Mixtures and Separation of Mixtures - part 3

len Alfred Ajibola - Wed, 26th June, 2019 @ 06:14 AM

Topics in Chemistry

Avogadro's number explained with worked examples Mole and Avogadro's Number explained Le Chatelier's Principle: Changes in concentration and pressure in dynamic equilibrium Chemical Equilibrium: Dynamic Equilibrium in Chemistry Static and Dynamic Equilibrium explained with their differences Chemistry Scheme of Work, SS1, First Term Chemistry Scheme of Work, SS1, Second Term Chemistry Scheme of Work, SS1, Third Term Compounds in Chemistry: Characteristics of Compounds Types of Mixture: Homogenous and Heterogeneous Mixtures What are mixtures? Characteristics of mixtures Physical properties of matter Chemical properties of matter explained with examples Differences between physical and chemical change in chemistry Ionic Theory and Electrolysis Physical and Chemical Properties of Acids States of Matter: Characteristics of Solids Liquid state of matter: Characteristics of liquids Gaseous state of matter: Characteristics of gases Molar Mass, worked examples and differences with molecular mass

Academic Questions in Chemistry

Please click here to see all Questions and Answers

Which of the following isn't an element of the periodic table.

  • A. J

  • B. Y

  • C. W

  • D. B

  • E. U

  • F. K

According to the periodic table, elements in the same group have got the same number of shells.

  • A. True

  • B. False

The periodic table of elements is also called the Mendeleev's table.

  • A. True

  • B. False

The simplest formula of a compound is termed _____.

  • A. Emperical formula

  • B. Molecular formula

  • C. Avogadro's number

  • D. Mass formula

  • E. Molar mass formula

  • F. Mole ratio

A compound composed of iron (Fe) and oxygen (O) was analyzed and found to contain 69.94% iron and 30.06% oxygen. Find the empirical formula of the compound. (Molar mass of Fe=55.85, O=16)

  • A. FeO

  • B. Fe2O3

  • C. Fe3O4

  • D. FeO2

  • E. Fe3O6

  • F. Fe2O4

Which of the following statement is false concerning hydrocarbons?

  • A. Hydrocarbons can be aromatic

  • B. Hydrocarbons are made up of carbon and hydrogen only

  • C. Alkynes are aliphatic hydrocarbons

  • D. Alkenes have a carbon-carbon double bond in their structure

  • E. Benzene ring has a carbon-carbon triple bond in its structure

  • F. Hydrocarbons are the main constituents of petroleum and natural gas

The ability of carbon to form long chain of itself is called _____.

  • A. Carbon chain reaction

  • B. Catenation

  • C. Carbontion

  • D. Carbontion

  • E. Organic chemistry

  • F. Carbon moleculation

Calculate the relative molecular mass of methane. (Carbon = 12.001, H = 1.00794).

  • A. 13.00894 amu

  • B. 11.00206 amu

  • C. 12.00794 amu

  • D. 14.001 amu

  • E. 15.001 amu

  • F. 16.033 amu

Separation of Mixtures:

The separation of mixtures can be carried out via the appropriate separation technique.

As discussed in a previous article, mixtures are composed of two or more substances physically combined.

In this article, we will continue with the various separation techniques. Meanwhile, it is recommended you read the commencement of this topic here.

Below are other methods through which mixtures are separated.


  • Fractional Distillation

Fractional distillation is a method used for separating mixtures that contains more than two miscible liquid with a close range of boiling points.

A typical example of a mixture separated via fractional distillation is petroleum or crude oil.

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

Crude oil contain various fractions and these can be separated via fractional distillation.

The fractions of crude oil (petroleum) are listed below from the most volatile to the least volatile.

For now, think of a volatile substance as one that has a lesser boiling point and is easily evaporated at normal temperatures.

The fractions of petroleum are:

  • Fuel gas (most volatile)

  • LPG

  • Refinery gas

  • Gasoline

  • Petrol

  • Naphtha

  • Paraffin

  • Kerosene

  • Diesel oil

  • Gas oil

  • Fuel oil

  • Lubricating oils

  • Wax

  • Bitumen (least volatile)

  • Please read on hydrocarbons here.

The image below shows the process of fractional distillation as seen in an industrial environment.

Fractional Distillation - Len Academy

Seen in the image are:

  • A fractionating column containing the fractions of crude oil.
  • The temperature at which the fractions are evaporated.
  • The uses of the respective fractions.

Notice that the gases at the top of the fractionating column have lower boiling points. They are the most volatile while bitumen asphalt (at the bottom) is the least volatile.

The image below shows the process of fractional distillation as seen in a laboratory:

Fractional Distillation - Len Academy

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

The fractionating column functions to separate the mixture (crude oil in our instance) into its fractions or constituents based on the differences in their boiling point and volatilities.

Note: The fractionating column is absent in simple distillation.

You can read on simple distillation here.

Processes of fractional distillation

  1. On heating the mixture (crude oil), the vapours move into the fractionating column since their boiling points are at a close range.
    Please read on the concept of heat and temperature here.
  2. The fractions with higher molecular mass will always have a higher boiling point. They will therefore condense at lower portions of the column. These fractions are less volatile.
  3. The fractions with lower molecular mass rise to the top of the column to condense. The is so because they have lower boiling points and are more volatile.
  4. The fraction with the lowest molecular mass and lowest boiling point (most volatile fraction) distills into the condenser and is collected as the first distillate. A distillate is defined as a pure substance recovered via the process of distillation from a mixture.
  5. The other fractions with higher boiling points are also collected in a similar way.
  6. Please read on molecular mass and molar mass here.


