C2 - Analysing Substances Flashcards
How does chromatography purify substances?
The substance that needs to be purified will be separated from other substances which makes it pure
How does chromatography find out which substances are present?
The substances are separated from each other meaning that they are pure so we can analyse which substances are present
What is paper chromatography?
A type of chromatography where colours present in a substance travel up the paper at different rates
Give the 2 uses of chromatography
Chemical analysis that finds out what the substances present are
Synthesis (purifying substances)
What is chromatography?
A chemical process that separates mixtures of dissolved substances
What is the stationary phase?
The part of the chromatography equipment that does not move and is usually solid
What is the stationary phase in paper chromatography?
Filter paper
What is the mobile phase?
The part of the chromatography that pushes the substances across the stationary phase
What is the mobile phase in paper chromotography?
Solvent
What is a chromatogram?
The filter paper in paper chromatography with the spots at different heights after the chromatography has taken place
Why do we use reference substances?
So that we can see if some of the unknown substances are actually the reference substances
How do we know if an unknown substance and a reference substance are the same?
They will be level in height on the chromatogram
Why can’t some substances be detected by colour on the chromatogram?
They are colourless substances
What do we do to distinguish invisible spots?
Dip the filter paper in locating agent
What is a locating agent?
A chemical that reacts with a substance to form a coloured compound
What is thin layer chromatography?
A variant of paper chromatography that uses silica plates instead of filter paper as a stationary phase
What is the advantage of using thin layer chromatography instead of paper chromatography?
Small quantities of the substances can be used
Why do some substances move across the mobile phase at different speeds than each other?
Some substances have an equilibrium position that favours the mobile phase more or less than others
What is chemical analysis?
Analysing substances to find out their chemical composition and structure
What is gas chromatography?
A form of chromatography that uses a carrier gas as a mobile phase and is very accurate
Which substances are used as carrier gases and why?
Argon and nitrogen
They are inert (don’t react)
Describe gas chromatography
The substances are heated until they become gases
The carrier gas brings the substances along a tube and they pass a sensor
The fact that they travel at different speeds means that they will go through the sensor at different times
What is retention?
How much a substance holds back (favours the stationary phase)
What is a mass spectrometer?
An instrument that weighs molecules and tells us the molecular mass of substances
