Hi and welcome back to freesciencelessons.co.uk. By the end of this video you should be able to describe how to use flame tests to identify five different metal ions. You should then be able to describe flame emission spectroscopy.
This is for triple chemistry students only. Now scientists often need to identify unknown compounds. and many of these contain a metal ion. One way of identifying a metal ion is to use a flame test and we're looking at that in this video. First we place a small amount of our chemical onto wire mounted in a handle.
We then place the end of this into a blue Bunsen burner flame. The colour of the flame can be used to work out the metal ion present. Now it's really important that you learn the colours of the flame tests.
There are five different ones that you need to learn. Okay This shows you the flame test for the lithium ion. Lithium produces a crimson flame test, and that's the word you're expected to use in your exam. This shows the test for the sodium ion.
In the case of sodium, we get a yellow flame. I'm showing you the flame test for the potassium ion here. As you can see, the potassium ion produces a lilac flame. This shows the flame test for the calcium ion. Calcium produces an orange-red flame.
And again you need to use those words in your exam. Okay the final flame test is for the copper ion. As you can see the copper ion produces a green flame. Now there are several problems with using flame tests to identify metal ions.
The colour of a flame test can be difficult to distinguish. That's especially true if there's only a low concentration of the metal compound. And sometimes a sample contains a mixture of metal ions and that can mask the colour of the flame.
For example, if a sample contains the sodium ion, then the intense yellow colour can mask the colour of any other metal ion present. Now, instead of doing flame tests, scientists often use another technique called flame emission spectroscopy. In flame emission spectroscopy, a sample of the metal ion in solution is placed into a flame.
The light given out is then passed into a machine called a spectroscope. The spectroscope converts the light into a line spectrum like this. The key point here is that the positions of the lines in the spectrum are specific for a given metal ion.
So we can use this to identify the metal ion in the sample. So I'm showing you here the line spectra for both sodium and calcium and we can see that they're very different. Flame emission spectroscopy can also tell us the concentration of the metal ion. and that's because the lines become more intense at a higher concentration.
Now flame emission spectroscopy is an example of an instrumental method. In other words, it's carried out by a machine. There are three main advantages to instrumental methods and you need to learn them. Firstly, instrumental methods are rapid.
For example, we could use flame emission spectroscopy to analyze samples more rapidly than we could using flame tests. Secondly, instrumental methods are sensitive. So, flame emission spectroscopy will work even on a tiny sample of metal compound.
And lastly, instrumental methods are accurate. Flame emission spectroscopy is more likely to identify a metal ion correctly than using a flame test. Remember you'll find plenty of questions on flame tests and flame emission spectroscopy in my revision workbook, and you can get that by clicking on the link above.