Instrumental Methods & Flame Emission T
The bench tests in this topic are cheap and quick, but modern labs mostly use instruments — machines that detect and identify elements and compounds automatically. They matter most when the sample is tiny or the answer must be exact, which is why forensic and drug-control scientists rely on them.
Compared with the chemical tests in this topic, instruments are:
- more accurate,
- more sensitive — they work with very small samples,
- faster, and able to run many samples automatically.
The exam phrasing to reach for is the trio accurate, sensitive and rapid.
Flame emission spectroscopy
This is the instrumental method AQA names — an example used to analyse metal ions in solution. The sample is put into a flame; the hot ions emit light; that light is passed through a spectroscope, which spreads it into a line spectrum. Because every metal ion gives its own pattern of lines, the output identifies the ions present — and the intensity of the lines measures their concentration.
You don’t need to know any element’s lines — just how to compare. The unknown’s line sits exactly under sodium’s, so the sample contains sodium ions.
🧪 Flame-emission spectroscope
The flame makes the sample’s metal ions emit light; the spectroscope spreads it into a line spectrum. Match the sample’s lines against the references to identify the ion(s) — and see how a mixture shows every ion’s lines at once, which a flame test cannot separate.
A flame test looks at one ion at a time and a strong colour can mask others. Flame emission spectroscopy gives a full line spectrum, so it can identify several ions in a mixture at once and measure how much of each is present — faster, more sensitive and more accurate than the naked eye.
🧪 Exam-style questions
Give one advantage of using an instrumental method rather than a chemical test. Tick (✓) one box.
What is one advantage of flame emission spectroscopy over a flame test? Tick (✓) one box.
An unknown solution gives a line spectrum whose lines match exactly the reference spectrum for potassium. What does this show? Tick (✓) one box.
Besides identifying which metal ions are present, what else can flame emission spectroscopy measure? Tick (✓) one box.