Topics in Chemistry
Gas laws in chemistry Charles's law explained Calculation questions on Charles's law Examples of Charles's law in real life Boyle's law explained Calculation questions on Boyle's law Examples of Boyle's law in real life Summary on the kinetic molecular theory of gases Postulates of kinetic theory of gases 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 mixturesAcademic Questions in Chemistry
With regards to redox reactions, which of the following statement is wrong?
A. Redox reaction are examples of chemical change
B. Reduction is the gain of electron
C. Substances that donates election during chemical reaction are termed reductants
D. Oxidizing agents are always reduced in chemical reactions
E. Oxidation occurs at the cathode in electrolysis
F. Hydrogen is a reducing agent
In chemistry, physical change is associated only with the rearrangement of molecules while the internal composition of the substance remains the same.
A. True
B. False
_____ electron(s) is a term that describes the number of electron(s) in the outermost shell of an atom.
A. Outer
B. Excess
C. Valence
D. Positive
E. Negative
F. Last
_____ is the negative electrode in electrolysis.
A. Anode
B. Anion
C. Cathode
D. Cation
E. Ion
F. Electrolyte
The above diagram shows the _____ type of bond.
A. Covalent
B. Polar covalent
C. Coordinate covalent
D. Metallic
E. Van dear walls
F. Ionic
Metals are referred to as _____ in their impure state.
A. Diluted
B. Consecrated
C. Coloured
D. Ores
E. Stained
F. Strained
Metals generally have the quality to shine, glow, sparkle, glitter, reflect light and be polished. This characteristic of metals is termed _____.
A. State
B. Ductility
C. Luster
D. Malleability
E. Hardness
F. Inflorescence
The _____ spectrometry experiment conducted on isotopic elements gave a confirmation for the existence of isotopes.
A. Mole
B. Volume
C. Weight
D. Number of moles
E. Mass
F. Amount of substance
Recall that a mixture is made up of two or more substances physically combined.
Please read the concept of elements, compounds and mixtures here.
In this article we will continue from where we stopped. In case you missed part one of this topic (which contains the concept of a mixture and various separation techniques), please read it here.
Below are other methods utilized in the separation of mixtures:
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.
It is noteworthy to state that blood is a mixture and its components can be separated via centrifugation.
Blood is considered a mixture because it is composed of a liquid called plasma and solids (called cells).
Below is an image of separated blood components via the process of centrifugation.
Using the above diagram as a reference, the following points are noteworthy:
The test tubes containing the blood are inserted into the centrifuge.
The centrifuge begins to spin or rotate when it is switched on. This is allowed to continue for 5 to 10 minutes.
On bringing out the test tubes from the centrifuge, two different layers will be observed. These are:
The sedimented lower layer composed of solid cells.
The layer containing the plasma will be seen above the sedimented solid cells.
Next, the plasma can 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:
Matter exists in 4 states. These are:
On heating a solid, it changes into liquid. If we continue heating, the liquid will eventually change into 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 is defined as a process whereby a heated solid changes directly to gas without passing through the liquid phase.
A substance that changes directly from solid to gas or from gas to solid is termed a sublimate. Sublimates always sublime on heating.
The diagram below shows sublimation in a solid that sublimes, and that's ammonium chloride (NH4Cl):
Examples of solids that sublime are:
Sublimation is used to separate two salts (or solids) whereby one sublimes and the other does not. As 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.
Distillation is a technique used to separate two or more miscible liquid that have different boiling points.
Importantly, the boiling points of both liquids are usually not at a close range.
However, understand that the term 'miscible liquids' refers to two or more liquids that can dissolve in each other (or one another).
The mixture of water and ethanol 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:
Steps involved in Distillation
The distillate is 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 less volatile.
Distillation can also be used to:
Please read on the separation of mixtures - part 3 here.
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Amazing facts in Chemistry
Plastic and Glass can decompose, but not in our lifetimes. It takes an average time of 450 years for plastics to decompose. As for the decomposition of glasses, it takes about 4,000 years
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
Below are the physical properties of metals:
They exist in solid state.
The have high densities.
They are good conductors of heat and electricity.
The have the ability to be polished, to glow, sparkle and reflect light.
They can be bent, flattened and made into sheets called foils.
They can be drawn into wires.
Iron undergoes magnetism while most metals are poorly magnetized.
They typical have high melting point.
They generally have high boiling point.
With the exception of lithium, sodium and potassium, most metals are generally hard.
They have the ability to make sound when in contact with other objects or metals.
Please read details on the physical properties of metals here
John Dalton is an English chemist who brought clarity into the composition of matter and the basis for their chemical reactions.
Below are Dalton's Atomic Theory:
All matter consists of tiny indivisible particles called atoms.
Atoms of the same element are identical to each other in every aspect because they have the same shape and mass, while atoms of different elements are different in all respect.
Atoms are indestructible and can neither be created nor destroyed.
Atoms of different elements can combine with each other in simple whole number ratios to form compounds.
Atoms of the same element share similar physical and chemical properties. They can also combine in more than one ratio to form two or more compounds.
Meanwhile, understand that the above theories of John Dalton had been modified.
Please read on Dalton's atomic theory and its modifications here
The periodic table, also called periodic table of elements or Mendeleev's table, is a table that shows an organized arrangement of the 118 chemical elements according to their atomic number.
Out of the 118 elements; elements 1 - 94 are present in nature while elements 95 - 118 are synthesized artificially.
The manner at which elements are arranged on this table reveals some similarities in their electronic configurations and chemical properties.
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)
Step 1: Identify the given parameter from the question.
Fe = 69.94%, O = 30.06%.
Empirical formula = Fe?O?
Step 2: Convert the percentages to gram. (just attribute grams to the %).
Step 3: To get the mole ratio of each element, convert the gram to moles using the formula (mole = mass/molarmass). Please merorize this formula because we always work with moles in emperical formula.
Mole of Fe: 69.94/55.85 = 1.252mol
Mole of O: 30.06/16 = 1.879mol
Step 4: Divide both sides by the smallest mole ratio.
Iron has the smallest mole ratio in our case, therefore: 1.252/1.252 = 1, 1.879/1.252 = 1.5
We now have the formula = Fe1O1.5
Step 5: Multiply each of the moles by the smallest whole number that will convert each into a whole number. (In our case, the number '2' is the smallest whole number that will make '1.5' and '1' whole numbers when multiplied by it.
For iron (Fe), we will have 1 x 2 = 2
For oxygen (O), we will have 1.5 x 2 = 3
Step 6: Write the empirical formula.
The empirical formula= Fe2O3
Iron(III)tetraoxosulphate(VI)
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:
Alkanes
Alkenes
Alkynes
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:
