Flame Emission Spectroscopy (OCR GCSE Chemistry A (Gateway Science Suite)): Revision Notes
📚 Revision Notes
8.3.8 Flame Emission Spectroscopy
Flame emission spectroscopy
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Flame emission spectroscopy is a powerful technique used to analyse the elements and ions present in a sample. This method involves placing a sample in a flame, which causes it to burn and emit light. The emitted light is then passed through a spectrometer, which detects the different wavelengths of radiation. The information gathered by the spectrometer is used to produce a visual output known as a line spectrum.
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How Flame Emission Spectroscopy Works
- Sample in Flame:
- When a sample is placed in the flame, the heat causes the electrons in the atoms or ions of the sample to become excited. This means the electrons jump to higher energy levels.
- Emission of Radiation:
- As these excited electrons return to their original, lower energy levels, they release energy in the form of radiation. This radiation often falls within the visible spectrum, meaning it corresponds to specific colours.
- Formation of Line Spectrum:
- The spectrometer captures the emitted radiation and produces a line spectrum. A line spectrum consists of narrow lines at specific wavelengths, each line representing a particular emission of light by the sample.
- The pattern of lines in the spectrum is unique to the specific ions or atoms in the sample, allowing scientists to identify which elements are present.
Unique Spectra for Identification
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The line spectrum produced by a sample is like a fingerprint—it is unique to the specific ions or atoms in that sample. The exact position of the lines in the spectrum depends on the charge and electron configuration of the ions or atoms.
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Example:
- The line spectrum for hydrogen will have lines at specific wavelengths that are different from those of sodium or any other element.
- If a sample contains a mixture of hydrogen and sodium, the resulting line spectrum will show lines corresponding to both elements. By knowing the expected lines for each element, scientists can identify the presence of each one in the mixture.
Applications of Flame Emission Spectroscopy
- Astrophysics:
- Flame emission spectroscopy has been crucial in studying the composition of stars and other celestial bodies. For example, by analysing the line spectrum of the Sun, scientists were able to determine which elements are present in its atmosphere by matching the observed spectra with known spectra of elements.
- Determining Concentrations:
- Beyond identifying elements, flame emission spectroscopy can also be used to measure the concentration of ions in a sample. The intensity of the emission lines in a spectrum is proportional to the number of atoms or ions producing them. This means that by analysing the intensity, scientists can calculate the concentration of specific ions in the sample.