Alfred Ajibola
- Thu, 18th April, 2019 @ 11:26 AM
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
John Dalton, an English chemist is considered the father of modern chemistry because of the understanding he brought into the composition of matter and the basis for their chemical reactions.
Recall that chemistry is the study of matter and the changes they undergo.
Some of the atomic theory which he postulated in 1808 had to be modified based on the discoveries of other scientists.
In this article, we will look into these atomic theories of Dalton and their modifications.
Based on the discovery made by Rutherford, atoms can no longer be regarded as indivisible because they can be further divided into the followings:
Protons: They are positively charged particles in the nucleus of an atom.
Neutrons: These particles have no charge (neutral) and are found in the nucleus of an atom.
Electrons: They are negatively charged particles that revolve round the shell of atoms.
Quarks: A quark is a fast moving energy and is comprised of both the protons and neutrons in the nucleus of an atom.
Please read on elements and characteristics of elements here.
The discovery of isotopes has shown that not all atoms of the same elements are similar in every aspect.
Isotopy is a phenomenon whereby atoms of the same element have the same atomic number but different mass number. As a result, the same element can have a different mass and density.
The difference in the mass (mass number) of isotopes is a result of the varying number of neutrons in the nucleus of their atoms.
The mass number of an atom is defined as the sum of protons and neutrons in the nucleus of the atom.
Based on the above explanations, isotopes have the same number of protons (atomic number) but different number of neutrons.
The mass spectrometry experiment conducted on (isotopic) atoms had given a confirmation to the existence of isotopes.
Some elements exhibiting isotopy include:
You can read on molecular mass and relative molecular mass here.
Also, the discoveries of isobars have shown that the atoms of different elements are not completely different.
Isobar is a phenomenon whereby atoms have different atomic numbers but the same mass number. For instance:
With regards to ordinary chemical reaction, this statement remains valid.
After the discovery of radioactivity, the various radioactive elements have shown that atoms can be created (through a process called nuclear fusion) and destroyed (through a process called nuclear fission).
Example of radioactive elements are Thorium-232 and Uranium-238
This statement is true for simple inorganic chemical reaction. With regards to complex organic compounds or molecules, the statement becomes false because they don’t combine in simple whole numbers; rather, they do so in complex numbers. For instance, glucose molecule has a chemical formula of C12H22O11.
Starch is another organic compound that contains many repeating units of simple sugars and with a chemical formula of (C6H10O5)n, where "n" is a large whole number.
Please read on sugars and carbohydrates here.
This theory cannot explain allotropy.
Allotropy is phenomenon whereby atoms of the same element exist in different forms but in the same physical state.
For instance, carbon in its solid state can exist in four different forms. These are:
Diamond
Graphite
Graphene
Fullerene
Please read an introduction to organic chemistry (carbon and it's compound) here
The above forms of carbon have got different physical properties or characteristics. For instance, graphite is soft while diamond is very tough (hard).
You can read on the physical properties of metals here.
1. His theory gave a clearer explanation to the laws of chemical combination which includes:
2. Dalton created the distinctions between atoms, molecules and compounds.
You can read on physical and chemical changes here
3. His work paved way for the discovery of atomic bomb.
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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:
