Flame Tests

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Added : 2017-12-11 Views :34K

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Flame Tests




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Presentations text content in Flame Tests

Slide1

Flame TestsLO - To demonstrate flame tests and explain why they work

Slide2

What are we testing to find?

Flame tests are used to identify the cations present in salts.

Cations are the positive ions.

They are the ions of metals, examples being K

+

, Mg

2+

, Al

3+

.

If a cation is present in the sample, the flame will give a distinctive colour.

Slide3

How do we do the test?

Firstly you need a wire loop, a lit bunsen flame, and the sample salt.

The sample may be a powder or a solution.

Heat the loop in the flame before every test to get rid of any residue from previous tests.

Be careful with the loop - it will get hot.

Then place the loop into the sample to collect a bit at the end, and then place the loop at the hottest part of the flame - observe what colour you see.

There is a demonstration video at the end of this presentation.

Slide4

What results might we get?

You might see a number of colours dependent upon the cation present:Lithium Li+ crimsonSodium Na+ yellowPotassium K+ lilacCalcium Ca2+ orange-redCopper Cu2+ green-blue

Slide5

Why does this test work?

When metals are heated energy is transferred to their electrons

This makes the electrons move to higher electron shells

When the electrons move back to their normal electron shells, energy is transferred back to the surroundings as radiation.

We see this radiation as light. Because each metal has different electron arrangements, the energy of the radiation differs.

The light we see as different colours because the light has different frequencies for each metal.

Slide6

Watch this video to see the test in action

https://www.youtube.com/watch?v=1EXr_L7Ojqg

Watch this video to see why flame tests work

https://www.youtube.com/watch?v=ntlO8L5moDw

Slide7

Summary

Flame tests are a method of identifying the cations (positive ions) present in an unknown sample. We make the identification based upon the colour flame we observe.


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