Lesson 9: Separation Techniques

Locating agents :

-chemical reaction/physical process
-colour
-temporary
-> thats why when the colors start to appear, we should quickly use a pencil to outline the spots.

Why pencil?
This is because the pencil mark will not break down and spread out as a dye, like an ink pen would.

Rf value:
distance travelled by spot
distance travelled by solvent

*Note! Rf must be in decimal, not fraction

What factors could affect the Rf value of a chemical?
-Adsorption
-High Solubility
-Choice of Solvent
-Choice of Stationary Phase
-Temperature

How is an Rf value useful?
We can compare Rf values of an unknown sample with Rf values of a known sample.

Chromatography is a system because it has certain fixed elements needed to be present such as, a solvent, a chromatography paper and a mixture. It also has certain rules needed to be followed and carried out so that the system can function.

Lesson 8: Separation Techniques

Chromatography:

















If dye spots are colorless, use locating agent.
Some common locating agents are:
-ninhydrin
-iodine
-UV light (locating method)
-etc.


The 4 main Methods of separation are:
-Crystallisation
-Fractional Distillation
-Simple Distillation
-Filtration

Lesson 7: Separation Techniques

CHROMATOGRAPHY:

The solvent is the mobile phase and the chromatography paper is the stationary phase.

Adsorption - the property of how well a substance in the mixture sticks to the chromatographic column. The higher the adsorption the slower the substance will move along the column.

Solubility - the property of how well a substance in the mixture dissolves into the solvent. The higher the solubility the faster the substance will move along the column.

This is how it looks like:

This how fractional distillation looks like:

Lesson 6: Separation Techniques

Today watched/did :

-Distillation

-Crystallisation

Distillation happened like this:

My Crystals i made with Yi Xue! :D

How to crystalise:

1. Boil water

2. Add copper sulphate and stir till it dissolves

3. Keep adding till it doesn't dissolve anymore( this is its saturation point)

4. Decant it

5. Heat till half of the solvent is boiled

6. Leave to cool and crystals will form

MUAHAHAHA SO FUNNN GAHAHAHA

Lesson 5: Separation Techniques

FILTRATION:

=> separation of insoluble solids and liquids      *soluble means can be dissolved in water

HEATING TO DRYNESS/ EVAPORATION:

eg. salt water => heated to dryness => salt

However, some compounds decompose when heated to dryness!

eg. sugar=>carbon

CRYSTALLISATION:

=> Collect pure solid(soluble) * if solid is thermally unstable, it must be heated indirectly

Saturation

-->When no more sugar can be dissolved

--> changes as temperature changes

*Table Salt CANNOT be crystallised*

Lesson 4: Elements, Compounds and Mixture

Atoms--> monoatomic elements
 eg. He, Ne, Ar, Kr, Xe

*Metals are formed by lattice, while non-metals are formed by molecules

Lattice:

2 elements of the same type combined together, is still an element! :D

Lesson 3: Elements, Compounds and Mixtures

Today, I learnt
-the parts of a bunsen burner
-how to light a bunsen burner
-how to find out which point/region of the bunsen flame is the hottest

Air holes- to allow air to enter the burner
Barrel- (where gas and air are mixed) To raise the flame to a suitable height for heating/burning
Base- to support the pruner and make it more stable
Collar- To control the amount of air entering the burner
Gas Intake Tube- To allow the gas from the gas supply to rush into the burner
Gas tap- To control the amount of gas supplied to the burner

Remember to wear safety goggles before you light the bunsen burner!


How to:

Step 1: Attach the gas intake tube (rubber tube) to the gas tap
Step 2: Close the air hole by adjusting/turning the collar
Step 3: Have the lighter ready; positioned at the top of the barrel
Step 4: Turn the gas tap on completely and strike the lighter immediately and continuously if the burner is not lit. (But if it is not lit after 6 times of striking, off the gas tap and wait for awhile before trying again)
Step 5: Turn the gas tap until the flame is about 5cm tall.
Step 6: Adjust/turn the collar until the air-hole is half opened


From the experiment, I have learnt that the outer yellow cone is the hottest region of the bunsen flame :D

*Always use the glass rod when mixing liquids. Using other instruments could contaminate it.

*Even if a chemical is unused, once it has been taken out of the container, do not put it back. It could contaminate those in the container.