chemical analysis - flame tests Flashcards
how do we identify a metal ion?
using flame tests
how to do a flame test?
first place a small amount of our chemical into wire mounted in a handle
place end of this into blue bunsen burner flame
colour of flame shows which metal ion present
what colour does the flame go if lithium is burnt?
a crimson flame
what colour does the flame go if sodium is burnt?
a yellow flame
what colour does the flame go if potassium ion is burnt?
lilac flame
what colour does the flame go if calcium ion is burnt?
orange-red
what colour does the flame go if copper ion is burnt?
a green flame
what is a difficulty about using flame tests to identify a metal ion?
- can be difficult to distinguish the colour of the flame. especially if there is a low concentration of the metal compound.
- sometimes sample contains a mixture of metal ions which can mask the colour of the flame
what other technique do scientists use instead of flame tests?
flame emission spectroscopy
what happens in flame emission spectroscopy?
a sample of the metal ion in a solution is placed into the flame. the light given out is passed into a machine called a spectroscope which converts the light into a line spectrum. the positions of the lines in the spectrum are specific for a given metal ion. you can then identify the metal ion present.
what can flame emission spectroscopy also tells us about the metal ion?
the concentration of the metal ion as the lines become more intense at a high concentration
what type of method is flame emission spectroscopy?
an instrumental method (carried out by a machine)
advantages of instrumental methods
- rapid. use flame emission spectroscopy (FES) to analyse samples more rapidly than flame tests
- sensitive. FES will work even in a tiny sample of metal compound
- accurate. FES more likely to identify metal ion correctly than using a flame test
