Separation Techniques part 3

Olawunmi Omosanya - Wed, 26th June, 2019 @ 06:14: AM

Topics in Chemistry

Salts and Types of Salt in Chemistry Separation Techniques Separation Techniques part 2 Separation Techniques part 3 Physical Change, Chemical Change, Element, Compound and Mixture Electrolysis, Electrolyte, Electrode, Anode and Cathode Grahams law of diffusion Physical Properties of Metals Daltons Atomic Theory and its Modifications Periodic table and Classification of Elements

Academic Questions in Chemistry

The only metal that exist as liquid at room temperature is _____.

  1. Nickel
  2. Duralumin
  3. Mercury
  4. Lead
  5. Titanium
  6. Cesium

ANSWER is Mercury

Mercury is a liquid metal at room temperature. Its chemical symbol is Hg. The name mercury comes from its Greek name, hydrargyrum, which means "liquid silver" .  Mercury has an atomic number of 80. Please read on the periodic table of elements here

The element mercury is also considered to be named after the fastest-moving planet in the solar system. You can read on solar system here.


Separation Techniques:

Please read part 1 here


(7) Fractional Distillation

Fractional distillation is a method used for separating a mixture that contains more than two miscible liquid; and with a close range of boiling points. A typical example of liquid separated by this method is petroleum or crude oil.

If the difference in boiling point is greater than 250C, a simple distillation should be used.

Crude oil contains various fractions and these can be separated via fractional distillation. The fractions are listed below from the most volatile to the least volatile:

  • Fuel gas (most volatile)
  • LPG
  • Refinery gas
  • Gasoline
  • Petrol
  • Naphtha
  • Paraffin
  • Kerosene
  • Diesel oil 
  • Gas oil
  • Fuel oil
  • Lubricating oils
  • Wax
  • Bitumen (least volatile)

Image Credit: Gradeup School

An important apparatus that makes fractional distillation possible is the fractionating column

On heating the mixture (e.g crude oil), the vapours move into the fractionating column (since their boiling points are of a close range). The fractions with a high molecular mass have higher boiling points and condense at lower portions of the column while fractions with lower molecular mass rise to the top of the column to condense. The fraction with lower boiling point (less molecular mass and more volatile) distills into the condenser and is collected as the first distillate. The other liquids with a higher boiling are also collected in a similar way. Please read on molecular mass and molar mass here.


(8) Precipitation

Precipitation is a method used to separate ions in aqueous solution.

Consider an aqueous solution as one that contains water as its solvent

Now, if two ions are present in an aqueous solution, let’s say copper ions (Cu2+) and silver ions (Ag+); one of the ions can be precipitated out if we added another solvent (for instance hydrochloric acid *HCl*)  into the aqueous solution.

On addition of HCl in the above instance, silver ions (Ag+) will be precipitated out of the aqueous solution as silver chloride (AgCl) while the copper ions (Cu2+) will still remain in the aqueous solution.

Ag+(aq) + Cu2+(aq) + Cl-(aq) -> AgCl(s) + Cu2+(aq)

Please read introduction to electrolysis here to get the concept of ions.

Note: The process of precipitation can also be applied in the purification of impure compounds.


Other techniques utilized in the separation of mixtures are:

  • Magnetization

Magnetic separation is used to separate substances that attracted to magnets from those that don’t.

A mixture of iron filings and sulphur can be separated via magnetization.


  • Crystallization

Crystallization is a separation technique used for separating two salts with different solubilities.

It is also used for the purification of a soluble salt that contains insoluble solid impurities.


  • Chromatography

It is used to separate components of a complex mixture in solution, for instance ink.

Below are some types of chromatography:
  • Paper chromatography
  • Column chromatography
  • Gas chromatography
  • Thin layer chromatography

Please read part 2 here

Amazing facts in Chemistry

Gold and copper are the only two non-silvery colored metals. Please read some interesting facts about gold here

Copper is the only metal that is naturally antibacterial. This is why you would see some children carry copper water bottles to school

Water actually freezes faster when it’s warm than when it’s cold

Most element in their pure state exists physically in different forms. For instance, pure carbon can exist as both diamond and graphite. This phenomenon is called allotropy.
Please read on modification of Dalton's atomic theory here.

If you pour a handful of salt into a full glass of water, the water level will go down rather than overflowing the glass.

Similarly, if you mix half liter of water and half litre of alcohol, the total volume of the liquid will be les than one litre


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