Flame emission spectroscopy identifies metal ions by the colour of the line spectrum they produce when their electrons are excited in a flame. Different metal ions emit light at characteristic wavelengths, producing a unique pattern of coloured lines.
How It Works (Qualitative — GCSE level)
- A small sample containing the metal ion is introduced into a hot flame.
- Energy from the flame excites electrons in the metal ions to higher energy levels.
- When electrons fall back to their ground state, they emit light at specific wavelengths.
- The emitted light is passed through a prism or diffraction grating to produce a line spectrum.
- The pattern of lines is unique to each element — like a fingerprint.
Metal Ions Identified by Flame Emission Spectroscopy
| Metal Ion | Flame Colour (simple test) | Line Spectrum |
|---|---|---|
| Lithium (Li⁺) | Crimson red | Distinctive red lines |
| Sodium (Na⁺) | Yellow/orange | Strong yellow line at 589 nm |
| Potassium (K⁺) | Lilac/violet | Red and violet lines |
| Calcium (Ca²⁺) | Orange-red | Orange and red lines |
| Copper (Cu²⁺) | Green / blue-green | Green lines |
A spectrometer separates the emitted light into a line spectrum. The position of the lines identifies the element; the intensity of the lines can be used to determine concentration.
This deep dive covers Flame Emission Spectroscopy within Instrumental Analysis for GCSE Chemistry. Revise Instrumental Analysis in Chemical Analysis for GCSE Chemistry with 6 exam-style questions and 6 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 4 of 12 in this topic. Use this deep dive to connect the idea to the wider topic before moving on to questions and flashcards.
Practice questions for Instrumental Analysis
Which formula correctly calculates the Rf value in chromatography?
State two advantages of using instrumental methods of analysis compared with traditional chemical tests.