Topics in ChemistryAvogadro'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
Which of the following isn't an element of the periodic table.
According to the periodic table, elements in the same group have got the same number of shells.
The periodic table of elements is also called the Mendeleev's table.
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)
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
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
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 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)
Bitumen (least volatile)
The image below shows the process of fractional distillation as seen in an industrial environment.
Seen in the image are:
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:
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
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.
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)
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).
The process of precipitation can also be applied in the purification of impure compounds.
Other techniques utilized in the separation of mixtures are:
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.
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.
Crystallization is also applied in the purification of soluble salts that contains insoluble solid impurities.
It is used to separate components of a complex mixture in solution, for instance ink.
Below are some types of chromatography:
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Amazing facts in Chemistry
The only letters that failed to appear on the periodic table are letters:
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
NOTABLE POINTS IN Chemistry
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:
They are shown in the image below:
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:
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.
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.
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.
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
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
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