chromotography

Chromatography

(from Greek χρώμα:chroma, color and γραφειν:graphein to write) is the collective term for a set of laboratory techniques for the separation of mixtures.

OC2 separate mixtures using chromatography

Chromatography is the separation of a mixture into its constituent parts. Dark Dyes are usually made from different colour dyes. Inks and food colourings are the same. In this section we can use techniques to separate the coloured dyes out of the mixtures because each have different properties.

Chromatography works by separating the individual parts of a mixture so that each one can be analyzed and identified. In the decades since its invention, the chromatograph has become an essential piece of equipment in bio-chemical laboratories. Using the analytical technique of chromatography, scientists can tell what chemical compounds are present in complex mixtures. These mixtures include such diverse things as smog, cigarette smoke, petroleum products, or even coffee aroma. Without chromatography, chemists might not have been able to synthesize proteins such as insulin or understand how plants use the sun's energy to make food.

The first chromatograph was invented by Russian botanist Mikhail Semenovich Tsvett (1872-1919). While working in Poland, Tsvett was looking for a method of separating a mixture of plant pigments (tints) which are chemically very similar to each other. To isolate different types of chlorophyll, he trickled a mixture of dissolved pigments through a glass tube packed with calcium carbonate powder. As the solution washed downward, each pigment stuck to the powder with a different degree of strength, creating a series of colored bands. Each band of color represented a different substance. Tsvett referred to the colored bands as a chromatogram. He also suggested that the technique (now called adsorption chromatography) could be used to separate colorless substances.

http://www.discoveriesinmedicine.com/Bar-Cod/Chromatography.html

Chromatography in the Lab

You can separate colours from a dye if you allow it to separate up porous material, using a solvent the dye is soluble in.

Separation of the different dyes in INK

New Version of Experiment

http://resources.schoolscience.co.uk/Salters/pdfs/voltwo/SCC2_Prac14.pdf

OC2 separate mixtures using chromatography

record on time lapse

Apparatus

Chromotography Paper, Coloured Candy sweets, Water, Jar, Elastic Band, weigh boat.

Method

  1. In separate weigh boats separate different colour candy coated sweets.
  2. To these weigh boats add only a few drops of water. Allow them to sit for 5 mins.
  3. Get some chromatography paper about 30cms long,
  4. About 2 cm from one end, draw a line with a Pencil.
  5. Drop some colour from the sweets above this line
  6. Place a little water in a gas jar, about 15ml.
  7. Only the bottom of the strip should touch the water, the ink dot should be above the water.
  8. Allow stand for 15-20 mins, remove from the solvent.
  9. Allow it to dry,
  10. Observe the different dyes that make up the Ink.

The diagram says to suspend it on the glass,

it might be more desirable to hang it from a pencil.

Try both ?

Results

Different colours go up the chromotography paper

Conclusion

Different Food dyes separate at different speeds in water.

If it didn't separate, dry it and repeat the next lesson with alcohol

Keep strip and write up the observation.

Another method, is to do it with sweets,

you know the type of sweets that leave the colours on your hand when they melt.

separate them into groups of the same colour.

Place the same colour sweet on a thin strip of some blotting paper,

add a few drips of water and leave it stand for a while.

Come back and Observe.

do it to the chlorophyll in leaves

http://www.practicalchemistry.org/experiments/chromatography-of-leaves,199,EX.html

Chromatography at Home

No problem doing this at home!

Paper tissue or toilet paper will do.

Draw a circle with a felt tip pen,

drip water slowly into the centre of the circle

and watch the colours separate