Chemistry

Mixtures and Separation of Mixtures - part 2

len Alfred Ajibola - Wed, 26th June, 2019 @ 06:15: AM

Topics in Chemistry

Le Chatelier's Principle: Changes in Concentration and Pressure explained 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 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


Academic Questions in Chemistry

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

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

Which of he following is not a fact concerning gold?

  • A. 24 karat gold is the purest gold element

  • B. It is the 50th rarest metal amongst all elements found beneath the earth crust

  • C. It is the most malleable and ductile pure metal ever known

  • D. It is the only metal with a golden color

  • E. Gold is non toxic and can be eaten with food

  • F. It's present inside the earth crust in all seven continents

Which of the following is not an example of a chemical change?

  • A. The burning of wood
  • B. The melting of candle wax
  • C. The decomposition of food
  • D. The rotting of leaves
  • E. The lightening of a match stick
  • F. None of the above

Which of the following is not a fraction of crude oil?

  • A. Gasoline
  • B. Naphtha
  • C. Benzene
  • D. Wax
  • E. Paraffin
  • F. Lubrication Oil

The Separating Funnel is a technique used in the separation of mixtures. Another name for Separating Funnel is the _____ Funnel.

  • A. Partition
  • B. Separatory
  • C. Division
  • D. Liquid
  • E. Half
  • F. Dividing

2NH4+(aq) + Ag+(aq) -> 2H4AgN

The equation above represents _____ acid.

  • A. Svante Arrhenius'

  • B. Brønsted–Lowry's

  • C. Gilbert Lewis'

  • D. Avogadro's

  • E. Sir Isaac Newton's

  • F. Albert Einstein's

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Separation of Mixtures:

Recall that a mixture is made up of two or more substances physically combined.

Please read more on Elements, Compounds and Mixtures here.

In this article we will continue from where we previously stopped. In case you wish to read the Part one of this topic; it's present here.

 

(5) Centrifugation

Centrifugation involves the use of a device called centrifuge to separate the lighter portions of a mixture from the denser portions through the spinning action of the centrifuge.

Note: Blood is a mixture and its components can be separated via centrifugation.

Blood is considered a mixture because it is composed of liquid plasma and solid cells.

Please read on the Red Blood Cells here.

Below is an image of separated blood components via the process of centrifugation.

Centrifugation - Len Academy

Using the above diagram as a reference, the test tubes containing the blood are inserted into the centrifuge.

The centrifuge begins to spin/rotate when it's switched on; and this is allowed to continue for about 5 to 10 minutes.

On bringing out the test tubes from the centrifuge, two different layers will be observed. These are:

  • The lower layer composed of solid cells that had sedimented.
  • The upper layer containing the plasma will be seen above it.

Next, the plasma can then be carefully decanted from the test tube. (Please see sedimentation and decantation in the part 1 of this article).

Types of Centrifugation

Below are some of the types of centrifugation:

  • Differential Pelleting or Differential Centrifugation
  • Isopynic Centrifugation
  • Density Gradient Centrifugation
  • Rate-Zonal Density-Gradient Centrifugation

 

(6) Sublimation

Matter exists in 4 states. These are:

On heating a solid, it changes to liquid. If we continue heating, the liquid will eventually change to gas. This is the usual sequence.

However, in sublimation, the heated solid does not pass through the liquid phase; instead, it changes to gas directly.

Sublimation can be defined as a process whereby a heated solid changes directly to gas without passing through the liquid phase.

A sublimate is a substance that changes directly from solid to gas or from gas to solid.

Such solids are said to sublime.

The diagram below shows sublimation via a solid that sublimes. (Ammonium Chloride or NH4Cl):

Sublimation - Len Academy

Examples of solids that sublime are:

  • Ammonium Chloride (NH4Cl)
  • Iodine Crystals
  • Sulphur
  • Solid Carbon(IV)oxide (CO2) or Dry Ice
  • Arsenic
  • Naphthalene

Sublimation is used to separate two salts (or solids) in which one sublimes and the other does not.

An an instance, a mixture of common salt (NaCl) and iodine crystals (I) can be separated via sublimation.

On heating, NaCl remains in the heated dish or container while the iodine crystals sublimes; (that is; it changes into a gas and may be collected afterwards as the sublimate).

Please read on Salts and Types of Salt here.

 

(7) Distillation

Distillation is a technique used to separate two or more miscible liquid that have different boiling points.

Note: The boiling points of the different liquids are not usually at a close range.

Think of miscible liquids as two or more liquids that can dissolve in each other (or one another).

The mixture of water and ethanol is a typical example of a mixture that can be separated via distillation. This is so because they are both miscible and have different boiling points.

The mixture of water and acetone are also miscible and can be separated via distillation.

  • Water boils at 100oC
  • Ethanol boils at 78oC

The image below shows the separation of water and ethanol via distillation:

Distillation - Len Academy

Steps involved in Distillation

  1. To carry out distillation, the mixtures of both liquids are heated in a tube until the one with a lower boiling point (ethanol in our instance) vapourizes or changes to vapour at 78oC.
    Please read on the Concept of Heat and Temperature here.
  2. The vapour is collected and cooled by passing it through a condenser.
  3. The condenser compresses the vapour (gaseous ethanol) into liquid.
    Please read on the Parts of a Refrigerator and how they Operate here.
  4. The ethanol is collected; and is referred to as the distillate.
  5. The water remains in the heated tube since its boiling point is 100oC.

Think of a distillate as a liquid collected from the process of distillation after it has been passed through a condenser.

When we have two liquids of different boiling points; the liquid with a lesser boiling point is said to be more volatile while that with a higher boiling point is said to be less volatile

Distillation can also be used to:

  • Separate a Solid and a Liquid: The evaporated liquid is collected and condensed while the solid remains in the container.
  • Purify Liquid: This is true since only the pure liquid will vapourize leaving behind the solid impurities in the container.

Please read on the Separation of Mixtures - Part 3 here.

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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 utilize 'copper' water bottles in schools

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

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

An acid is a substance that produces Hydrogen ions (H+) when dissolved in water (or when in the form of an aqueous solution).

Svante Arrhenius definition of Acid

 

An acid is a substance that donates a proton in a chemical reaction.

Brønsted Thomas Martin Lowry definition of Acid

 

An acid is a substance that accept an electron pair in a chemical reaction.

Gilbert Newton Lewis definition of Acid

 

Finally, Acids can also be also defined as substances that gives out hydronium ion (H3O+) when dissolved in water.

 

In summary, all acids will always contain the positive H+ (cation) and an anionic group in their formula. For instance, the acid HCl (Hydrogen Chloride) contains H+ as cation and Cl- as its anion.

Please read the explanations of the above definitions of acid here