Lab: Separation of a Mixture by Paper Chromatography

In this lab, we learned how to use paper chromatography to separate different components of a mixture.

The mixture we used was food coloring.

[Procedure Flowchart]

Part One

l        Prepare three large test tubes and place them in three Erlenmeyer flasks. Label the test tubes A, B, and C.

l        Cut a 66cm chromatography paper into three (each 22 cm). Use a pencil to draw a lien across each strip 4 cm from one end. Cut this end into a point.

l        Place 2 cm deep water in each test tube.

Part Two

l        Use a glass stirring rod and spot the strip of paper with the color assigned. (The spot should be smaller than 0.5 cm in diameter)

l        Insert the strip in test tube A. Observe what happens to the sample spot as the water slowly moves up.

l        Identify the solute front and solvent front. After about 20 minutes, when no further separation of color will occur, remove the stripe. Immediately draw a pencil line across the top edge of the solvent front before it disappears.

l        Measure d1 and d2, record in Tables 1 and 2. Calculate the Rf value and record it as well.

l        Clean up.

Part Three

l        Take the second strip of paper and spot it with a sample of green food coloring. Spot the third strip with a sample of the unknown mixture of food colorings. Label them at the top.

l        Insert the strips in test tubes B and C. Follow the same procedures as in Part Two.

l        Record data in Table 3

l        Clean up.

Oct 17--Separation Techniques

Separating Mixture

How do you separate different components in a mixture?

- by discriminating between components with different properties.

l        high / low density

l        volatile / nonvolatile

l        reactive/ inert

l        soluble / insoluble

l        magnetic / non magnetic

Note: Separation works because components in a mixture retain their identities. However, it would be more difficult to separate if the properties are similar.

²       Filtration: select components by particle size

²       Floatation: select components by density

²       Crystallization and Extraction: select components by solubility

²       Distillation: select components by boiling point

²       Chromatography: select components by

Hand Separation (solids + solids)

- a mechanical mixture or heterogeneous mixture

- can be separated by using a magnet or sieve

Evaporation (solid dissolved in liquid solution)

- boil until the liquid evaporates

- solid part remains

Filtration [solids(not dissolved) and liquids]

- separate by passing the mixture through a porous filter

- use filter paper, the residue is left in the paper while filtrate goes through

Cystallization (solid in liquid)

- precipitation is the conversion of a solute to solid form by physical or   chemical change

-solid separated by 1. filtration

            2. floatation

-saturated solution of a desired solid

-solid come out as pure crystals, then crystals are separated from the remaining  solvent by filtration

Gravity separation

-solid based on different density

-a centrifuge whirls the test tube around at  high speed, which forces the denser  materials to the bottom

*small volumes works better

Solvent extration

-a component moves into a solvent shaken with the mixture

-solvents that dissolve only one component works better

-mechanical mixture (solid in solid) : use liquid to dissolve one solid , then you get the other one

-solution: solvent dissolves one and leaves unwanted solid behind

Distillation (liquid in liquid)

- heating cause low-boiling component to vaporize first

-collecting and condensing  volatilized component 

(Vapour ascents to distillation flask and enters condenser)

Chromatography
-The material of the mixture retains some components, different components flow over the material have different speeds.

- A mobile phase sweeps the sample over a stationary phase.

-This can separate very complex mixtures and  form of separation uses very small sample sizes and analysis is highly accurate and precise.

Sheet Chromatography

Paper Chromatography  (PC) :

-Stationary phase (absorbent) is a liquid soaked into a stripe of paper, mobile phase is a liquid solvent.
-different components move at a different speeds. Some components spend more time in the stationary phase. The components appear as separated spots on the paper.

Thin Layer Chromatography (TLC) :

-stationary phase (ex. Al2O3, SiO2) is a thin layer of absorbent.
-some components bond to the absorbent strongly, some weakly. ( the speeds of the components)

Oct.13--Naming Acids

Compounds with hydrogen ions and a negatively charged ion can form acids when dissolved in water. At the same time, ions are separated from each other.

* H⁺ ion joins with H₂O to from H₃O⁺ (hydronium ion)

 For example, HCl (g) + H₂O (l) à H₃O⁺ (aq) + Cl^- (aq)

How To Name Simple Acids:

1. Use “hydro” as the beginning.

2. Last syllable of the non metal is dropped and replaced with “-ic”.

3. Add “acid” at the end.

( _ide = hydro_ ic acid )

For example: HF = hydrofluoric acid

                        H2S = hydrosulphuric acid

How To Name Complex Acids:

1. change “-ate” into “-ic

change “-ite” into “-ious”

2. Add “acid” at the end of the name

Still confused? Here's a  Youtube video for you!