CHE1: CHROMATOGRAPHY

Chromatography

Is plant extract a single substance

Leaves were pounded in monster until they were very tender/soft. Then acetone (po) was added and mixture stirred and the extract was poured into the test tube.

A mark was placed at center of the filter paper and placed on the Petridis. Using the tester pipette, drops of the extract were placed on mark on the filter paper at intervals until a large punch formed on the paper.

Experiment 2

Is black ink a single substance?

In experiment2:

A mark was made at the center of the filter paper; black ink was placed at the center. Using a teats pipette drops of propemone were placed on the ink at intervals until a large punch formed on the filter paper.

Observation

What was the color plant extract?

Light green

What was observed on the filter paper

  • Rings of colors
  • light green
  • purple
  • pink color.

Experiment 2

What color was the ink?

Black

How many colors can you see?

Purple (light)

Black

Grey

Conclusion

This process of separating mixture is called chromatography. The punch is a chromatogram.

How does chromatography work?

A mixture of dyes is separated. The substances with move very fast form the outer most rings on the filter paper and those that move slowest form the inner most ring. There are many rings as there substances in a mixture of dyes.

How to separate a mixture of Iodine and common salt

The mixture in heated in a beaker as follows.

 

heat

Observation

When a mixture was heated, dense purple fumes filled the beaker. Then heating was discontinued and the apparatus was left to cool. Grayish diamond crystals were seen at the bottom of the flask.

Explanation

What color is common salt?

White

What is seen when common salt is heated?

It isn’t affected by heat

What color is iodine?

Grey

When it’s heated?

It forms a purple vapor

What is observed when it is cool?

Grey crystals form at the walls of the test tube.

What substance forms the dense purple fumes?

The Iodine

What was the use of the cold water in the flask?

To cool the purple vapor

The purple vapor formed grey crystals when added

Conclusion

This method of separating two solids in called sublimation.

Sublimation is used to purify Iodine. After separating the mixture, how do you get the purity of the components?

-By finding the melting point of solid and boiling point of liquid

How do you make solid particle in a suspension settled quickly.

For example:

Chalk dust in water.

Use a centrifuge the process can be used in getting cream free milk.

A pure liquid has a definite boiling point at a particular pressure, for example water this morning had a boiling point of impurities on boiling point.

The boiling point experiment was repeated with some salt added to some water and the boiling point of water was 98oc. Therefore impurities raise the boiling point of liquids.

Determining the melting point of a solid the temperature of Naphthalene is 110oc at a time after 30 seconds it is 89oc, another30 seconds, 82oc, and then 80ocfor another 30 seconds, then 79oc.

 

melting point

When determining the melting point of naphthalene

The apparatus was set up as in the diagram.

 

naphanale

Observation

It was not easy to decide which one was the melting point the temperature when the naphthalene starts melting or when half or all of it has melted.

Therefore the naphthalene was left to melt completely and then left to cool. The temperature of the cooling naphthalene was taken at intervals of 30 seconds. A temperature time curve was plotted.

The melting point is the temp that remained constant after a number of times. Therefore the melting point of naphthalene is 80oc.

Do impurities change the melting point of a solid?

The experiment to determine the melting point of naphthalene was repeated with a little oxalic acid added as an impurity.

 

cooling point

From the second cooling curve the melting point of naphthalene is

The melting point is lowered by impurities. The melting point is not sharp. Therefore an impure substance does not have definite melting point and less spoil it.

The video below shows a paper chromatography experiment conducted to separate the different pigments present in a wet erase marker.

ASSIGNMENT : CHROMATOGRAPHY MARKS : 10  DURATION : 1 week, 3 days

 

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