Flame emission spectroscopy: reading the light a metal gives off
Definition
Flame emission spectroscopy
An instrumental method that identifies metal ions in a solution and measures their concentration from the line spectrum they produce in a flame.
Definition
Line spectrum
A pattern of separate coloured lines given out by a hot element, with a set of line positions that is unique to each element.
- Flame emission spectroscopy is an instrumental method for analysing metal ions in solution.
- The sample solution is placed into a flame, and the light it gives out is passed into a spectroscope.
- The spectroscope splits that light into a line spectrum, a set of coloured lines.
Key Idea
- Each metal ion produces its own pattern of lines, which acts like a fingerprint.
- The spectrum carries two pieces of information: which metal is present and how much of it there is.
Reading the spectrum: identity and amount
Definition
Wavelength
The distance between corresponding points on successive waves, used here to describe the position of a line in an emission spectrum.
Definition
Intensity
A measure of the strength of a spectral line produced by emitted light.
- The positions of the lines, their wavelengths, identify the metal ion, because each metal has its own pattern.
- The intensity, or brightness, of the lines shows the concentration of that ion.
- A brighter line means a higher concentration of the metal ion.
- Because the lines are separate, the method can identify several metals in a mixture and measure each one.
Exam technique
- Split the mark: line position tells you which metal, and line intensity tells you how much.
- A concentration is read by comparing the intensity with lines from known standard solutions.
Why it beats a simple flame test
- A flame test gives one overall colour, which fails when several metals are mixed together.
- Flame emission spectroscopy separates the light into distinct lines, so each metal is seen on its own.
- It also measures concentration, which a simple flame test cannot do.
Self review
- What type of sample does flame emission spectroscopy analyse?
- Outline how a line spectrum is produced from a solution.
- What does the position of a line tell you, and what does its intensity tell you?
- Give one advantage of flame emission spectroscopy over a simple flame test.
