chemical analysis Flashcards
What is a pure substance?
A pure substance is a single element or compound, not mixed with any other substances.
How can you distinguish pure substances from mixtures?
Pure elements and compounds have a specific fixed melting and boiling point, which can be used to distinguish mixtures from pure substances as mixtures melt and boil over a range of temperatures.
What is an impure substance?
An impure substance is a mixture.
What is a formulation?
A formulation is a mixture that has been designed for a useful product. The quantity of each component is carefully measured to ensure that the product has the required properties.
What is chromatography?
Paper chromatography is a separation technique, which is a physical process. It allows substances to be separated based on their solubilities.
What is a physical process?
A physical process is a separation technique which does not involve chemical reactions and no new substances are made.
What is the stationary phase in chromatography?
The stationary phase in chromatography is the paper as it does not move.
What is the mobile phase in chromatography?
The mobile phase in chromatography is the solvent as it moves.
What is a solvent?
A solvent is a liquid that will dissolve a substance.
How can a mixture be identified in chromatography?
A mixture can be identified in chromatography as it will separate into multiple dots on the chromatogram. These spots may be different in different solvents.
How can a pure substance be identified in chromatography?
A pure substance can be identified in chromatography as it will remain as one dot on the chromatogram. This is the same spot at the same level in all solvents.
How does chromatography work?
Paper chromatography works because the chemical is attracted to the stationary phases to a different extent. If they are strongly attracted, they won’t move far.
Why is the line on chromatography paper in pencil?
The line is in pencil as it does not travel up the solvent.
What does it mean if two dots are at the same level on two different chromatograms?
They are the same substance.
How do you calculate the Rf value?
Rf = distance moved by chemical / distance moved by solvent
- each substance has a different Rf value
- some may have the same Rf value, so repeat to narrow it down
Why are flame tests not good for a mixture of ions?
Flame tests are not good for a mixture of ions as some of the flame colours may be masked.
Describe how flame emission spectroscopy works.
flame emission spectroscopy:
- a sample of a metal ion is placed into a flame
- the light given out is passed through a spectroscope
- this coverts the light into a line spectrum, and these lines are specific to the metal ion
- the concentration can be told as higher conc. means thicker lines
- this is an instrumental method
Give seven examples of formulations.
formulation examples:
- fuels
- cleaning agents
- paints
- medicine
- alloys
- fertilisers
- food
Give three examples of why flame emission spectroscopy (instrumental method) is better than flame tests.
flame emission spectroscopy > flame tests as:
- they are more rapid
- they are more sensitive (FES will work on a tiny sample)
- they are more accurate
