How To Demonstrate A Classic Flame Test

In this video, Paul Cook shows you how to demonstrate a classic flame test which is a qualitative analytical technique used to identify certain elements present in a sample by observing the characteristic colours produced when the sample is introduced into a flame.

When certain elements are heated in a flame, the electrons in their atoms get excited to higher energy levels. As the electrons return to their ground state, they emit light at specific wavelengths, which correspond to different colours. In this test, alcohol (IDA/IMS only)  is added to a series of borosilicate beakers or crystallizing dishes containing metal salts and boric acid. The vapour is ignited and coloured flames are observed.

The flame test is particularly useful for the identifying metal ions topic in GCSE Chemistry, as they tend to produce easily distinguishable colours. However, it is essential to note that the flame test alone may not be sufficient to identify all elements definitively, as some elements may exhibit similar colours. It is typically used as a preliminary test or in conjunction with other analytical methods for a more comprehensive identification.

The flame colour emitted is specific to the metal ion salt.

Lithium – Red

Potassium – Lilac

Copper – Apple Green

Sodium – Orange

Strontium – Red

You will need:

• • • Heatproof mats
    • 250ml Borosilicate beakers
    • Distilled water washer bottle / 100ml beaker of distilled water
    • Ethanol (IDA – Industrial Denatured Alcohol) must only be used
    • 100ml beaker to decant alcohol
    • 10ml Measuring Cylinder
    • Disposable pipette
    • Spatula
    • Weighing boat
    • Balance
    • 3g maximum of each metal salt (Strontium Chloride, Copper Chloride, Lithium Chloride, Potassium Chloride, Sodium Chloride – Boric acid can also be used)
    • Metre rule with wooden splint attached.
    • Matches or lighter
    • Safety glasses

Method:

1. Make sure the laboratory is well ventilated.
2. Ensure heatproof mats cover the bench top. And arrange the beakers in spaced out row along them.
3. Add up to 3g of one type of metal salt into a beaker, add 12 drops of distilled water onto the salt.
4. Measure and add 6ml of Ethanol – IDA only should be added onto the salt.
5. Keep Alcohol 2m away from any flame in a capped bottle
6. Do not allow too much time to pass after the alcohol is added before lighting the vapour. Switch the lights off and ensure the room is as dark as possible after lighting to get the best effect of the flames.
7. Light the alcohol vapour with a lit wooden splint on a metre rule, light the beaker furthest away first.
8. DO NOT ADD FURTHER ALCOHOL TO THE BEAKERS!!
9. Let the alcohol in the beakers to burn out and allowing to cool before attempting to handle the beakers.
10. The remaining salt in the beakers can be used again for future demo’s

All health and safety measures are the responsibility of the teacher doing the demonstration. A thorough risk assessment should be carried out and guidance procedures followed. It is suggested that you practice before demonstration in front of a class.

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