Working in a Lab
Part of Chemistry Creations
For the final day of Chemistry Creations, we’re thinking about how chemists figure out answers to their questions – usually “what are these chemicals up to?”
To get us started, have a look at this video from Matt, where he takes a look at a technique called fluorescence".
Lots of techniques in chemistry involve shining light on a sample – in particular shining light of different colours to see which colours are absorbed and which are not – a technique called “spectroscopy”. You can put a number to the colour of light your using – called the wavelength – red light has a longer wavelength and violet light has a shorter wavelength – with the other colours of the rainbow having wavelengths in the middle.
In the video above, Matt uses ultra-violet light – the wavelength there is so short that human eyes can’t see it – not until the sample absorbs it and releases light of a longer wavelength – this is fluorescence.
Instead of light, you can do other things to your chemicals. There is a process called “mass spectrometry” – where molecules are smashed apart as they are fired through electric and magnetic fields. The heavier fragments take a more curved path and so hit different parts of the detector to the lighter fragments. This way you can figure out the mass of the atoms in your sample. Take for example sodium chloride – table salt – by looking at the Periodic Table (see Wednesday’s page) you can find the sodium atoms have atomic weight 29 units and that chlorine is 35.45 units. The sodium atoms will leave one trace on the detector but the chlorine will leave two – one trace for the heavier chlorine-37 and one for the lighter chlorine-35. As well as telling you the elements present, mass spectrometry can tell you the “isotopes” present (chlorine has two common isotopes because of the two different numbers of neutrons possible in the nucleus) – this is very useful when for example putting a date to a sample in geology or archaeology.
A lot of the time though, chemistry is not about pure substances – but about mixtures. There are lots of techniques for separating out mixtures into their different parts. One very useful method is “chromatography” – for separating pigments in inks and dyes. You can try it for yourself! You just need some coloured pens, a pot of water, and some kitchen roll. Follow the instructions carefully and at the end you will have separated out your pens’ inks into their different components. You might be surprised how many different colours go into the mixture of inks to make “black” ink.
This page is part of the Chemistry Creations information.
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