Science Summer EDventure: Chromatography 

...and you thought CHROME was just a Google thing!

Chromatography is a long word (science is good like that!) and if you struggle with saying it, it’s “Croam-a-tog-raffy” with the emphasis on the “tog”.  Fortunately, it’s a sight more fun than it sounds!

In your school, chromatography is the technique you use to investigate simple mixtures like ink, but the great news is that it has masses and masses of applications out there in the big wide world.  For example:

  • chromatography is being used to fight Covid-19: it helps to sort out which vaccines work against coronavirus

  • it’s used in forensics (crime investigation): forgeries, blood on clothing, stuff like that

  • it’s used in finding out what chemicals are in different foods and drinks

  • … and loads more things besides!

Basically, chromatography is an amazing scientific technique and your team at EdPlace are keen for you to get in on the fun and so it’s part of your Summer EdVenture – that’s a big “Wooo!”

 

Learning objectives:

  • To understand that chromatography is a scientific technique used to separate different chemicals, like coloured dyes

  • To investigate how the process of chromatography works for separating dyes in felt-tip pens

  • To determine what the results show us about the different pens used

  • To predict whether chromatography will work horizontally as well as vertically

  • To discover whether food dyes can be separated using chromatography

 

Activity 1: Are black felt pens really black?

OK, so if you’ve done any chromatography at school, there’s a good chance you’ve had a go at this, but there’s nothing like sorting it out for yourself, doing your own take on it, so let’s have a go!

The key thing is to get a good set of felt tip pens – we used Giotto Turbo Colour pens because they work really well, but there are loads of different makes out there.

Here’s what you need:

  • Kitchen towel or coffee filter paper

  • Scissors (careful!)

  • Set of felt-tip pens

  • Several glasses/tumblers with about 1cm of water in the bottom

  • Pencil or biro

 

What to do:

  • Cut out strips of kitchen towel/filter paper about 3cm wide and 15-20cm long

  • Take one of the coloured pens and, on the first strip, put a blob of colour about 2cm up from the bottom

  • Use your pencil/biro to write the name of the colour (black, red, purple, whatever) at the top (or bottom) of your strip so you know what colour you used

  • Place the strip of paper into the glass of water so that it just touches the bottom, with the blob of colour just above the water, and hook the top of the paper over the top of the glass

  • Do the same with the other strips and colours for as many glasses as you have available

  • Wait to see what happens – once the water has reached the top of the glass, take the strip out and leave it to dry. Meanwhile, you can do the same with any of the other colours you haven’t tried yet

  • Now take a look at each strip – what do you see?

 

If your chromatography technique has worked well, your blobs of colour should have spread up the paper and, in some cases, will have separated into different colours. So…

  • Was your black ink just black or were different colours mixed together to make black?

  • Was your purple pen a mixture of red and blue or was it made with a purple dye?

  • What would you predict your orange pen would be made of? Were you right?

Another thing you can do is to line up all your inky pieces of paper (they’re actually called Chromatograms now!) and see whether you can spot the same coloured dye being used in different pens – for example, maybe there’s a yellow dye in the orange pen and in the yellow pen that have travelled up the paper to the same height.

 

What’s going on?

Basically, it’s a tug-of-war!  It’s a battle between the water taking the dyes up the paper and the paper trying to hold on to them as they soak in.  The distance each dye travels will be determined by how well it dissolves in water (or how soluble it is).  So, two yellow dye blobs that travel to the same height in, say, the yellow pen and the orange pen are the same dye – just used in different pens.  Make sense?

 

Activity 2: Will Chromatography work another way?

 

OK, so what you did in activity 1 is called Vertical Chromatography – see if you can work out why!

So, will it work horizontally too?  Let’s check it out.  You could use the same coloured pens, but how about trying something different.  You have a choice here – whatever’s easiest to find.  So, get these together:

  • Kitchen towel or coffee filter paper

  • Coloured sprinkles (like 100s & 1000s) or hard coloured sweets (like Smarties, M&Ms, Skittles, etc.)

  • Small bowls or saucers

  • Water in a small jug

  • Pencil or biro

 

Right – here’s what to do:

  • Set out your bowls/saucers and lay a piece of kitchen towel or coffee filter paper on top.

  • You want ONE colour per piece of paper, so place a brown smartie on one, a blue smartie on another and so on.  Or, if you’re using sprinkles, pour a little on to the surface and separate them into piles of different-coloured strands/balls.  Place a pinch of one colour on to one paper, a pinch of a different colour on to the next and so on.

  • Next, use your pencil or biro to write on to the paper what colour sweet stuff is on it.

  • Now, dribble a little water on to the sweetie thing, so that the colour begins to dissolve and spread across the paper – you don’t want to swamp it!

  • Watch what happens!

 

Now, with the coloured pens, you hopefully saw that vertical chromatography separated some pen dyes into their different colours: it started as a mixture and the water separated them.

You’ve now tried it horizontally, using food dyes.  Did you find out whether it worked?  Are any food dyes mixed together to make a particular colour?

Maybe you can use your results from this investigation to make a beautiful artwork to stick up on your bedroom wall!

 

So, let's recap those learning objectives - how many do you think you've achieved? 

  • Have you been able to see chromatography separating what seemed to be a single colour into its different dyes?

  • Have you been able to see how felt-tip colours are made – were any of the same coloured dyes used in different pens?

  • Have you been able to make chromatography work both horizontally as well as vertically?

  • Have you been able to separate food dyes and see what the manufacturer has used to make a particular colour?

  • Great! Well done and hope that was lots of fun!  There are loads of great resources online to check out.

 

Now, the fun doesn’t have to stop there – your friends at EdPlace have another activity to try out, so why not have a look?

Try our chromatography worksheets for free