pHYSICAL cHEMISTRY - Iv

Experiment 4

Aim of the Experiment

Identify the inorganic anions CI-, Br- and I- by paper chromatography. (mode: Ascending paper chromatography)

Principle

Chromatography is the technique which is used for separation of constituents of

a mixture. The technique of chromatography is based on adsorption of the

components of a mixture on a suitable adsorbent. It is used for coloured and

colourless both type of mixture.

Materials required

APPARATUS REQUIRED:-

Whatmann filter paper no.1, capillary tube, chromatography jar, lead pencil,

scale.

CHEMICAL REQUIRED:-

i. Inorganic mixture containing CI-, Br- and I- ions.

ii. Developing solvent (10ml of n-butyl alcohol + 5ml pyridine + 10ml 1.5

M NH4OH).

iii. Visualising reagent (ammonical AgNO3 solution)

Procedure

1.First of all cut a strip of about 20 × 5 cm from whatmann filter paper no.1.

2. Now draw a horizontal line with pencil about 2 cm from the bottom.

3. Apply a spot of mixture solution containing CI-, Br- and I- ions on the

pencil line by means of a capillary tube. Dry the spot with the help of air

dryer.

4. Now lower the filter paper strip into chromatography jar in such a way

that it does not touch the sides of the jar and hangs vertically straight.

5. Place the developing liquid i.e. (10ml of n-butyl alcohol + 5ml pyridine +

10ml 1.5 M NH4OH )in the jar and cover it. The level of the solution

should be 2-3 cm only.

6. Allow the developing liquid to rise till it has travelled a distance of about

15cm. then dry the strip with the help of air dryer.

7. After that spray ammonical AgNO3 solution on the filter paper strip when

three spots (two black and other yellow) will appear on the strip.

8. Measure the distance travelled by spots as well as by the solvent.

Observations

Distance travelled by CI- spot = d1cm

Distance travelled by Br- spot = d2cm

Distance travelled by I- spot = d3cm

Distance travelled by solvent front = d4 cm

Calculations

Rf value of CI- = 𝑑1 divided by 𝑑4

Rf value of Br- = 𝑑2 divided by 𝑑4

Rf value of I- = 𝑑3 divided by 𝑑4

Result

Rf value of CI- (chloride) ion =

Rf value of Br- (bromide) ion =

Rf value of I- (iodide) ion =

Precautions:

i. Always keep the glass jar covered and undisturbed during the experiment.

ii. The paper strip should be erect and not curled.

iii. The spots of the solution must not dip in the developing solvent.

iv. Use a fine capillary tube for applying a spot of solution.

Reference Material

1. Practical Physical Chemistry Google EBOOK Link.

Questions

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

2.What is the principle of Chromatography.