Standard level
When metal ions become excited by heat or electricity, the electrons produce an emission spectrum that we observe as a colour formed by combining all of the emitted wavelengths.
Background
Emission spectra contain discrete wavelengths of light that combine to give colour. In this experiment, the students will observe the colour emitted by different salts.
Lithium emission spectrum
Chemicals
- Lithium chloride
- Sodium chloride
- Potassium chloride
- Magnesium chloride
- Strontium chloride
- Barium chloride
- Copper(II) chloride
- Concentrated hydrochloric acid
- Water
Apparatus
- Nichrome wire
- Large Bunsen burner
- Beaker, 50ml (x2)
- Each station has a small beaker of concentrated hydrochloric acid and a small beaker of water.
- A length of nichrome wire is twisted at one end forming a small loop.
- The nichrome wire loop is cleaned by dipping it into the concentrated hydrochloric acid followed by the water.
- A few crystals of the compound to be tested is picked up by the wet loop.
- The crystals are held at the bottom edge of a hot transparent Bunsen flame and the colour observed. It will only appear for a short time.
It is important to carry out the test for sodium salts in a fume cupboard. The sodium colour is due to two intense lines in the spectrum and any sodium contamination in the air will adversely affect all of the other results.
Sodium emission spectrum
