Chromatography

UNDERSTANDING YOUR FOOD<br /> the ultimate educational resource<br /> TEACHER NOTES<br /> <br /> teachers’ notes C3.1<br /> C3. Using chromatography to analyse the colours in<br /> jelly babies<br /> Pupils use chromatography to investigate the composition of the colours<br /> extracted from jelly babies in activity C2.<br /> KS3 and 4<br /> science(possibly technology, but<br /> access to laboratory facilities is<br /> advised)<br /> Timing - 60 - 70 minutes<br /> SAFETY NOTE AND TECHNICIANS NOTES:<br /> TOPREPARE DILUTE AMMONIA SOLUTION; DILUTE ONE<br /> PARTCONCENTRATED AMMONIUM HYDROXIDE R.D. 0.880<br /> WITH 99 PARTS WATER.<br /> THE CONCENTRATED AMMONIUM HYDROXIDE IS<br /> CORROSIVE WITH A HARMFUL VAPOUR; YOU MUST USE<br /> SAFETY GOGGLES; MIXING MUST BE DONE IN A FUME<br /> CUPBOARD.<br /> ABOUT 20 CM<br /> 3<br /> OF DILUTE AMMONIA SOLUTION IS NEEDED<br /> FOR EACH COLOUR REMOVAL.<br /> USE THE DILUTE AMMONIA SOLUTION IN A WELL<br /> VENTILATED ROOM.<br /> Two pupil activity sheets C3<br /> accompany this activity.<br /> Requirements<br /> For removing the dye from the<br /> wool:<br /> • lengths of dyed wool made in<br /> C2<br /> • dilute ammonia solution (see<br /> box)<br /> • 50 cm<br /> 3or 100 cm<br /> 3beakers<br /> • stirring rods or tongs<br /> • hot plates or water baths<br /> • stopclocks<br /> • safety goggles<br /> Safety notes and hints for pupils<br /> Care must be taken when heating the coloured solution to evaporate the<br /> liquid. It is easy to heat the solution to dryness. Pupils must be aware<br /> that even when they stop heating the solution, evaporation continues to<br /> occur.<br /> Heating ammonia solution may produce potentially dangerous fumes.<br /> It is advisable to use the finest tubing as possible to spot the liquids<br /> onto the chromatography paper.<br /> There are a number of waiting times in this experiment and it is advisable<br /> to have activities such as preparing the chromatography paper or others<br /> to occupy the pupils.<br /> The results will obviously depend on the sweets used. Tesco’s own<br /> brand give good results.<br /> For chromatography:<br /> • chromatography or filter paper (if<br /> single chromatograms are to be<br /> run this needs to be about 12 cm<br /> x 3 cm; if you would like to test<br /> all the colours at the same time,<br /> then appropriately larger pieces<br /> are needed)<br /> • solvent - dilute ammonia solution<br /> (see box) volume required will<br /> depend upon the containers you<br /> use as chromatography tanks (use<br /> the ammonia solution in a well<br /> ventilated room)<br /> • melting point tubes or similar<br /> for spotting the coloured<br /> liquids<br /> • beakers, or similar, of a suitable<br /> size to act as chromatography<br /> tanks<br /> <br /> pupil activity C3 CHROMATOGRAPHY<br /> Investigation: Using CHROMATOGRAPHY to separate the mixtures of<br /> colours in jelly babies<br /> SAFETY NOTE<br /> DO NOT EAT ANY OF THE SUBSTANCES USED IN THIS INVESTIGATION.<br /> YOU WILL BE USING DILUTE ACIDS AND ALKALIS; WASH OFF ANY<br /> SPLASHES WITH PLENTY OF WATER.<br /> TELL YOUR TEACHER WHAT HAS HAPPENED.<br /> REMEMBER TO WEAR GOGGLES<br /> Chromatographyis an important method which is used toseparatethe different<br /> components inmixtures.Paper chromatographyis one of the easiest techniquesto<br /> carry out.<br /> The substances that are used to colour food products are often mixtures of two or<br /> more chemicals. In this investigation you are going to find out the colours in the<br /> mixtures used to colour sweets.<br /> Read the safety note before you begin.<br /> Method to extract coloured liquid<br /> 1.You will need a 50 cm wool sample (from investigation C2), on which colours<br /> from jelly babies are ‘stored’.<br /> 2.Place the sample of dyed wool in a smallbeaker. Add just enough dilute<br /> ammonia solutionto cover the dyed wool.<br /> 3.Warm this mixturecarefullyfor 5-10 minutes. You will notice that the ammonia<br /> solution becomes coloured. The wool will lose most of its colour.<br /> 4.Remove the wool so that you are left with just the coloured solution.<br /> 5.Continue to heat the solution so that most, but not all, of the liquid evaporates.<br /> Be careful not to heat to complete dryness. You must obtain a small amount of<br /> a very concentrated liquid. You will use this liquid for chromatography.<br /> 6.Repeat this process for as many colours as you can.<br /> Chromatography of the coloured liquid<br /> 1.Cut the chromatography paper into strips of<br /> about 12 cm x 3 cm.<br /> 2. Dip a very fine piece of glass tubing into the<br /> concentrated coloured liquid.<br /> 3.Spot this liquid onto your piece of chromatography<br /> paper about 15 mm from the bottom of the paper.<br /> 4.Allow the spot todry. Then apply another spot on<br /> top of the first. Do this at least 5 times so that a<br /> darkly coloured, but small, spot is left on the paper.<br /> 5.Pour the dilute ammonia solution into the<br /> container for the chromatogram to a depth of<br /> 3 mm. (The depth of solution must be such that<br /> it isbelowthe level of the coloured spot on the<br /> chromatography paper.)<br /> Handle the paper aslittle<br /> as possible.<br /> Rest it on a clean<br /> surface. This piece of<br /> paper is big enough to<br /> investigate only one of<br /> the coloured liquids. You<br /> may decide to use a<br /> larger piece and<br /> investigate all of the<br /> colours at the same<br /> time.<br /> Continued on next sheet<br /> <br /> CHROMATOGRAPHY pupil activity C3<br /> 6.Place your chromatography paper with the coloured spot into the solventas<br /> shown in the diagram.<br /> 7.The solvent will rise up the paper and carry the different colours different<br /> distances. This will only take a few minutes.<br /> paper clips<br /> splint<br /> Chromatography<br /> paper<br /> Dilute ammonia<br /> solution<br /> Small, dark spot of colour<br /> from jelly babies