  • Precipitation

Precipitation is a method used to separate ions in aqueous solution. In this instance, a solution is considered to be aqueous if it contains water as its solvent.

As an instance, 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 of solution if we added another solvent like hydrochloric acid or HCl into the aqueous solution.

Please read on acids here.

The precipitated substance or solid (or ion in the above instance) is termed a precipitate.

Meanwhile, understand that the term precipitation means to bring about the deposition of a substance in its solid form from a solution.

With reference to our initial instance, on addition of HCl into the aqueous solution, silver ions (Ag+) will be precipitated out as silver chloride (AgCl) while the copper ions (Cu2+) still remain in the aqueous solution.

Below is the equation for the reaction:

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

Please read the introduction to electrolysis and ions here.

The diagram below shows the precipitation of lead ions (Pb2+) and iodide ions (I-) as lead iodide (PbI2) in the reaction between lead trioxonitrate(V) - Pb(NO3)2 and sodium iodide (NaI2).

Precipitation - Len Academy

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


Other Separation Techniques

Other techniques utilized in the separation of mixtures are:

  • Magnetization

Magnetization or magnetic separation is used to separate solids that are attracted to magnets from those that aren't.

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

The above statement is valid because the iron filings will become attracted to a magnet while sulphur particles remains unattracted inside the container.

Please read on the physical properties of metals here.


  • Crystallization

Crystallization is a separation technique used for separating two salts with different solubilities. In this regard, the less soluble salt is crystallized out of solution.

Please read on salts chemistry here.

Crystallization is also applied in the purification of soluble salts 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:

  1. Paper chromatography
  2. Column chromatography
  3. Gas chromatography
  4. Thin layer chromatography

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Amazing facts in Chemistry

The only letters that failed to appear on the periodic table are letters:

J     &     Q

Gold and copper are the only two non-silvery colored metals.

Copper is the only metal that is naturally antibacterial. For this reason, some children utilize 'copper water bottles' in schools

Water 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

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


In chemistry, hydrocarbons can be classified as either aliphatic or aromatic. Recently, both classifications of hydrocarbon were based on their structure rather than their origin.

Aliphatic hydrocarbons are put into three main groups according to the types of bonds they possess. These are:

  1. Alkanes

  2. Alkenes

  3. Alkynes

They are shown in the image below:

Alkanes, Alkenes and Alkynes - Len Academy

It's important to note the followings:

  • Alkanes have single bonds (only) in their structures.

  • Alkenes always have a carbon-carbon double bond present in their structure.

  • Alkynes always have a carbon-carbon triple bond present in their structure.


Aromatic hydrocarbons are classified into:

  • Arenes: They contain benzene ring as a structural unit. Below is the structure of a benzene ring.

Benzene Ring - Len Academy


  • Nonbenzenoid aromatic hydrocarbons: They possess special stability but lack a benzene ring as a structural unit.

Organic chemistry is the study of carbon and it's compounds.

Carbon is the focus of organic chemistry because it has a wide chemical diversity in the sense that it can combine with other carbon atoms to form a long chain of carbon molecule. This ability and process whereby carbon can form a long chain of itself is called catenation.

Please read the introduction to organic chemistry here

A major challenge encountered when calculating molecular mass is that it becomes difficult or impossible to calculate especially when the relative molecular mass of large molecules, polymers and macromolecules are involved.

Examples of large molecules (with indefinite molecular masses) include carbohydrates, cellulose and complex sugars.

The large molecules (above) have no specific chemical formula throughout their volume.

Please read more on carbohydrates and sugars here

Understand that Relative Molecular Mass prove to be useful only when we calculate substances with small and definite molecular sizes. This was proven through the modifications of Dalton's atomic theory.

Please read on Dalton's atomic theory and its modifications here.

Calculate the Relative Molecular Mass of methane (CH4). (Carbon=12.001 and H=1.00794)

  • Molecular Mass = Atomic mass of carbon + Atomic mass of Hydrogen

  • Methane is composed of one atom of Carbon and 4 atoms of Hydrogen.

  • 12.001 + (1.00794 x 4)

Molecular Mass of Methane = 16.033 amu

Please read more on molecular mass here

Calculate the Relative Molecular Mass of water (H2O). (Oxygen=15.9994 and Hydrogen=1.00794)

  • Molecular Mass = Atomic mass of Hydrogen + Atomic mass of Oxygen

  • Water contains 2 atoms of Hydrogen and 1 atom of oxygen.

  • (1.00794 x 2) + 15.9994

Molecular Mass of Water = 18.015 Da

Please read on emperical formula and its calculations here

Gold - Len Academy

Below are some facts about gold:

  • It is the only metal that has a gold (golden) color

  • Gold is present inside the earth crust in all the seven continents

  • Pure gold is soft and very stretchable (It can even be stretched into threads)

  • The Latin name of Gold is aurum which means 'shining dawn'. For this reason, its chemical symbol is 'Au'

  • Gold is a very good conductor of electricity. This is why it’s sometimes used in making USB and audio cables

  • Gold is non toxic and can be eaten with food. It is sometimes added to desserts in some expensive restaurants

  • The term Gold originated from an ancient English word 'geolu' which means yellow

  • 24karat gold is the purest gold element

Please read more interesting facts about gold here