase moves through the stationary phase, and anything dissolved in the movile phase moves with it
- How quickly a chemical moves depends on how it’s ‘distributed’ between the two phases - whether it spends more time in the movile phase or the stationary phase
Distance of mobile vs stationary?
Chemicals that spend more time in the mobile phase than the stationary phase will move further through the stationary phase
Chromatogram
The result of chromatology analysis
What is the Rf value?
- The ratio between the distance travelled by the dissolved substance and the distance travelled by the solvent.
- The further through the stationary phase a substance moves, the larger the Rf value
Rf formula
Distance travelled by substance b / distance travelled by solvent
