How to Demonstrate a Classic Flame Test II

In this video, Paul Cook demonstrates how to perform a classic flame test using a spray bottle. This qualitative analytical technique is employed to identify certain elements present in a sample by observing the characteristic colours produced when the sample is introduced into a flame. In this version, alcohol (IDA/IMS only) is added to a series of spray bottles containing metal salts and boric acid. The vapour is ignited and coloured flames are observed.

When specific elements are heated in a flame, the electrons within their atoms become excited and move to higher energy levels. As these electrons return to their ground state, they emit light at precise wavelengths, corresponding to various colours.

The flame test proves particularly useful for the identification of metal ions in the GCSE Chemistry curriculum, as they typically yield easily distinguishable colours. However, it’s important to note that relying solely on the flame test might not be adequate for definitively identifying all elements, as certain elements may display similar colours. Typically, this test is used as a preliminary screening method or in conjunction with other analytical techniques to achieve 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
    • Empty and thoroughly cleaned spray bottles
    • 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
    • 25ml 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)
    • Bunsen burner.
    • Matches or lighter
    • Safety glasses

Method:

1. 1. The spray bottles can be prepared in advance.
   2. Measure and add up to 3g of one type of metal salt into a beaker, add a few drops of water.
   3. Measure and add 20ml of Ethanol – IDA only should be added onto the salt and mix, then pour into one of the clean dry spray bottles.  Label, as necessary.
   4. Make sure the laboratory is well-ventilated.
   5. Where you plan to carry out the demo cover the bench top with heatproof mats and make sure a gas tap is nearby.
   6. Connect a Bunsen burner.
   7. If presenting to students, ensure they are at least 3m away.
   8. Light the Bunsen burner and leave it on the safety flame.
   9. Switch the lights off and ensure the room is as dark as possible after lighting to get the best effect of the flames.
   10. Wear safety glasses, when spraying try to remember to use the bottles at arm’s length and not directly towards anyone.
   11. The bottles can be kept for future demos but the spray nozzle may need to be flushed, as the salts can block them over time.

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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