pHYSICAL cHEMISTRY - v

Experiment 5

Aim of the Experiment

Separation of given sample using Paper Chromatography.

Principle

Chromatography is a separation technique used to separate the different components in a liquid mixture. It was introduced by a Russian Scientist Michael Tswett. Chromatography involves the sample being dissolved in a particular solvent called mobile phase. The mobile phase may be a gas or liquid. The mobile phase is then passed through another phase called stationary phase. The stationary phase may be a solid packed in a glass plate or a piece of chromatography paper.

The various components of the mixture travel at different speeds, causing them to separate. There are different types of chromatographic techniques such as column chromatography, TLC, paper chromatography, and gas chromatography.

Paper chromatography is one of the important chromatographic methods. Paper chromatography uses paper as the stationary phase and a liquid solvent as the mobile phase. In paper chromatography, the sample is placed on a spot on the paper and the paper is carefully dipped into a solvent. The solvent rises up the paper due to capillary action and the components of the mixture rise up at different rates and thus are separated from one another.

Applications:

• To separate colors in a dye.

• To separate pigments from natural colors.

• To separate drugs from blood.

Materials required

Procedure

• Take a Whatman filter paper strip and draw a line with a pencil above 1-2 cm from one end. Now, draw another line lengthwise from the centre of the paper. Then name the point at which the two lines intersect as P.

• With the help of a fine capillary tube, put a drop of the mixture of red and blue inks at the point P. Let it dry in air.

• Put another drop on the same spot and dry again, so that the spot is rich in mixture.

• Pour equal amounts of isopropyl alcohol and distilled water into a chromatographic chamber and mix it well using a glass rod. It is used as the solvent.

• Suspend the filter paper vertically in the chromatographic chamber containing solvent in such a way that the pencil line remains about 2cm above the solvent level.

• Close the jar with its lid and keep it undisturbed.

• Notice the rising solvent along with the red and blue inks. After the solvent has risen about 15 cm, you will notice two different spots of blue and red colors on the filter paper.

• Take the filter paper out of the jar and mark the distance that the solvent has risen on the paper with a pencil. This is called the solvent front.

• Dry the filter paper and put pencil marks on the centre of red and blue ink spots.

• Measure the distance of the two spots from the original line and the distance of the solvent from the original line.

• Calculate the Rf values of red and blue inks by using the formula.

Observation Table

Calculation

• R_f value of red ink = Distance travelled by red ink from base line divided by Distance travelled by solvent from base line

• R_f value of blue ink = Distance travelled by blue ink from base line divided by Distance travelled by solvent from base line

Result

• R_f value of red ink = ……………

• R_f value of blue ink = …………..

Precautions

• Use the glass ware carefully.

• Use gloves while handling chemicals.

• Carefully suspend the filter paper in the chromatographic chamber containing solvent in such a way that the pencil line remains about 2cm above the solvent level.

• Always close the lid on chromatographic chamber so that the chamber is saturated with the solvent vapors.

Questions

1.Give the name of different separation techniques for a mixture.

2.What is the principle of Chromatography.

References

1. Practical Physical Chemistry by J.B.YADAV