Expert: Amy - 10/24/2004

Question
Hi,
:)

my question is:

What is chromatography and what are use of it...

can u explain this to me using simple words

(grade 7 student)

thnx in advance
please reply soon  

Answer
Hi,
chromatrography is a way of separating mixtures of different chemicals. For example, pen inks are often made up of a range of different colours.

It's important that the chemicals in the mixture have different chemical properties like size or different abilities to dissolve in different kinds of solutions.


You use these different chemical properties to separate the mixtures.

Here's a simple chromatography experiment.

I've put an explanation of what's happening at the ned of the experiment.

Materials
• Paper coffee filters
• One black • Black water soluble pens
• Container full of water
• Several sheets of paper
• Small glasses or plastic containers
• Isopropyl rubbing alcohol*
• Pencils
• Tape
• Scissors
• Stapler

*Read and obey warnings on rubbing alcohol label.


Instructions

Part I - Separating Black Ink
1. Cut several coffee filters into long strips, one strip per pen.
2. Fold the end of each strip over then staple it to form a loop.
3. Place a dot of ink near the bottom of each strip. Use a pencil to identify which strip belongs to which pen.


4. Poke a pencil through one of the loops you just made. Use the pencil to suspend the strip in a small glass or container.
5. Carefully add water to the glass until it reaches the bottom of the paper strip just below the ink dot. Be sure the ink stays above the water and the paper stays in the water.
6. Allow the water to soak up the strip and watch what happens to the ink drop.
7. If the ink you are testing does not spread out, re-test it using rubbing alcohol.
8. Repeat this process for each strip and compare your results.
9. Let the strips dry and tape them on a sheet of paper as a record of the different pen types.


Part 2- Secret Note Challenge
1. Turn your back while someone uses one of the pens you just tested to write a secret note on a piece of coffee filter.
2. Cut out several individual letters from the note.
3. Staple each letter to the bottom of a strip of coffee filter.
4. Conduct the chromatography experiment above to determine which pen was used to write the secret note.

(Watch how the ink spreads up the paper. Compare it to your known samples of ink.)



What's Happening
The different molecules in the ink have different characteristics such as size and solubility. Solubility is their ability to dissolve in different fluids such as water or nail polish remover. The fluids that the molecules dissolve in are called solvents.

Because of the different characteristcs of the molecules in the ink, they travel at different speeds when pulled along a piece of paper by a solvent (in this case, water).

For example, black ink contains several colours. When the water flows through a word written in black, the molecules of each one of the colours behave differently, resulting in a sort of “rainbow” effect.

Many common inks are water soluble and spread apart into the component dyes using water as a solvent. If the ink you are testing does not spread out using water, it may be “permanent” ink. In such cases, you will have to use a different solvent such as rubbing alcohol.

I hope this information helps. Please write back if you have any more questions.

Cheers,
Amy