Lab session 3

Separation techniques

Today, we did chromatography! (as promised.)

EXPERIMENT TIME!!! XD

Purpose: To separate the dyes in green food colouring

Materials used:

-Capillary tube

-Green food colouring

-Chromatography paper

-Boiling tube

-Pencil

-Ruler

-Distilled water

-Clothes peg

Step 1: Draw a line across the chromatography paper 1.5cm from the edge with a pencil:

Step 2: Using the capillary tube, dot at most 3 drops of Green food coloring on the same spot in the middle of the line. 

Step 3: Fill the boiling tube with distilled water (Just 1.5cm^3 of water will do). 

Step 4: Making sure that there is no water on the sides of the boiling tube touching the chromatography paper, carefully place the chromatography paper into the water, with the water below the pencil line (Use the clothes peg to secure the chromatography paper): 

(Okay, I put more than 1.5cm^3 of water.)

Step 5: Watch the dyes move up! :D (It's really cool)

Step 6: After about 10-15 minutes or so, take out the chromatography paper. Let it dry. I got this:

But most, if not all of my classmates got this:

(I hope I didn't get it wrong. :p)

Mark the solvent front. Now, calculate the Rf values.

What are Rf Values?

Retention Factor (Rf) 

Unknown substances separated by chromatography can be identified by Rf values.

So basically, Rf value = Distance moved by substance / Distance moved by solvent. It should always be less than 1, or else something's wrong.

So... 

Here are my results:

So, yep.

TAKEAWAY FROM LESSON: Paper chromatography separates a mixture of solute with different solubility and degree of adsorption. 

e.g. The more adsorbent the solute, the further up the paper it travels, vice versa. 

!!!!NOTE!!!!

Adsorbent does NOT mean Absorbent. 

Adsorbent: (of a solid) hold (molecules of a gas or liquid or solute) as a thin film on the outside surface or on internal surfaces within the material:charcoal will not adsorb nitrates | the dye is adsorbed onto the fiber.

Absorbent: take in or soak up (energy, or a liquid or other substance) by chemical or physical action, typically gradually: buildings can be designed to absorb and retain heat | steroids are absorbed into the bloodstream. 

(Taken from dictionary)