Pure And Impure Substances Flashcards
What is a pure substance ?
A pure substances contains only one type of element of compound
What can pure substances do ?
Melt and solidify at one temperature (melting point)
Boil and condense at one temperature (boiling point)
If a substance melts over a range of temperatures. What is it?
Impure substance because pure substances have a fixed melting point
What is a formulation?
A mixture that has been designed as a useful product
Eg medicine, paint, fuels and fertilisers
How does chromatography work?
It separates components based on their solubility
What is a solvent ?
The liquid in which a solute dissolves in to form a solution (mobile phase - water)
What’s a mobile phase in chromatography?
A phase in chromatography that moves which is usually the solvent of mixtures
What’s a stationary phase in chromatography?
Phase in chromatography that doesn’t move (eg the absorbent paper)
Why is the start line always drawn in pencil?
Because pencil is insoluble and the ink of the pen would separate
Why shouldn’t the solvent touch the ink straight away?
The ink would contaminate the results
How do you calculate the retention factor (Rf) ?
Rf = distance moved by substance / distance moved by solvent
Why do you calculate the retention factor - Rf ?
It allows us to identify substances we have found by comparing this with a database.
The larger the Rf the more soluble the substance is.
