Instrumental methods of analysis
Instrumental methods of analysis rely on machines. There are several different types of instrumental analysis. Some are suitable for detecting and identifying A substance made of one type of atom only., while others are better suited to A substance formed by the chemical union of two or more elements..
Compared to simple laboratory tests, instrumental methods of analysis may give improved:
- The distance travelled in a known time period, eg miles per hour or kilometres per hour.
- When the value of a measurement is close to the true value.
- sensitivity (they can detect very small amounts of a substance in a small amount of sample)
Flame emission spectroscopy
The flame emission Instrument used to measure properties of light, usually to identify materials. is a scientific instrument based on flame testing. Values, typically letters or numbers. from a spectroscope can be used to:
- Identify metal Electrically charged particle, formed when an atom or molecule gains or loses electrons. in a sample.
- Determine the The concentration of a solution tells us how much of a substance is dissolved in water. The higher the concentration, the more particles of the substance are present. of metal ions in dilute Mixture formed by a solute and a solvent..
Identifying metal ions
In the flame emission spectroscope, the coloured light from a To turn from a liquid to a gas or a vapour. sample can be split to produce an Light given off by a substance, split into its component colours or wavelengths.. The different lines in an emission spectrum look like a coloured barcode. Each metal ion produces a unique emission spectrum.
The metal present in a sample is identified by comparing its A series of similar waves arranged in order of wavelength or frequency. with reference spectra. These are emission spectra from known metal ions. If two spectra match, they must be from the same metal ion.
Determining concentrations
A reading is taken from the flame spectroscope for different concentrations of a metal ion in solution. These readings are used to plot a Graph with the readings from a machine plotted against known amounts of a substance..
Worked example
A solution containing sodium ions gives a reading of four units on the flame photometer. Use the calibration curve above to determine the concentration of sodium ions in this solution.
The concentration is 0.02 g dm-3.
Question
A solution containing sodium ions gives a reading of nine units on the flame photometer. Use the calibration curve above to determine the concentration of sodium ions in this solution.
The concentration is 0.045 g dm-3.
