Chemistry

Mixtures and Separation of Mixtures - part 3

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

Topics in Chemistry

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 Mixtures: Characteristics of Mixtures Physical Properties of Matter explained with Examples Chemical Properties of Matter explained with Examples Differences between Physical and Chemical Change 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 Elements: Characteristics of Elements Salts and Types of Salt in Chemistry Mixtures and Separation of Mixtures Mixtures and Separation of Mixtures - part 2 Mixtures and Separation of Mixtures - part 3


Academic Questions in Chemistry

Please check out our Test Your Knowledge page to see all Questions and Answers

Which of the following is NOT a characteristic of chemical change?

  • A. A new thing is formed
  • B. It cannot be easily separated into it's constituents elements
  • C. A new chemical formula accompanies whatever is formed
  • D. The burning of candle is an example of a chemical change
  • E. Blood is an example of a chemical change
  • F. Iron rust is an example of a chemical change

Which of the following statement is FALSE concerning a physical change _____.

  • A. Substances formed in a physical change have a unique chemical formula and IUPAC name
  • B. It's a change that is easily reversible
  • C. It's a change that can be separated via an appropriate separation technique
  • D. No new substance is formed
  • E. A mixture of salt and water is a physical change
  • F. Physical change can result to a change in color and shapes of substances

The following substances will sublime EXCEPT _____.

  • A. Sodium Cryolite
  • B. Solid Carbon(IV)oxide
  • C. Arsenic
  • D. Sulphur
  • E. Iodine Crystals
  • F. Naphthalene

Which of the following is a state of matter?

  • A. Ions
  • B. Plasma
  • C. Compounds
  • D. Molecules
  • E. Atoms
  • F. None of the above

The ideal way of separating a mixture of blood is through _____.

  • A. Chromatography
  • B. Fractional Distillation
  • C. Centrifugation
  • D. Filtration
  • E. Separating Funnel
  • F. Fractional Crystallization

Which of the following separation technique is used to separate an insoluble solid that sediments in a liquid?

  • A. Crystallization
  • B. Fractional Crystallization
  • C. Sublimation
  • D. Separating Funnel
  • E. Fractional Distillation
  • F. Decantation

A _____ mixture is said to be uniform all through.

  • A. Homogenic
  • B. Heterogenic
  • C. Homogenous
  • D. Heterogenous
  • E. Concentrated
  • F. Diluted

The reaction involving an acid and a base is termed _____.

  • A. Hydrolysis
  • B. Neutralization
  • C. Combustion
  • D. Displacement
  • E. Decomposition
  • F. Sublimation

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Separation of Mixtures:

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

As discussed in the previous articles, a mixture is composed of two or more substances physically combined.

In this article, we will continue with the various separation techniques but if you desire, you can read from the beginning of this topic 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 a mixture separated via fractional distillation is petroleum or crude oil.

Note: 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 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.

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.

Fractional Distillation - Len Academy

Note: Notice that the gases (at the top of the fractionating column and with lower boiling points) 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.

Process of Fractional Distillation

  1. On heating the mixture (crude oil), the vapours move into the fractionating column (since their boiling points are of 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 a pure substance recovered via the process of distillation on 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.

 

(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 or HCl) into the aqueous solution.

Please read on Acids - Their Physical and Chemical Properties here.

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

Note: To "precipitate out" (or simply precipitation) means to bring about the deposition of a substance in its solid form from a solution.

Now, back 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+) will 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 on the Introduction to Electrolysis to get the concept of Ions.

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

Note: 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 substances 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 be 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 crystallization, the less soluble salt is crystallized out of solution.

Please read on Salts and Types of Salt in Chemistry here.

Crystallization 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

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len

Alfred Ajibola is a Medical Biochemist, a passionate Academician with over 7 years of experience, a Versatile Writer, a Web Developer, a Cisco Certified Network Associate and a Cisco CyberOps Associate.


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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. 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


NOTABLE POINTS IN Chemistry